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etienne

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Heating with wood or pellets ? and air heat pump ?
« on: January 04, 2017, 09:18:23 AM »
Hello,

It's winter time again and we have all these articles saying how terrible wood heating is, even pellets oven would be a catastrophy because of the soot and other small particles that would be sent in the air.

Well, there is a study of the GISS saying that the soot of organic carbon doesn't have an effect on climate, which is not the case for the black carbon (from petrol or coal) :
http://www.giss.nasa.gov/research/briefs/bauer_01/

I also believe that small particles are not all equal when talking of health hazard. When smoking was allowed in pubs in Luxembourg, you could enter in rooms where there really was a smoke cloud. I am pretty sure that if the room would have been filled with the same amount of small particles coming from a diesel engine, nobody would have survived such a frequent exposure.

I agree that wooden fire, like any technical process, needs to be done in good condition (dry and hard wood, efficient stove, not a low burning fire…), but I don’t believe that it is a major issue if smoke enters in the room each time that you have to open the stove to add some wood. There really is an issue regarding the stove quality because many people (like my parents and my parents in law) use very old  or broken stove.

I often have the feeling that people against wood heating are not so objective. The article that were presented to me just mix everything without giving any virtue to wood heating. Looks like there would be some hidden interests behind.

What is your feeling about it ? I ask the question because my wife wants to try one week without wooden fire to see if it changes something in our house.

I also have a comment about the air heat pumps. I always recommend to people installing such a system to have an extra pellets stove because the heat produced by the heat pump is equal to the electricity consumption of the compressor added to the heat absorbed in the air. When the air is very cold, you almost get an electrical heater. Furthermore, the pellet stove could work with batteries if needed.

Thanks for your comments, best regards,

Etienne

DrTskoul

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #1 on: January 04, 2017, 01:54:37 PM »
My feeling is that in a large scale wood burning is not sustainable. Too many people - on an industrial scale if demand becomes too great, wood pellets will be made from native wood (trees) instead of wood use byproducts (scrap) like the ones that are sent to UK from US to power big "biofuel" burning power stations.

On a smaller scale, depending the location and the source of wood, heating with wood can be more efficient and less carbon intensive.
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Tor Bejnar

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #2 on: January 04, 2017, 02:36:08 PM »
20+ years ago I lived where winters are cold and used a fairly efficient Amish-made wood cook stove to heat my home (that it did very well) (fed by wood cut from property - a disease was causing mature beech trees to split, so there was lots of 'dead' wood to harvest).  I wasn't particularly aware of breathing wood smoke, but when I moved south, my persistent cough ended.
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etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #3 on: January 04, 2017, 08:34:58 PM »
if demand becomes too great, wood pellets will be made from native wood (trees) instead of wood use byproducts (scrap) like the ones that are sent to UK from US to power big "biofuel" burning power stations.

That's a big question that I have. If forests had been harvested for wood pellets around Fort MacMurray, would it have reduce the size of the forest fires ?

Best regards,

Etienne

sidd

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #4 on: January 04, 2017, 08:50:42 PM »
I have a wood burning fireplace in the basement and have played with woodstoves and wood heat for a long time. In my experience, the key factors in reducing smoke are

1) fireplace/stove design
2) of course, dry hardwood fuel
3) careful initiation of flame

There are volumes written on 1), and in my view the key feature is the firebreak around which the updraft curls as it enters the chimney. 2) is quite obvious, and 3) is often neglected. Too often i see fires in well built stoves and fireplaces smoulder for up to an hour before burning clean, while a little thought before lighting the fire can reduce this period to minutes.

There are some very nice woodstoves available from Amish manufacturers, and I heartily recommend the ones with water jackets for those using water head in hydronic slabs or radiators. Especially since water heat can be supplemented with solar hotwater setups very easily.

There are versions available with air injection which reduce smoking, but maintenance seems problematic. The smoke problem can be addressed with better technique, always providing design of firebox and chimney is adequate.

sidd

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #5 on: January 04, 2017, 10:22:40 PM »
Coincidentally, I finished our wood stove project two days ago (pictures below of the wood stove and the stainless steel chimney). Right now I'm learning how to make it function properly/efficiently. As I can only buy the right length of wood - 25-30 cm - in large quantities, but don't have proper storage space for that, I'm working with wood briquettes (compressed saw dust and shavings).

As we have a ventilation system, we absolutely needed to have an airtight stove which gets its air from outside through a pipe (that runs through the floor, in our case). My problem at other people's homes who use wood stoves, is that the stove sucks all the oxygen out of the room. I always get headaches and need to step out several times.

If the chimney has enough pull, no smoke should leave the stove. In a little book I've read yesterday the reasons for smoke leaving the stove, are not enough air, chimney dimension too small (or narrowed too much due to creosote), strong winds changing the pressure.

Here's a video from the Austrian company where we bought our stove, explaining how it should be done:

! No longer available


In the first two winters (nov-dec-jan-feb-mar) we have spent in our new home, my estimation is that we consumed 2000-2500 kWh of electricity for heating and warm water (15%). In this case half of the house would remain very cold (7-10 °C), with the living quarters at 19-20 °C. Of course, with our air heat pump for warm water in the cold part of the house, it needed quite a lot of time every day to keep the 300 litres at 40-45 °C. Around a quarter of the electricity was produced by our solar panels, but the rest probably came from non-renewable resources, as there simply aren't that many in winter (although Austria does have a lot of hydro).

To replace this amount of electricity, my expectation is that we will need a maximum 1.5 m3 of beech wood every winter. This amounts to 750 kg, or 3150 kWh, from which 20% is subtracted due to stove inefficiency = 2500 kWh

My hope is that it will keep living quarters slightly warmer, and the cold part of the house closer to 15 °C. That should make it easier for the air heat pump.

All in all, this should be an improvement for the ecological impact of our home. Financially, it'll pay off after 20-25 years, but only because we bought a slightly more expensive stove (that can be used for cooking as well). Perhaps I can get the wood for free in the future. There's a lot of wood around here.
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in4apenny

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #6 on: January 04, 2017, 11:11:30 PM »
In my experience too many people rely on radiated heat from their stoves & we know where that heat goes first,---- straight up---then along the ceiling.

Circulating fans work a treat & are dirt cheap to run, we live in an old victorian 9" solid brick terraced house with only the 1 cheap basic log burner for heating 750sqft over 2 floors with 9' ceilings & as the old saying goes " it's not what you've got , it's how you use it".

With 2x 3.5ft ceiling fans downstairs as well as a camfro fan on the stove were sorted at ground floor , up on the landing the 4.5' fan does the business sucking warm air upstairs, all internal doors are left open .

Due to the mixed air there are no cold draughts even with windows or vents open , of course with any fire you need to be drawing fresh air ,not only for the fire but for us.

We're now in our 9th year of burning & use less wood each year , for the last 3 yrs we've only burnt kiln dried softwood offcuts from a local roof truss maker ( £50/yr ( oct-March) , all cut ready to use ).
« Last Edit: January 04, 2017, 11:46:15 PM by in4apenny »

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #7 on: January 05, 2017, 12:02:38 AM »
Hello Neven,

The values you give are very impressive. I just moved in an older house and data are difficult to get, but in the other house, I estimated my kWh use for warm water around 2500 kWh per year (gas heater). So you would only use 15% of my kWh for warm water. Of course I have a washmachine for clothes using warm water and we are 4 people + 2 long hair dogs (requires more cleaning), but it looks like technology has improved a lot. I never thought that air heat pump would have a good efficiency because of the air not being a good heat carrier, but it looks like times have changed.

