Wood Burning: Resilient and Carbon Neutral

Resiliency

Thomas Homer-Dixon is a smart Canadian with some keen insight on the problems that our species face. His book The Upside of Down is an exploration of the biggest threats facing us and the planet. Two of his top five are the problems that I think will have the most influence on our way of life this century: Peak Oil and Climate Change.

One of his observations is that our support systems are much too brittle. Take food, for example. What would happen if there was a massive, North America-wide diesel shortage in February. How long would it take for Edmonton to be in big, big trouble? We have no resiliency in our food system. It relies 100% on the widespread availability of cheap diesel fuel.

The picture above is a Scan Andersen 10 wood burning stove. We are having one installed on the main floor of the Mill Creek NetZero Home. NetZero energy homes are a brilliant idea, and I hope that they spread like wildfire. However, they, like almost every aspect of our lives, depend very heavily on abundant fossil fuels. Our ventilation system, our solar hot water system, and even our solar panels depend on there being juice in the grid. So what happens if the juice runs out one day?

Having a wood burning stove in our home gives it resiliency. No matter what happens to the fossil fuel grid, we will be able to keep it warm (uh, if we have the wood, that is).

Climate Neutral

Anyone building a NetZero Energy home goes through the same process. Once you've eliminated 90% of the need for heat, where does that last 10% of heat come from? The Riverdale NetZero Project is attempting to store summer solar energy in a big hot water tank (a swimming pool, really). We've decided to just use straight coal-powered electricity to heat our house in the dead of winter. There is no perfect answer, but it's impossible to ignore the simplicity of the oldest form of human-used stored solar power:dead trees.

The wood that we'll burn in our stove will be salvaged from construction waste or trees that were going to be cut anyway. Its carbon will be released to the atmosphere either way, so it may as well let us displace some coal that we would have needed to use for heat anyway. So wood is a carbon-neutral heating option. It's not the greatest for ground-level pollution levels, though.

image courtesy of treehugger.com

The above image shows the difference between the ground-level pollution emitted by an EPA-Certified Woodstove (which the Scan Andersen 10 is) and a gas furnace.

We've decided that, since the Mill Creek NetZero Home will burn much less wood than depicted in the picture - about 3/4 of a cord of wood vs. 6-10 cords for a conventional house - and since our household is car-free, the pollution burden is acceptable for us to impose on the neighbourhood. We chose one of the cleanest stoves out there. The Scan Andersen 10 is rated to emit 3.13 grams of particulate matter per hour, and it's 78% efficient at converting wood to heat. Plus we'll make sure to burn only really dry wood for a cleaner burn.

The stove will be surrounded by concrete floors and in front of a brick mass wall, so the heat it projects will be absorbed and slowly released over the course of 24 - 48 hours. It will be beautiful to watch, and the heat quality will be very pleasant. I can't wait to fire it up for the first time. And I can't wait to see my first dumpster full of old dry 2x4s next summer.  We'll essentially be converting construction waste to electricity, which is a pretty great way for a tree hugger to keep warm.

(cross posted at www.raisingspaces.com)

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Conrad:
Nicely documented site. Have been following various sites for awhile and wanted to comment on the wood stove issue. I don't know if you already bought this stove. We live in Edmonton and have had a woodstove for the past 12 years, it is a DutchWest woodstove by Vermont Castings. It has a catalytic converter on it so the pollution is very small at just 1.4 grams / hour. We specifically bought this stove because of this factor. It comes in 3 sizes and though it looks more traditional than the Scan Andersen, it emits less pollution and is made in North America by a Canadian company so it is a more local supplier. The efficiency rating is the same as the Scan Andersen, which unfortunately is made in Denmark ( unfortunate for the distance it would ship ).
Also your comment about the carbon neutral footprint is one that escapes most people's attention. If the tree falls over and rots in the forest it emits the same carbon as if you burnt it in your woodstove. Something we didn't think about 12 years ago but nice to know nowadays.
I would have increased the thermal mass of the stone surround if I was doing it today, we do have our furnace ducting setup to collect the heat from the living room and distribute it around the house by running the fan so even during the recent cold snap we can maintain a comfortable level in our house without using our furnace, of course we wear slippers all the time on the hardwood floors so our level of comfort is closer to 19 degrees than 21.

