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We are bulding a new energy-efficient house in western Canada, and are looking into an outdoor wood boiler

Our house has a hydronic heat system, Warmboard subfloors, double exterior walls, R-60 ceiling, etc... We are installing 6 vacuum-tube solar panels, a small electric boiler, but want to use an outdoor wood boiler for the majority of the heating needs during winter.

There are so many options out there and all claim to be the best, most have efficiency ratings in the high 80's. We would like to heat a 500 Gallon + tank then use closed loop systems (passive in the tank) to heat multiple buildings.

Any suggestions?



Asked by Sam Emke
Posted Jan 28, 2013 2:07 AM ET
Edited Jan 28, 2013 11:10 AM ET


8 Answers

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Outdoor wood boilers are expensive, inefficient, and highly polluting. There are also many reports that they don't last very long. Some very expensive boilers have developed leaks or otherwise failed after only a few years.

I strongly recommend that you avoid using an outdoor wood boiler.

If you want to burn wood, you might consider an indoor boiler like the Tarm. More information here: Tarm Biomass.

More information on outdoor boilers:

Outdoor Wood Boilers

GBA Encyclopedia: Boilers

New Program to Cut Outdoor Wood Boiler Emissions

Outdoor Wood Boilers

Answered by Martin Holladay
Posted Jan 28, 2013 5:35 AM ET
Edited Jan 29, 2013 8:02 PM ET.


I second Martin's advice.

Claims about efficiency do not reflect the fact that these furnaces are "idling" much of the time.
When the furncace is "idling" the wood is smoldering - not burning efficiently - which leads to creosote buildup, thick smoke and air pollution.

Several people in my area have outdoor "woodsmokers" - as I call them.
Anybody who uses one seems to go through substantially more wood than one would expect if the house were heated with an airtight stove.

Answered by Lucas Durand - 7A
Posted Jan 28, 2013 3:58 PM ET


In the litigious US people have even been taking neighbors to court over the woodsmoke air pollution from wood boilers. Until they make modulating versions rather than simply air-starving the full-fire it when the tank's aquastat is satisfied and smoking heavily for 10s of minutes the way most currently operate. Sometimes even the STATE is taking the woodboiler operators to task! See:


Canada is not immune from these actions eitherL


If you're committed to going down the outdoor wood boiler road, as with any heating system, sizing the burner to the peak and average heat loads is important for optimizing efficiency (which will minimize the sooty emissions impact.) A 75% efficiency burner that's actually burning is a far more efficient and clean burner than an oversized 88% burner that spends the majority of it's time in smolder mode. But with a high-R house almost ALL wood boilers are way-oversized, and the only way to limit the pollution is to starve them of fuel rather than air, which takes much of the convenience factor out of it.

Depending on your actual R values, thermal mass, and solar gain, you may have a surprisingly short wintertime heating season compared to conventional housing. The description of the house and location is low on detail - Western Canada is a pretty broad description that covers a huge range of winter conditions between differing locations, so it's hard to guesstimate just HOW short your heating season will be, but if you've been living in batt-insulated 2x6 construction with R30 attics and U0.5 windows you could be in for a big surprise.

In a Kelowna BC climate you might be looking at only needing to run the boiler intermittently, even in the December-February period if the house is carefully details for passive solar gain, thermal mass and low thermal bridging of the structural elements. If you're talking Whitehorse Yukon it's a different story altogether, and Nanaimo BC would be yet another story.

Solar radiant with a woodstove (not hydronic) backup can work and work well in a variety of climates, with far less air pollution, and lower up-front expense than a wood boiler.

Answered by Dana Dorsett
Posted Jan 29, 2013 6:35 PM ET


Thanks Martin, Lucas & Dana for your input.
a little more information about our house.

we are building in Tatlayoko Lake BC. that is 51, 41 N 124, 24 W. we are in the coastal mountains.

the house we are building is double walled offset studs to reduce thermal bridging, total depth 10 inches, R 38 in the walls. the Ceiling is R 60, 24" blown-in. the Windows are fiberglass, triple pane, U-value .19, SHGC .69,(centre of glass ratings). We have tried to build as energy efficient as possible.
We have a small cabin on the property as well, and plan on adding a shop & greenhouse, we thought a gasification wood boiler could heat all buildings from one central point. there are a few on the market, and was hoping to hear feedback from anyone who had one or is familiar with them. I thougth they are similiar to the Tarm, only larger (outdoor of course). we would heat a large tank of water as they burn at full heat as long as there is fuel, no dampering them down.
We are also having a wood stove ion the main floor.
200 cfm HRV, and a 1100 CFM MUA with a coil from closed loop heated water(this is for 1100 CFM range hood).
with the added information, perhaps it will stimulate other thoughts. We are at lockup stage.



Answered by Sam Emke
Posted Jan 30, 2013 1:09 AM ET


To clarify, are you considering something like the Garn wood gasification boiler?
A gasification boiler with large storage tank is a different animal altogether from the average outdoor "woodsmoker".
You do all your woodburning at one time and at very high temperatures which "charges the battery", so to speak, then you coast off the stored heat for a while.

I've always considered these units an interesting option for a large homestead with multiple heated outbuildings or perhaps for a multi-unit dwelling in a rural setting, but calculating heating loads and right-sizing a unit for such applications is out of my ken.

Some things to consider with a unit like the Garn:
They are expensive.
They are more expensive when you factor in the extra components required to plumb it to various outbuildings.
They are more expensive yet when you factor in the cost of a well insulated shack to house the unit itself (you want to minimize stand-by heat loss from the tank to the maximum extent possible).

Answered by Lucas Durand - 7A
Posted Jan 30, 2013 11:23 AM ET


See hearth.com if you'd like more info on all this wood stuff. You can put your Garn inside if you'd like and do not absolutely have to have a massive water tank (though i think it is a good idea to do so) if you choose a different brand. A guy I spoke w/ here ran a Greenwood ( I think it was) with only about 60 gallons of water that is designed as part of the machine, and says it had done fine for the two years he'd run it when I spoke to him. Either way, expect to spend at least $7K for one. BTW: 1100 cfm kitchen exhaust fan? Mercy.

Answered by John Klingel
Posted Jan 31, 2013 3:11 AM ET
Edited Jan 31, 2013 3:14 AM ET.


The power pallet GEK wood gasification electrical generator is about 10,000 for the kit or 15,000 ready to go and burns wood chips. I think it does about 10KW of power, but also maybe 80,000 BTU which they have an attachment for heating hotwater and houses (or make your own out of a boat heat exchanger). The gasification technology is one of the cleanest ways to burn wood.

Answered by Patrick Walshe
Posted Mar 6, 2013 2:22 AM ET


Every thing said so far is good and true! BUT! If you want to heat with wood and do it cleanly and efficiently, you should investigate and use a " masonry heater" ! Masonry heaters are sort of like fireplaces with additional channels for the burnt gas to pass through and store heat. They burn a relatively small amount of wood once or twice a day but burn it hot and fast and store most of the heat in hot bricks to even out the heat output. Masonry heaters burn cleaner than all but the very best of pellet stoves! They pretty much need to be designed into the house as most of the heat output is radiated from the hot masonry, so a central location and open floor plan are important (less so in a super insulated house), They are not cheap with installed costs of $10k up, about double the cost of an ordinary fireplace. Masonry heaters often include an oven and are often situated between a kitchen and "great room.

Answered by Jerry Liebler
Posted Mar 6, 2013 10:05 AM ET

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