Just for information, I heard that warm sanitary water should be at least at 50°C for bacteriological reason. Don't know if anybody knows more about it.

I know I'll have to improve the heating system of the house where I am now (I use about 20'000 kWh - 2000 liters heating oil per year and 4 m3 wood), but am still looking for the best solution. Here is an interesting document for people living in non passive house : https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationId=f2f2ebfd-ff37-4417-be92-a59400bb2665
My idea is to use these concepts, excepted that infra-red radiation would come from wood/pellets burning stove, and add solar thermal pannels for the sanitary water during the summer. Another option for the sanitary water would be a heat pump taking the heat of the radiators pipes, this would cool the house during the summer, and would be a good heat source during the winter. In that case, I could put PV pannels on the roof. It is not decided yet.

To go back to the problem that originated this topic, from what has been said, I believe that the air entrance in the house is the issue regarding my air quality problem. It was kept artificially open by a piece of plastic last winter, and when I cleaned it this summer, the plastic was absorbed by the vacuum cleaner. I thought this would not be a problem, but it looks like it is.

Thank you very much for your comments. More are always welcome.

Etienne

in4apenny

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #8 on: January 05, 2017, 12:11:43 AM »



I know I'll have to improve the heating system of the house where I am now (I use about 20'000 kWh - 2000 liters heating oil per year and 4 m3 wood), 

WOW, No wonder the polar icecaps are in such bad shape , that's 2000litres & 1.5m3 more than me, & i'm sweating here at 24deg c  :D

Edit: We do use electric immersion for our hot water( simple is sometimes best)  & our total yearly electric is 3000kw , that includes cooker/hob/tumble dryer/10kw shower etc but there is only the two of us.


« Last Edit: January 05, 2017, 01:27:28 AM by in4apenny »

Tor Bejnar

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #9 on: January 05, 2017, 01:51:14 AM »
Neven's 1.5 m3 = about 0.4 cords of wood.  I used about 8 cords of (mostly) beech that was stored (split) for over a year before using, but my house (a converted barn) was huge.  I put a 4" pipe in to allow outside air get to right next to my stove's air intakes.  Before I fell in love and moved, I was planning on modifying the stove's air intake control/opening to directly feed the outside air into the stove, bypassing the cold air entering the kitchen.  The stove was a Pioneer Maid.  This stock image shows the stove I had, and you can see the two air intake controls on the side - basically wood handled bolts that screw plates closer to or farther away from the short 3 inch pipes that lead to the firebox (on the left).  (Ah, memories!  I loved baking bread it it - my daughters and I would make animal-shaped "pretzels" with half a loaf's worth of dough, while two loaves rose.)
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sidd

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #10 on: January 05, 2017, 05:20:04 AM »
A very good design for makeup air that i have used is a double walled chimney, the outer annulus draws fresh air down and the inner one provides the usual chimney updraft. Such a design used to be made by a company called Preway, unfortunately out of business. An advantage is that you get preheat for incoming air.

I use one with a 6 inch inner and 8 inch outer diameter. The outer tube stands 1 foot shorter than the inner at the top (the inner protrudes, and both are sheltered by a chimney cap and fenced against birds and critters with wiremesh.

With regard to wood storage, i use 2x4 or brick laid on the ground outdoors and wood stacked on top. The 2x4 allows air curculation below the pile. On top of the woodstack, 1/8" or 1/4" painted plywood sheet (1/8 may break when you lift with snowload), or just tarp, in either case weighted down by bricks. The stack should have cross stacked towers at each end (or posts) and in between wood is stacked with ends exposed, they dry better that way.

Insulation will save you much wood. And chopping, splitting and stacking.

good luck.

sidd

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #11 on: January 05, 2017, 08:27:04 AM »
Insulation will save you much wood. And chopping, splitting and stacking.


Hello sidd,

I agree, but insulation is a budget issue. My situation is a little bit like described in this article :
http://energyalliancegroup.org/domino-effect-hinders-commercial-industrial-upgrades/ just that it is a normal home. A short abstract of the article is that you don't know what to do first, you don't have the budget to do everything, so you don't start.

If you first improve the heating, than the insulation, you have too much power at the end, but it's cheaper so it is easier to do it that way. So I wanted to reduce the general temperature and have fast heating device to use locally when needed to avoid that "over power" issue.

I guess you're right with the insulation and I should ask precisely how much it would cost. There are also helps that can be received for such investments, paid back by the saved energy, but my experience is that you never save as much as planned because you tend to increase inside temperature when it doesn't cost as much anymore.

Thank you very much,

Etienne

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #12 on: January 05, 2017, 12:33:11 PM »
Hello Neven,

The values you give are very impressive. I just moved in an older house and data are difficult to get, but in the other house, I estimated my kWh use for warm water around 2500 kWh per year (gas heater). So you would only use 15% of my kWh for warm water. Of course I have a washmachine for clothes using warm water and we are 4 people + 2 long hair dogs (requires more cleaning), but it looks like technology has improved a lot. I never thought that air heat pump would have a good efficiency because of the air not being a good heat carrier, but it looks like times have changed.


Yes, our air heat pump has a COP of 4.3 and works up to -7 °C (newer model apparently has a COP of 3.8). And mind you, our house is really well-insulated, according to passive house standards.

Just for information, I heard that warm sanitary water should be at least at 50°C for bacteriological reason. Don't know if anybody knows more about it.


Yes, if the water is stagnant, you could get ideal conditions for Legionella bacterial growth, which could cause possible lethal lung infections in old people and infants.

Our air heat pump has a program where it heats the water up to 60 °C once every month, but I usually turn it off manually, because the water is not stagnant and there are no infants and old people here (as of yet).

I know I'll have to improve the heating system of the house where I am now (I use about 20'000 kWh - 2000 liters heating oil per year and 4 m3 wood), but am still looking for the best solution. Here is an interesting document for people living in non passive house : https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationId=f2f2ebfd-ff37-4417-be92-a59400bb2665
My idea is to use these concepts, excepted that infra-red radiation would come from wood/pellets burning stove, and add solar thermal pannels for the sanitary water during the summer. Another option for the sanitary water would be a heat pump taking the heat of the radiators pipes, this would cool the house during the summer, and would be a good heat source during the winter. In that case, I could put PV pannels on the roof. It is not decided yet.


I don't know the situation in France/Luxembourg, but for us it was cheaper to go for PV and air heat pump, rather than solar thermal. The latter also requires more material and is more prone to defects in my opinion (which are easier to fix yourself, however, when compared to heat pumps and PV). Electricity is simply more versatile than hot water, of which there is way too much in summer and not enough in winter.

To go back to the problem that originated this topic, from what has been said, I believe that the air entrance in the house is the issue regarding my air quality problem. It was kept artificially open by a piece of plastic last winter, and when I cleaned it this summer, the plastic was absorbed by the vacuum cleaner. I thought this would not be a problem, but it looks like it is.


Yes, that could very well be the cause. Try it out.

As for insulation: I don't know your situation, but maybe you don't have to insulate the whole house right away. You know, start with the attic/roof which is where most of the heat escapes. Then insulate living quarters/room. But nothing beats insulation in the long run, so if you can get hold of some money to do it, you'll be off cheaper.