Thanks Warren.

I'm afraid we're past the point of changing our minds about the stove. I agree with your comments about sourcing more locally. The North American stoves are not nearly as attractive as most of the European ones, plus they're much bigger (generally speaking), so we ended up going European.

Your setup sounds pretty nice - impressive that you weren't using your furnace, especially given the recent weather. Don't you need to service a catalytic stove more often?

Conrad:
Our particular stove comes in 3 sizes, we have the large size ( they have small, large and extra large - like pizzas I guess) and in the 12 years we've had it we replaced the catalytic component once. It is a ceramic honeycomb structure basically like an automobile's. Not cheap at a couple of hundred dollars, but what a cord of wood cost and it lasted 8 years. We have the chimney cleaned annually, as you should. The amazing feature of the stove is how easily it lights and a very complete burn so we have little ash that we spread on the garden or add to our compost. It has an ash pan which is a nice feature as well.
The look is more "old-fashioned" than the Scan Andersen but the emissions sold us on the unit. Of course the look is a personal choice so hard to say what others like.

Hi Conrad,

I was wondering about your basement. Will you be routing a vent downstairs (with a fan) from your wood stove as well?

Rosemary

Hi Rosemary,

We need to keep the suites separate, air-wise, so we won't be doing that. It's a good idea though. I'm hoping that some of the extra heat that is stored in the concrete slab will radiate downwards into the suite (by convection, heat does rise, but by radiation it travels in all directions).

Conrad

Hi All !

Do anybody come across R-2000 Building Science program?
Is it Possible to get some tips on Exam questions please?

Thanks and regards
Vara

It may be worth it to consider the effect of the stove when it is not in operation, which would be most of the time. Ventilation requirements of a wood stove, whether it be sealed combustion or open combustion (using room air) means that when in use the house must draw in cold outside combustion air to balance the expulsion of air through the flue. Either you have a hole in the wall somewhere with a little manual louver that is oh so easy to forget to close (but harder to forget to open once your fire dies down and begins backdrafting smoke into the room) or your stove's cold air intake ensures that when it is not burning, it will draw in cold air and eject it our the stack, this is called stack effect. The net result is that either the hole in your wall becomes a big heat leak (it isn't insulated or well sealed) or the cold air stack effect in your sealed combustion unit creates a very cold stove that will suck out heat as effectively as it will radiate heat when in use. In short, the ventilation requirements and techniques prevent wood burning appliances from being anything other than a net energy loser for a given building.

Automated, well sealed louvers on a sealed combustion stove would go a long way to solving this problem, but I'm not aware of any such system available on the market...

Conrad, Some of the respondents have inquired about using a masonry heater in your house. These are very beautiful heating units but might put out too much heat for your application.
In the 1980s, Jorg and Renate Graf built an imaginative passive solar house which was featured in Harrowsmith. Some of the heat came from a wood stove which was configured to maximize the heat recovery. Jorg ran the stove pipe into the wall behind the stove. He had built a serpentine chamber similar to a masonry heater to force the smoke to take a longer, slower path. The heat was absorbed by the thermal mass built into the wall structure. The wall radiated heat for many hours after the fire went out.
A similar arrangement could be a compromise between a wood stove and a masonry heater.
Jim

Mississippi John
Mississippi Mills, Ontario

Hi there:
I seem to be posting on here a lot lately... I guess this is because my wife and are are scrambling to put the final details on our building plans so we can engage a bulder to build our near netZero house inspired largely by Conrad's house, as well as other double walled systems. The idea of a woodstove is one of the many balls I'm trying to juggle right now.

We we're thinking we would bring along our Jotul 500 stove when we move (rated at 2.8 grams/hour), but I am concerned about what the visiting contributor stated on May 17th, 2010. The Jotul stove has a fresh air kit, but I'm told it is a passive item, and not coupled directly to the stove. A such, it will dump cold air into the house when there is a draw, such as when the kitchen fan is on. I have been speaking to local woodstove retailers here, and one has told me they are being told that woodstoves may be a poor choice in very tight homes such as this.

So, for all those folks out there in r2000, straw-bale, energy star or netZero tight houses, what is your experience? Do you have a fresh-air make-up? How did you do this without compromising the envelope of your house? thanks.

We searched for a stove that would allow us to run the fresh air intake directly into the combustion chamber. Wouldn't that make sense? It would allow for a closed pipe from the fresh air intake, through the combustion chamber and up the chimney.

We couldn't find one, so obviously the manufacturers of wood stoves know something that I don't, or just haven't ever worried about air-tight houses. Our wood stove allows a draft to enter the house from the chimney directly into our living room.

As far as running the kitchen fan, one time we turned it on just as I was starting a fire and the stove back drafted, with a puff of smoke entering the house. With a bit of attention, though, it never did happen again. Once the fire is burning, the kitchen fan doesn't create enough of a vacuum to affect it. We don't have to worry about the kitchen fan and the dryer being on at the same time since we don't have a dryer in the house :)

All, in all, the stove was a major net contributor to our heating last winter (we're not using it this winter so that we can measure the house's true energy consumption). Our baseboard heaters only ever turned on in the middle of the night.

Even with the stove, our house measured at 0.9 ACH @ 50 Pascals, so the impact wasn't too bad.

I would recommend getting a wood burner if you're at all interested in one. We do have a fresh air make-up that is attached to the back of the stove.

Mississippi John
Mississippi Mills, Ontario

Conrad - thanks for the feedback. FYI - the reason you wont find a newer EPA approved stove with direct coupled outside air is because they depend on super-heated air to increase the efficiency of the burn. Cold outside air would affect the way they operat. Most of these stoves draw indoor air from the back, bringing it though a sleeve in the stove, which super-heats it. This is part of the science.

I would love to see more info on your fresh air port; how it is installed, if it is an 'off the shelf' product, whether you can shut it when not using the stove, etc.

also, was your blower door test conducted with the fresh air port?

Thanks.

Hello Mississippi John,
I live down the road in Middleville. It sounds like we have similar goals and dreams.
I have a couple of suggestions for make-up air and heating info. In the 1980s, for Harrowsmith, I photographed a man named Dan Fugler, who worked as a researcher for CMHC. The story was about make-up air for furnaces. If memory serves me right, he said to run a fresh air pipe from outside, place the open end near the furnace so the combustion air would be sucked into the furnace and household air would not be compromised. It is better to run the pipe from below the stove, so the cold air does not drop into the space, increasing the chilling effect. If a damper was installed in the pipe, it could reduce the unwanted cold air. When the stove was drawing, the damper would open.
In my research into energy efficient homes, I have spoken to several people at CMHC. They are very knowledgeable and willing to answer questions. They also have a very good resource library. In a few cases, I have spoken to a man named Michel at the resource center and he has directed me to the appropriate researcher. If Dan Fugler still works for CMHC, he may be able to answer your questions. You might also find info on fresh air inlets on the CMHC website or at their library.
Recently, the Green Building Advisor (GBA) website has had a couple of blogs and discussions which could help you. About five weeks ago, there was a Q & A which began with an inquiry about a kitchen fan which vented 1200 CFM. Many of the respondents commented on providing make-up air in an airtight house.
In the past week or so, there was a GBA blog and discussion about masonry stoves in an energy efficient and airtight house. This discussion went on to talk about whether a masonry stove or wood stove were overkill in a tight passive house. There could be some info which might help you.
There are a couple of local (Eastern Ontario) people who could help you with some of your design questions. Ross Elliott is a former R2000 builder. He has also built strawbale houses. He is an trained and certified energy auditor. He is a very nice man and extremely knowledgeable about building and energy issues. His company, Homesol, is based in Almonte.
Chris Weissflog, from Kemptville, owns a company called Ecogen. He specializes in designing and installing solar hot water, PV and wind systems. Chris is a trained engineer and is very interested and committed to solar generation.
Bob Argue works for EcoPerth, in Perth. He built a passive solar house with high levels of insulation. The house includes a wood stove. He may give you some practical info based on experience.
Frank Tettemer is a builder based in Killaloe. He has built straw bale homes and other energy efficient homes. He is knowledgeable about passive solar and PV. His house has a thermosiphon hot water system connected to a solar panel and his wood stove.
I hope this info helps. If you would like to meet and exchange ideas, I am in the Lanark directory.
Good luck - Jim Merrithew

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