Any way, good luck. You're in the process of improvement, and that's what counts.
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nicibiene

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #13 on: January 05, 2017, 04:25:12 PM »
My feeling is that in a large scale wood burning is not sustainable. Too many people - on an industrial scale if demand becomes too great, wood pellets will be made from native wood (trees) instead of wood use byproducts (scrap) like the ones that are sent to UK from US to power big "biofuel" burning power stations.

I agree - if anyone would heat with wood, there wouldn´t be enough wood to live the way we do. With well heated buildings, all winter long. If it should be substainable, we could only burn the wood that is grown during the summer before-not more. And that would propably mean ONE warm room in a house-as it had been for centuries for the majority of people. We only started with central heating after fossil oil, gas and coal made this luxury affordable. 

As we planned our house I fell in love with the idea of a heatpump-to invest 1 and to get 4 is unbeatable.  ;D But unfortunately I didn´t think about the option of getting some serious trouble with electricity supply in the future. If I would build the house again, I would have a nice little oven in my kitchen to heat and cook with, or a tiled stove with a baking function, in addition to the heatpump system. Just to be more flexible and independent.

To get an oven in now is pretty difficult-as we have a ventilation system like Neven has and no easy option to get air for a fire from outside. But we think strongly how to integrate an oven-not to be totally dependent on electricity. At least we already have a chimney in our house-it was an old one and we left the chimney in. We have enough wood around here and it would be easy to get some. The wooden heating would be only to be prepared for emergency cases like a blackout.

Let me leave our datas of our current system here:

We need 5000 kWh/year for a well heated 200 m² house in a relatively cold area here in Germany, for heating and warm water for six persons. Our heatpump has a COP of  appr. 4 and it is supplied by sole, running through a ground collector in our garden. 

We invested a lot into insulation as well (with cellulose) although we didn´t reach passive house standard. The heatpump is powered completely by renewable (wind) energy, since some time we are able to choose a supplier here in Germany. In the beginning we had no option for that.

Additionally we are planning a PV with storage to get our own energy and to use it as effectively as possible.
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magnamentis

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #14 on: January 05, 2017, 04:49:06 PM »
what we need is an energy mix with a maximum of carbon free resources. the moment a critical number of consumers jump on a bandwagon it will become a problem, last but not least because of the simple fact that we are too many consumers (people on the planet)

further something i wanted to make a remark about many times before, one of the most efficient ways to save energy would be to live in places where less energy is needed to survive, which is why i moved to southern spain. no matter how comfortably warm i keep my house, i need one tenth of the energy to heat my house as compared to my former house in switzerland without special effort and then i can power my car with "local" sun energy and take cold showers due to minimum water temps that will barely see lows of 15C, most of the year being between 18 and 25C.

last but not least population density is an issue and some parts of the world with a potentially better energy footprint per person are much less populated per sqm than latitudes with 6 and more months of heating periods etc. even cars driven in cold climate use more energy to keep their drivers warm :-)

of course there is much more to it and much more to consider, just meant as a general idea to reduce carbon emissions and other energy consuming ingredients to human live.

BTW, batteries and their production is by now means environmental and/or resource friendly, just mentioning rare earths and the likes. again, locally produces sustainable energy is key while birth control would be another huge handle to get things under control but nobody obviously has a doable idea how to do that globally without limiting the freedom of some which again others would find ways to exploit.
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Laurent

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #15 on: January 05, 2017, 10:51:32 PM »
E.U. loophole counts wood energy as “carbon neutral.” It’s not.
By John Upton on Jan 1, 2017
Cross-posted from Climate Central   

As American foresters ramp up logging to meet the growing demand for wood pellets by power plants on the other side of the Atlantic Ocean, a new European wood energy proposal would allow the power plants to continue claiming their operations are green for at least 13 more years, despite releasing more heat-trapping pollution than coal.

Most of the wood fueling converted coal plants in England, Denmark, and other European countries is coming from North American forests. Each month, about 1 million tons of tree trunks and branches from southern U.S. pine plantations and natural forests is being turned into pellets and shipped to European power plants, mostly to Drax power station in the U.K.
https://grist.org/article/e-u-loophole-counts-wood-energy-as-carbon-neutral-its-not/

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #16 on: January 05, 2017, 11:35:31 PM »
Thank you very much for all your comments. Looks like I will :
- first replace the two wooden stove with models allowing an outside air intake. One of the stove could be with pellets so that heating oil would not be needed in that part of the house anymore, and the other one would be burning normal wood because it is in an area where we enjoy infra-red radiation (doesn't seem available with pellets stove) and because I want to use locally cut wood. Both stove will be compatible with future upgrade of the house. This is almost decided because I want a fast solution to reduce the heating oil dependence and because the stoves allow comfortable hot spots in the house instead of a general average temperature.
- second thing is to check the costs of improving insulation (the house has now an F insulation level). The attic will probably the place to start because there I can do it by myself and because heat goes up.
- third thing is to check the costs and impact of an heat pump for the warm water.
- fourth thing is to check the costs, income and incentive for PV panels for the roof.

Once the costs are known, we can take decisions and start the projects.

I will probably keep the heating oil system until it has reached its end of life (probably 5 more years) but hope to reduce greatly the consumption. I believe that the problem now is more how much energy I use rather than the type that is used.

Looks like I'll be busy for quite a long time.

Once again, thank you for all your comments. It really helps to find the best ideas. If you have more comments, please continue.

Etienne

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #17 on: January 05, 2017, 11:52:25 PM »
Today I had smoke coming out of my stove, coming into my living room! And it was because there was a huge, cold wind outside (-5 °C) keeping the chimney cold, sucking away the air from the inlet. Man, the flames would just go out, the stove would go completely dark (with a faint glow in the middle), and out came puffs of smoke through the door and the cooking lid. I guess, the stove isn't as airtight as I thought, at least not in these circumstances.

When I finally realized what was going on, I was banging my head on the wall, saying to my wife how I had written about just this problem yesterday, over here on the ASIF.  ;D

How's that for stupid!  Haha! :o

But it was a good test. After most of the wood was consumed, flames going out no longer was a problem. Normally, I would have to put in a second round of wood on the embers to burn the stove clean (the ceramic stones in it, to be precise), but naturally I didn't do that, because that crazy wind kept howling outside. And I was so happy that I had managed to burn the whole burning chamber clean this morning. Now it's all black!



To get an oven in now is pretty difficult-as we have a ventilation system like Neven has and no easy option to get air for a fire from outside. But we think strongly how to integrate an oven-not to be totally dependent on electricity. At least we already have a chimney in our house-it was an old one and we left the chimney in. We have enough wood around here and it would be easy to get some. The wooden heating would be only to be prepared for emergency cases like a blackout.


Nici, I don't know the dimensions of your existing chimney, but maybe you could retro-fit it with an air inlet next to the smoke outlet, like Sidd suggested a few comments up. A company like Schiedl might have some kind of solution.
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DrTskoul

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #18 on: January 06, 2017, 01:54:01 AM »
what we need is an energy mix with a maximum of carbon free resources. the moment a critical number of consumers jump on a bandwagon it will become a problem, last but not least because of the simple fact that we are too many consumers (people on the planet)

further something i wanted to make a remark about many times before, one of the most efficient ways to save energy would be to live in places where less energy is needed to survive, which is why i moved to southern spain. no matter how comfortably warm i keep my house, i need one tenth of the energy to heat my house as compared to my former house in switzerland without special effort and then i can power my car with "local" sun energy and take cold showers due to minimum water temps that will barely see lows of 15C, most of the year being between 18 and 25C.

last but not least population density is an issue and some parts of the world with a potentially better energy footprint per person are much less populated per sqm than latitudes with 6 and more months of heating periods etc. even cars driven in cold climate use more energy to keep their drivers warm :-)

of course there is much more to it and much more to consider, just meant as a general idea to reduce carbon emissions and other energy consuming ingredients to human live.

BTW, batteries and their production is by now means environmental and/or resource friendly, just mentioning rare earths and the likes. again, locally produces sustainable energy is key while birth control would be another huge handle to get things under control but nobody obviously has a doable idea how to do that globally without limiting the freedom of some which again others would find ways to exploit.

Save for desertification and multi year droughts....
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sidd

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #19 on: January 06, 2017, 05:22:21 AM »
"Today I had smoke coming out of my stove, coming into my living room! And it was because there was a huge, cold wind outside (-5 °C) keeping the chimney cold, sucking away the air from the inlet. Man, the flames would just go out, the stove would go completely dark (with a faint glow in the middle), and out came puffs of smoke through the door and the cooking lid. I guess, the stove isn't as airtight as I thought, at least not in these circumstances."

This I do not understand at all.  I have fine fires with wind gusting upto 40knots outside at a temperature of -15C in various fireplaces and stoves, and if anything the chimney draft gets better with wind. I have never had smoke into the room unless the flue was closed. And none of the fireboxes i used was airtight ...

Where is your inlet located and how does your chimney run ? If possible may i see a diagram of your setup ?

sidd

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #20 on: January 06, 2017, 07:53:23 AM »
Hello Neven,

It could be the venturi effect on the air inlet. I believe that you are already aware of this way of ventilation for ships. It explains why fires normaly burn better when there is wind.

I found this image

but don't know how long it will stay online. On the left side, the air can't go out, but it also doesn't improve intake. On the right side, the air is pumped by the ventury effect (stronger with stronger winds). It also works with strait chimney, but is more efficient if the air outlet is parallel to the air flow.

Another issue I have with one of my stoves is the lenght of the chimney. The stove is on the first floor so there are only 5 meters between the bottom of the stove and the higher element of the chimney. User manual requires 8 meters. The result is that the fire doesn't burn well and I never use the stove. Since your stove works properly the rest of the time, I guess this is not your problem.

Hope this can help,

Etienne
« Last Edit: January 06, 2017, 08:55:57 AM by etienne »

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #21 on: January 06, 2017, 10:30:05 AM »
This I do not understand at all.  I have fine fires with wind gusting upto 40knots outside at a temperature of -15C in various fireplaces and stoves, and if anything the chimney draft gets better with wind. I have never had smoke into the room unless the flue was closed. And none of the fireboxes i used was airtight ...

Where is your inlet located and how does your chimney run ? If possible may i see a diagram of your setup ?

I don't have a diagram, but here's a cross-section of my design (see below). The inlet runs through the floor, as our house is built on concrete pillars, and so there's a 30-40 cm space between the ground and the bottom of the house. The inlet is around 75 cm long and has a diameter of 100 mm (manufacturer recommends 125 mm, but as the inlet is quite short, I figured 100 mm would be enough, also based on what I found on the Internet). The pipe going to the exterior stainless steel chimney is around 100 cm long and has a diameter of 130 mm. The chimney itself is 3.2 metres long and has a diameter of 150 mm (manufacturer recommends 3.5 metres of length, but again I figured this would be enough, and if not I can easily extend).

If this problem persists with lower winds as well, I might have to change the thing atop the chimney. Now it's just a small roof to prevent rainwater from going in, but one can also buy things that turn with the wind.

The wind is still blowing strongly right now, so I'm going to wait until the afternoon before we fire up again.
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in4apenny

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #22 on: January 06, 2017, 11:37:21 AM »
Not to do with the draw back (but maybe) i can't understand why you felt the need to get the flue outside so quickly , unless i've missed something & your burner is so efficient it only exhausts cold air.

Why not run the flue as vertical as possible through the house  & exited at the top of the roof ,making the best use of exhaust heat?

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #23 on: January 06, 2017, 12:05:46 PM »
That was my initial plan, but due to regulations I would have had to build the chimney out of fire-resistant boards (which are difficult to come by, and quite expensive), open the floor between living room and attic, as well as make a hole in the 40 cm thick roof. In the end it was cheaper and easier to make a hole in the outer wall, and pull a stainless steel chimney (see picture in an earlier comment) through the non-insulated part of the roof (overhang).

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in4apenny

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #24 on: January 06, 2017, 12:22:08 PM »
That's a shame as secondary heat makes a big difference to us.

As for the drawback i would put that down partially to length of flue but would be more tempted to insulate the external flue between  the wall  &  roof overhang first. You want to keep the flue quite warm/hot until the gases hit the top section of the flue, this will be more important on a low/idling fire that one running hard.
« Last Edit: January 06, 2017, 12:28:47 PM by in4apenny »

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #25 on: January 06, 2017, 01:10:14 PM »
The chimney is insulated with 32mm of rock wool. It's actually a 150mm pipe within a 220mm pipe.
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johnm33

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #26 on: January 06, 2017, 01:33:43 PM »
Hi Neven, my guess is that the wind was more or less perpendicular to the roof ridge, your simplest solution is to fit a rotorvent, it'll stop downdaughts but you'll have to relearn how to 'tune' the fire because when the wind blows it''ll go through wood like crazy.

charles_oil

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #27 on: January 06, 2017, 02:04:50 PM »
Can you exit lower and come vertically up the wall - ideally to clear the roof / ridge line? 
Reason for lower exit is that here (France) only max 2 x 90 degree bends are allowed. Using a Tee at the bottom would allow easy outside access for cleaning too via the lower branch.

Good luck - here temps have dropped so my woodburner needs firing up as well and indeed low wind = poor draught, even though it vents above roof level.  Luckily I have the internal stove pipe which gives about double the radiant surface. In the room above, the pipe goes through the old hearth and is then hidden inside the old flue. 

If link works - selection of different vents:
http://www.leroymerlin.fr/v3/p/produits/chauffage-plomberie/poele-a-bois-poele-a-granules-et-cheminee/conduit-raccord-et-sortie-de-cheminee-et-poele-l1308217403?resultOffset=0&resultLimit=51&resultListShape=MOSAIC&priceStyle=SALEUNIT_PRICE&*17484=17484#result-wrapper

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #28 on: January 06, 2017, 02:07:00 PM »
Is the wind coming from the side of the house on which the chimney sits or the opposite direction?
The basic issue is I think that air pressure inside the room is lower than inside the stove. With air flow over and around the house, one would expect higher air pressure on one side than on the other. You have mentioned ventilation for your house, could that mean that there are openings on the low pressure side which make the air pressure inside the house as a whole including this room lower than the opening at the top of the chimney? With low wind velocity the lower density of the warm air in the chimney will lower the air pressure inside the stove enough to draw air from the room into the stove, but the high wind speed produces such large pressure gradients around the house that this lowered pressure (relative to the air outside the top of the chimney is still too high.
I would suggest experimenting with ways to restrict air flow from the room to the low pressure side of the house, i.e. close internal doors and block internal ventilation openings (temporarily). See if opening the window in the room (which seems to be on the same wall as the chimney) reduces smoke coming out of the stove.

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #29 on: January 06, 2017, 02:52:17 PM »
Andreas, the stove is certified raumluftunabhängig, so air pressure in the room shouldn't play a role.

Hi Neven, my guess is that the wind was more or less perpendicular to the roof ridge, your simplest solution is to fit a rotorvent, it'll stop downdaughts but you'll have to relearn how to 'tune' the fire because when the wind blows it''ll go through wood like crazy.

Yes, I think it's this, combined with the inlet below the house (and the low initial temperature of the chimney). I though it would be an advantage, but maybe there's a lot of air movement when it's windy outside, sucking the air away from the inlet.

I'll have to see about performance when it's less windy. Yesterday and today was nuts with over 100 km/h gales. And I'll discuss it with the chimney sweep as well, when he comes to check the whole thing out after the weekend.

I'll let you know if there's anything interesting to report.

BTW, how do people here view logs vs briquettes? I've been heating with briquettes so far, but found some logs with the right length yesterday, so I'm trying that out too. I also have a lot of building wood that I'm adding to the mix (only the clean wood, of course, not if it contains glue or paint).
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johnm33

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #30 on: January 06, 2017, 06:10:43 PM »
"Yes, I think it's this, combined with the inlet below the house (and the low initial temperature of the chimney). I though it would be an advantage, but maybe there's a lot of air movement when it's windy outside, sucking the air away from the inlet." It was niggling away at me this afternoon that it may be as much a problem with negative pressure on the air intake, sucking smoke back down the flue. Since the fire is clearly not airtight the pressure in the room does come into play, perhaps consider some sort of simple plenum box, on the intake, a little larger than the firebox with a simple unsnaggable louvre to prevent the downdraught. You could test whether this would help by placing something solid about 30-50cm square about 2-3cm in front of the inlet, so that intake is inhibited from gusts, but otherwise not.

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #31 on: January 06, 2017, 07:40:34 PM »
Hello Neven,

From my work experience, I would say the most stupid  and easy things should be checked first. We had a diesel generator that was smoking just like your stove, and it was the outlet that was dirty, but the supplier first checked many other possibilities. Your house is probably too new for such a problem.

Is the topic about the building of your house still available ? I'd be happy to see again how is built the bottom of the house and how the air arrives to the inlet.

I don't believe that a stove can be airtight because of the temperature that doesn't allow rubber seals. Unabhängig doesn't mean airtight but independent. I bought a CO alarm in my former house because  I didn't feel safe with a fireplace inside the living area and a mecanical ventilation. This is highly recommended for any house with a mecanical ventilation because if the inlet of the ventilation wouldn't work, the outlet would reduce pressure enough to have CO comming in the house. CO is much smaller than smoke (only two atoms) and doesn't smell. The best solution would be that the CO detection system stops the ventilation and opens an air entrance, but that's much more expensive.  Since the former house has not airtight, I believe that the CO detection was not needed.

Best regards,

Etienne



Dundee

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #32 on: January 06, 2017, 09:33:26 PM »
Wood heat is very common in this area, and many people go through 10-15 tonnes of wood in a heating season - firewood is about 250 euros/tonne if purchased but all but free if you cut your own, so homes tend to have much less insulation than they should. The only reason this works at all is because the population density here is low and the supply of wood locally is high. Historically, junipers were held in check by fire. After more than 100 years of fire suppression they are taking over, so wood from thinning operations is readily available. The value of the wood stays low because juniper makes for poor lumber and shipping it as firewood to other markets is impractical for lots of reasons (including possible spread of forest pests). Electricity is about 0.10 euro/kwhr here, which is also not a large incentive for people to use it wisely

The thread caught my attention because we have for nearly ten years, since the installation of a pellet stove concurrent with a new addition, had exactly that arrangement - wood, pellets and heat pump. Our home is about 250sqm on one floor with a central heat pump/electric furnace (in the U.S., nearly all heat pumps have condensing coils installed in what is in effect a electric forced air furnace to provide heat when temps drop below the capability of the pump - which historically has not been very good at much below 0C).  There are five doorways between the two wood burning appliances - so it takes both to heat the home. This is a high desert region, we see anything from 40C to -30C and routinely have daily temperature swings of 25C. Our house has double glazed windows and a moderate amount of insulation (high, by local standards). Generally, we need to heat only when average temperatures go below 13C. From that base point (lower than typically used for climate statistics, but supported by analysis of our particular house), we see about 1,700C degree days in a season.

Up to this winter the 'wood' portion was a fireplace insert woodstove with no forced convection and no particular claims to efficiency. Over the course of a winter, we'd use about a tonne of pellets, two of firewood, and 3,200kwh of electric heat. To plan a system, it is worth it to do some calculations with the actual fuel costs and nameplate efficiencies of the equipment you'll use. In our case, by cost per kcal the cheapest heat was the heat pump when the outdoor temp was above 7C - unfortunately in our climate, this usually means no heating is needed until the heat pump efficiency is no longer attractive. The pellet stove was next, followed by the heat pump (and auxiliary resistance heat) in more typical temperatures. The older stove insert was only economical if 'free' cut firewood was burned - with purchased fuel (and a efficiency that may have been less than 50%) it could not compete with the heat pump. Using the fireplace insert intensively cut the electric load to 2,500kwhr, not using it would bump power use to 5,000.

This year we replaced the 35 year old insert with a modern insert woodstove with a catalyst element, rated at 80% efficiency (even at very low heat outputs) and particulate emissions of 2.5gm/hour.  Local law now prohibits transferring property with a wood heating appliance that is not certified to meet efficiency and emission standards, so the old insert had to go eventually. The heat pump is now idled entirely, the pellet stove is going through about 5kg per day, and I am filling the woodstove once a day with about 20kg of juniper firewood. The low last night was -25C and the high yesterday -10C and I have both stoves turned up to about 50% of their capacity. Sounds good, but I am saving money at the cost of having to cut the wood myself (juniper has excellent heat value for a softwood, but grows like a twisted weed and is notoriously painful to cut and split). It also brings significant debris (and, potentially, wood eating insects) into the house. Efficiency is a huge plus - if I had to (like many of my neighbors) cut 6-8 cords of wood each year rather than one or two, and had to deal with an equivalent increase in ashes, bark bits everywhere, and stove tending, I probably would not do it. Insulating and sealing the house and using an efficient appliance makes it work for me.

On a wider scale and outside our little niche, wood as a fuel becomes a harder problem. The supply is nothing like the potential demand. Pelletizing it (which eliminates the pest problem) comes at a cost and growing wood as a crop (as opposed to using tops/limbs/scraps) becomes a rather grim business - I've walked nowhere as eerily dead as a monoculture pine plantation - trees in starkly precise ranks, and not a bird or mammal to be seen (as there is very little growing there to support them). It is more like a cornfield than what anyone would recognize as a forest. If wood fuel has to be transported in and purchased and is not burned in a proper appliance, it quickly becomes more expensive than all but the priciest electricity.

Lots of people claim or think they have sustainability well in hand, but there is quite a challenge to making what sounds good for one home or a few people in a favorable niche to work when applied to enough people to matter globally. It is, for example, simply not possible for an increasingly urbanized world to eat off the garden patch, no matter how well it may work for the very few privileged enough to own enough arable land to manage it. Kudos to them for not wasting fertilizer and pesticides on a non-productive (but attractive) lawn and they are headed in the right direction, but gardens will never feed Mexico City. The thing that will always, always make home heating solutions work better is to start by reducing the heat load of your home - by insulation, control of airflow and moisture  in and out, and management of solar gain (and, in the society I grew up in, accept having to wear a sweater or two). This alone lets us get through 0C nights in the spring and autumn without any artificial heat, coasting on the thermal mass of the house and the solar gain during the 20-25C day (again, something much easier to do in a desert climate than in a place that is largely overcast - but these steps also allows us to avoid using the heat pump at all for cooling in the summer). Although the payback will be longer than one or two seasons, if you can afford to eat beef, you can probably afford to insulate.

A historical tidbit - before urbanization and widespread use of (petrochemically derived) manufactured fertilizers, firewood supply was a key leading indicator of the health of what we now refer to as developing populations (usually poor and, back then, agrarian). A significant tipping point was when firewood (which had to be gathered by hand, within walking distance) for cooking was no longer available and people began burning dried manure as fuel. Since the manure was no longer going back into soil, crops declined and the bottom dropped out of quality of life. Metaphorically, one wonders what a post fossil fuel global firewood economy will start to burn when the wood runs short.

Neven

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #33 on: January 06, 2017, 10:06:25 PM »
From my work experience, I would say the most stupid  and easy things should be checked first. We had a diesel generator that was smoking just like your stove, and it was the outlet that was dirty, but the supplier first checked many other possibilities. Your house is probably too new for such a problem.

Well, the main problem, was that we had exceptional weather conditions yesterday. The wind has gone down considerably, from 100-120 km/h to 40-60 km/h, and I had no problem lighting the fire or keeping it going. The flames were flickering a lot, but never a sign of all the air getting sucked out.

It was a good lesson, though, and I'll be sure to discuss it with the chimney sweep when he comes after the weekend to check the whole set-up. I'll let you know what he says.

Is the topic about the building of your house still available ? I'd be happy to see again how is built the bottom of the house and how the air arrives to the inlet.

Yes, I posted a lot of pictures of the building process, here on the ASIF. Man, was I motivated back then!  :D

This image isn't very clear, but it gives an idea of how things look between the floor and the ground (those are sewer pipes; they are not the stove inlet! It would explode):



Here are a couple of pictures showing how I made the hole in the floor:













I don't believe that a stove can be airtight because of the temperature that doesn't allow rubber seals. Unabhängig doesn't mean airtight but independent. I bought a CO alarm in my former house because  I didn't feel safe with a fireplace inside the living area and a mecanical ventilation. This is highly recommended for any house with a mecanical ventilation because if the inlet of the ventilation wouldn't work, the outlet would reduce pressure enough to have CO comming in the house. CO is much smaller than smoke (only two atoms) and doesn't smell. The best solution would be that the CO detection system stops the ventilation and opens an air entrance, but that's much more expensive.  Since the former house has not airtight, I believe that the CO detection was not needed.

You're right. I was a bit too optimistic thinking that the stove was airtight. Okay, the lid on top (for cooking) hasn't compressed the cord below it, but I was surprised to see smoke come out around the edges of the glass plate in the stove door.

My ventilation system isn't very strong, but maybe I'll buy a CO detector to be on the safe side. I already have CO2 meter, so why not? They'll be happy together.

It was niggling away at me this afternoon that it may be as much a problem with negative pressure on the air intake, sucking smoke back down the flue. Since the fire is clearly not airtight the pressure in the room does come into play, perhaps consider some sort of simple plenum box, on the intake, a little larger than the firebox with a simple unsnaggable louvre to prevent the downdraught. You could test whether this would help by placing something solid about 30-50cm square about 2-3cm in front of the inlet, so that intake is inhibited from gusts, but otherwise not.

The stove isn't airtight (when pressure is pushing smoke out), but other than that I don't think room pressure comes into play, as the ventilation system doesn't react whatsoever. It does react when I open the door, though (makes a slight noise).

Good idea about shielding the intake from gusts, I think it would help in situations such as yesterday, when winds are really strong. I should be able to get under the house if I remove some of the gravel. Now to get over that claustrophobia... (I had nightmares after I saw a guy from the building company crawl under there)
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Dundee

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #34 on: January 06, 2017, 10:42:01 PM »
Nevin, for as long as man has domesticated fire, keeping heat in the dwelling and smoke out has been a Dark Art. Doing one or the other is easy, balancing the two is much harder. Practical wisdom in the art peaked probably just before the industrial revolution - I am always amazed to see an 18th century fireplace that is only a few inches deep but draws well. For mass market products, things have gone downhill a bit.

Enclosed stoves depend on two pressure differences, between the firebox and the room itself, and between the stove flue and air inlet (normally, to an air control damper). The former need only be a negative value - if the firebox is pressured, you will have problems. The latter (draft) is usually engineered to a specific range, which may or may not be made known to the customer. In the U.S. it is specified in inches of water and is a small number, something on the order of 5-15mm. You can buy instruments to measure it, or do it with a bit of clear tubing, a good level, and water (but both will require making enough of a hole in the flue to put a pressure tap, which is not necessarily as easy as tapping the air supply line, or a good idea . . .). So, manufacturers specify a stack height, which will in typical conditions give the right draft, or pressure difference. Too much, and the stove overfires, too little, and it burns poorly and can put flue gas where it does not belong. High performing stoves may not have a lot of room between 'too much' and 'not enough', and performance does not necessarily change gracefully when you get outside the spec.

The stack height is for a basic stack - bends and horizontal runs reduce the draft and make the stack act like it is shorter. Your specification of 3.5 meters is already on the short side as woodstoves go, shorting it a bit in what is not a straight up installation is probably not helping.

If I had your situation, I'd do three things. First (if you do not already have them) get both a smoke alarm and CO alarm. These should not be right next to the stove, but I'd have them in the same room. Even a good stove can backdraft in quirky conditions, and it does not take much to kill you. Next, I'd verify the door gasket is sealing. Do this by closing a bank note (they are the right size and do not tear too easily) in the door - if it readily pulls out the door needs adjusted or the gasket replaced. You do not need to do every bit, but do check a couple of spots on each of the four sides of each gasketed opening. New gaskets will crush down in the first weeks of use, it is common to have to tweak a new stove a bit. Finally, I'd look into adding another meter of stack.

One other issue that may be unique to my house is that the central heat blower caused real problems. The central heating unit itself is in an unheated garage, and much of the ducting is in unheated attic or crawlspace. With so much of the system outside the pressure envelope of the home, it does not take much for the blower to change pressures for the worse. I can run my new woodburning unit or the heat pump, but not both at the same time. My pellet stove has a forced draft blower, and has no problems.

If you are curious (you probably are) and have the time (you probably don't) one place you might go is the forums at www.hearth.com. It is a U.S. site and appeals to a particular demographic, so nobody there believes in global warming and there is a fair amount of incorrect folklore drifting about. With common sense and a bit of grounding in the sciences however, you can sort the wheat from the chaff. Scattered among the rest, the site has lots of sound information on the care, management and troubleshooting of a woodburning appliance.

sidd

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #35 on: January 06, 2017, 11:02:09 PM »
I too think that chimney needs to be taller and that that gusts are causing pressure drops at the air inlet, causing backflow and choking the fire with its own exhaust.

Can you add a small fan inline with the inlet ?

I burn exclusively logs, no pellets, although some friends do have pelletized wood delivered.

sidd

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #36 on: January 06, 2017, 11:58:17 PM »
Hello Neven,

Thank you for the pictures and for the link to the discussion regarding the building of your house. It was nice to go once again through the discussion.

I guess you need to keep the space under the house open in order to keep it dry, so there is not much that can be done easily in that area.

Maybe, instead of increasing the size of the chimney or adding a rotorventil, you could put a specific end on the inlet of the stove, usually air intake have such a hat. I don’t know if it protects of the venturi effect but it could.


Looks like the fences that somebody recommended me to reduce wind speed in the vegetable garden.

 
The easiest might be the rotorventil on the top of the chimney, it should have the same effect than a higher chimney, is a well known technology, but I don’t know what it means regarding maintenance. This is to be discussed with a specialist.

Pictures might disapear any time because I used links from Internet.

Best regards,

Etienne
« Last Edit: January 07, 2017, 12:58:17 AM by etienne »

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #37 on: January 07, 2017, 12:57:23 AM »
Hello,

There still is something that keeps me awake in this story.

We all agree that wind on a chimney increases the drawing of a fire.

I don't believe that the wind was going faster under the house than around the chimney, so there is no reason why the inlet would suddenly have a lower pressure than the chimney.

Anyway, if inlet and chimney had a too low pressure, air should have gone from the house in the stove, not the other way. So maybe inlet, stove and chimney are wroking properly, but the problem would be the ventilation.

The ventilation is also just two pipes, one going in and one going out, just like the chimney and the stove air inlet, the difference is that there is a fan making sure that air going in and going out  is similar. If both inlet and outlet of the ventilation have a too low pressure when the wind is blowing, inlet won't get much air in, and outlet will be more efficient than normally, so the pressure would drop in the house, and the smoke would come out of the stove. If the inlet and/or outlet of the ventilation is oriented like the wind, it makes everything even worse.

It doesn't change much of the solution, the chimney needs to draw more, and maybe the ventilation should be turned off or a window should be opened when there is too much wind. Adding a fan on the inlet of the stove would make things worse because it would increase the pressure in the stove. The CO alarm is for sure a great idea.

I hope this helps. I am not a specialist, so please ask somebody else if this is possible.

Best regards,

Etienne
« Last Edit: January 07, 2017, 01:09:49 AM by etienne »

Sebastian Jones

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #38 on: January 07, 2017, 01:52:34 AM »
I agree with Dundee.
It sounds to me as if your chimney pipe is too short for when the wind is really howling (like wow -100kph!!!!). When I install chimneys, the rule of thumb is that they should be the highest thing on the roof by at least half a metre. In addition, I always remove the cap in fall to reduce soot buildup in the top section where the pipe is cool enough for the gasses to precipitate out.
I definitely would not get one of those rotating thingys. They are great for keeping voids ventilated, but they will gum up for sure if used with a wood stove.
The latest heat pumps, even the air source ones, work just fine down to minus 20, so I would say that if you can afford both a wood stove and an air source heat pump, go for it. In Europe, I would imagine that you could heat your place just with the heat pump (not so much here in north central Yukon!).
This guide is for Yukon, rather than Austria, and for rather large houses, but it does discuss the better performing brands and models and designs. http://www.energy.gov.yk.ca/pdf/air_source_heat_pumps_final_may2013_v04.pdf

sidd

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #39 on: January 07, 2017, 02:21:12 AM »
Gusting wind can definitely produce lower pressure in the crawlspace at the inlet than at the top of chimney, especially in winds heavy as described. I should mention that burning construction lumber, even well dried is not recommended since it is softwood (at least in the USA) and will lead to flammable buildup in the chimney and eventually a chimney fire. You efinitely dont want a chimney fire. In this regard, have the chimney cleaned  (and these days video inspected ... they shove  cellfone on a stick thru  the chimney ...)  regularly. I do them once a year, but it depends on how much you burn and what.

in4apenny

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #40 on: January 07, 2017, 08:08:16 AM »
The chimney is insulated with 32mm of rock wool. It's actually a 150mm pipe within a 220mm pipe.

I see , missed that on your pics.

Did the drawback happen when the stove was hot or during initial lighting stage. What was the flue temp assuming you have a flue thermometer fitted .

I should mention that burning construction lumber, even well dried is not recommended since it is softwood (at least in the USA) and will lead to flammable buildup in the chimney and eventually a chimney fire. You definitely don't want a chimney fire.

Presumably this includes the majority of briquettes as these are softwood based as well. Seeing that you're so sure about the negative features of softwood i assume you have used a lot of it & experienced the problems you mention.

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #41 on: January 07, 2017, 08:35:30 AM »
Hello,

I just checked the formula of the ventury effect :
https://en.wikipedia.org/wiki/Venturi_effect

If you compare a situation with and without wind, you get this formula:

pressure difference is the weight of the air (kg/m3) divided by 2 and multiplied by the square of the wind speed.

p1-p2 is the pressure difference
v1 is the speed of the wind when blowing (100km/h = 28 m/s)
v2 is the speed of the wind when not blowing =0
weight of the air is 1.293 kg/m3 (certainly lower in the Alps)

so the pressure difference between no wind and 100km/h wind is 506.856 Pa, or almost 4 mm of mercury.

If you know the speed of the wind at the different inlets and outlets, you can check the pressure diffference, but since the formula uses the square of the speed, you really get a big difference when speed goes up. I know that it is impossible to mesure wind speed,  but maybe it gives a feeling of what is happening.

I guess that the wind speed is about the same on the chimney and on the in- and outlets of the ventilation, but that the in- and outlets of the ventilation represent much more surface, so you get a higher pumping out effect from the ventilation than from the chimney. Wind speed under the house is probably lower, so pressure drop on the inlet of the stove would be lower, which also increases proportionnal pressure inside the stove.

Like said before, ask somebody else to confirm this. I don't have any experience in this area.

Best regards,

Etienne

Best regards,

Etienne
« Last Edit: January 07, 2017, 08:48:17 AM by etienne »

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #42 on: January 07, 2017, 09:48:50 AM »
Hello,

I have an idea. Maybe it is stupid, and the main problem is that it is not possible to try it before.

If a pipe of the same diameter than the air inlet  of the stove would be placed just near the air inlet of the stove, but connecting the bottom of the house with the living room, maybe we could get the same pressure in the living room and in the stove, so there would be no reason for the smoke to go from the stove inside the living room.

If the air comming in and out of the ventilation is the same, there should be no air flow in that pipe, excepted when somebody opens a door or a window. Maybe some kind of system could be added to the pipe so that air could only come in which is what was needed in this context. Ventilation could also be configured so that more air comes in than out, so the pipe would only open in case of trouble.

Since the pipe would be near the stove, cold air coming in would have no impact on the comfort of the living room

This is a brain storming idea, not a proposition. The issue is that more technical systems means more breakdown risk.

Bye,

Etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #43 on: January 07, 2017, 05:36:05 PM »
It's an interesting idea, Etienne, but I don't want an open pipe connecting outside and inside as this would spoil the passive house concept. I think the best idea for now is not to light a fire when there's a storm outside.  ;D


Did the drawback happen when the stove was hot or during initial lighting stage. What was the flue temp assuming you have a flue thermometer fitted .

It happened during the initial lighting stage. As I said, I think the fact that the chimney was very cold also had to do with it (not only were there strong winds and gusts, but the air temperature was around -6 °C). Once the fire got going, it would still go out occasionally (and temporarily), but without the pitch black smoke.

Today the stove worked well again, but even so, when lighting it this morning, there were a few puffs of smoke escaping the stove. But this smoke was white and the smell was soon gone. I think this was solely because the chimney was so cold. I mean, it was -11 °C outside. After a minute or two the temp started to go up, and there was no further problem.

I read about a trick where you light a ball of paper at the bottom of the chimney (I have a small door for cleaning there, see picture further up) to drive out the cold. If you then quickly go inside again and light your fire, there shouldn't be problem.

If it's really cold again tomorrow morning, I might try that.

Learning a lot this week!

I should mention that burning construction lumber, even well dried is not recommended since it is softwood (at least in the USA) and will lead to flammable buildup in the chimney and eventually a chimney fire. You definitely don't want a chimney fire.

Presumably this includes the majority of briquettes as these are softwood based as well. Seeing that you're so sure about the negative features of softwood i assume you have used a lot of it & experienced the problems you mention.

Yes, the construction wood is pine, and perhaps you're right that it's not suitable, although I combine it with the briquettes or logs. The briquettes are soft wood too, but they have a really high caloric value, as they're much drier than logs. They burn really well, perhaps a bit too good. It seems the logs I bought (not sure about the quality, and it's from Bosnia) take longer to burn, but leave unburnt bits.

I'm not sure what is the best option for me. I can both get logs (beech) locally, as well as briquettes from a carpenter not too far from here and at a really good price, and they already have the perfect size, so I don't have to break them:



Something else to discuss with the chimney sweep, I guess. And yes, the chimney sweep comes around twice a year here (as prescribed by law), so I'm not too worried about a chimney fire as of yet. But I will ask about the construction wood. I hope it's okay if I use it to complement the main wood fuel I'm using, as I have a lot of construction wood lying around that I can no longer use.

BTW, this thread has become a nice source of info for anyone interested in heating with wood. The ASIF at its best. Thanks for opening it, Etienne.
Il faut cultiver notre jardin

mati

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #44 on: January 07, 2017, 09:25:03 PM »
the trouble with most wood stoves, is that they burn at a sub-optimal temperature.  what you want is something that burns at the optimal temperature and heats a passive heat sink (like water or brick) and then
releases that heat over time.
and so it goes

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #45 on: January 07, 2017, 10:30:11 PM »
Re: Softwood for fuel

I was warned very early about softwood, so hardly ever use it. I think the problems arise from high resin content, high moisture content, cold flues, and cold, smoky fires.  If one uses well dried softwood and runs the firebox+chimney flue hot, the problems are fewer.  The newer stoves with forced air injection also help.
In short, careful with the softwood, and definitely inspect the chimney as Neven does, at least twice a year.

I have cleaned out chimneys in which softwood was used without the precautions above, seen a chimney fire or two and fixed the results.

A fire in the chimney is quite distinctive. Apart from the fire and sparks coming out the top, the thing sounds like a railway train got in your chimney. If the flue is exposed you will see it glowing cherry red shortly before holes appear. CO2 extinguisher straight into the fireplace or stove might stop it quickly enough.

Re: Bernoulli effect, pressure drop

The formula given is correct (neglecting some few terms) but assumes uniform flow which is rarely the case. A gusting wind may easily create lower pressure in the crawlspace than top of flue through turbulent or vortex effects.

sidd

in4apenny

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #46 on: January 08, 2017, 07:41:34 AM »
Re: Softwood for fuel

I was warned very early about softwood, so hardly ever use it. I think the problems arise from high resin content, high moisture content, cold flues, and cold, smoky fires.
sidd

So only resin content then as the other problems can also apply to hardwood ( hardwoods are far from equal & some very poor as firewood) & all more likely to be a cause of creosote build up than resin alone.

As all woods are different , stove & flue setups are different , enviroment & needs are different  as well as experience level, my advice would be to source locally a consistent quality whether that's softwood/hardwood/briquettes/offcuts & become an expert on burning that in your stove.

having tried various hardwoods/fruitwoods & softwoods my wood of choice at the moment is kiln dried structural softwood offcuts, it burns hot & cleanish a little too fast but ok for me. The fire is set in a basic 8kw stove (multifuel with grate removed) with a 2" bed of sand/ashes ,only use the top vent & try to maintain flue temp above 130c ( below 250c ), get from lighting to temp fast ( approx 5 mins)   & dont slumber it out.

i Guess what i'm saying is it's the user which makes the difference as much as the fuel , in the past i've made bad fires from good wood & good fires from bad wood.



etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #47 on: January 08, 2017, 09:58:58 AM »
Re: Bernoulli effect, pressure drop

The formula given is correct (neglecting some few terms) but assumes uniform flow which is rarely the case. A gusting wind may easily create lower pressure in the crawlspace than top of flue through turbulent or vortex effects.

sidd

Yes, I fully agree, I wanted to write a response this morning to say that my calculations are just ok to get a feeling of the reallity, not to really know what happens.

Does anybody knows if lower pressure with bad weather also has anything to do with the bernoulli effect ?


If somebody has time and a blow wind tunnel available, there is a test that I would like to do just to check if my idea is correct. If somebody would know how to calculate it, it would also insterest me. The idea is :

1) to put two boxes near one another, one with just one hole (for example diameter 10 cm), and the second one with 4 holes (same diameter). The wind should blow and the idea is to check the pressure difference inside the two boxes. One box would represent the stove with the chimney, the second one would represent the house with 4 ventilation holes.

2) same test, but with a crawlspace having an inlet in the stove. Crawlspace would be simulated with a board that would be like 10 cm avay from the boxes

3) same thing, but with a crawlspace having an inlet in the house and an inlet in the stove.





There is another configuration to check, with the inlets in a third box also with a hole, instead of in the crawlspace. The third box would represent the attic or the garage.

Well, I don't believe there is any possibility to do such a test because I believe that each use of such systems have to be justified, and it probably takes a day to prepare everything and a half day use of the blow wind tunnel to perform the test.

Bye,

Etienne
« Last Edit: January 08, 2017, 05:18:21 PM by etienne »

etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #48 on: January 08, 2017, 11:03:09 AM »
I read about a trick where you light a ball of paper at the bottom of the chimney (I have a small door for cleaning there, see picture further up) to drive out the cold. If you then quickly go inside again and light your fire, there shouldn't be problem.

Well, I wonder if the same thing in the stove wouldn't have the same effect. I don't see what would be the difference between the stove and the bottom of the chimney.

BTW, this thread has become a nice source of info for anyone interested in heating with wood. The ASIF at its best. Thanks for opening it, Etienne.

Well, I am very thankfull because it really helps me. I opened the trend because I have real questions about the way I should upgrade my house. The problem you had also worries me because I would like to install similar technics.

Etienne

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Re: Heating with wood or pellets ? and air heat pump ?
« Reply #49 on: January 09, 2017, 04:12:04 PM »
One thing I'd like to add to this discussion is that a home stove of this kind is a responsibility to be taken seriously with regards not so much to the obvious fire risk as the smoke it produces (even a small amount that seems innocuous to the average person can be immediately hazardous for an asthmatic person). Get a stove with a good record for safety and a good clean air rating, and learn how to run and maintain it well.

Also, if you get this right first time, it may also save you from having to look into removal and replacement in the event of local air regulations being tightened.