Wood-Burning Stove in Passive House
Hey Fellow Tradespeople!
I’m on the hunt for a wood burning appliance for a high performance home my company is currently building, and I’m looking for advice. I have read dozens of blogs about wood stoves on GBA over the years and feel well versed in the debate and challenges of burning wood inside a home with Passive House levels of air tightness. My company also has direct experience with incorporating wood stoves in two of our high performance new construction projects; both of which struggled to perform consistently without issue, despite providing direct ducted combustion air to the units, and using balanced ventilation ( HRV’s), on both builds.
The project we’ve just dried-in is an all electric grid tied home with primary heat provided by air source heat pumps,(either ductless or a ducted/ductless combination). I have proposed electric resistance heaters as back up heat, but it may be that a wood burning appliance provides the back up heat.
I’m grateful for any advice on specific units that you all have used on your projects, as well as any strategies you recommend, ( or don’t recommend). This is a can of worms for sure, and I’d prefer to see the stove go away on this project, but doing my due diligence just the same. Thanks!
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Do you have an estimate of the heat load? You might have your range of options limited considerably by the need to avoid overheating with an oversized stove.
Electric backup heat and wood backup heat serve somewhat different functions, and one might even want to have both. Electric serves the contingency of a heat pump breaking down, and also fills in if the temperature dips below the "balance point". It can do both even when the residents are away. Wood serves those same functions, but only when the residents are present, and can also provide backup in a power failure.
Good thoughts Charlie! I'm guessing our heat load to be in the 25k BTU/hr range. Won't know until energy modeling is complete. Might be hard to find a suitable stove in that output range. Thanks for your input! Much appreciated.
I am in the process of looking for a suitable wood stove for the air tight house I will be building and here some of the model I found and liked.
A local (Ottawa, Ontario) architect who built a non certified Passive house in 2017 installed the Stûv 30 wood stove in their 1900 sq. ft. home. I am not sure how well it has performed for them over the years.
Pacific Energy - Neo 1.2 (BTU 30k)
True North - TN10 (BTU 30k)
Hearthstone - Craftsbury (BTU 40k)
Vermont Castings - Aspen C3 (BTU 35k)
Jotul - F100 (BTU 35k)
Stûv - 30 (BTU 31k)
As you are probably aware, the most common challenge for using a wood stove in a tight home is providing adequate combustion air. For more on this topic, see: All About Wood Stoves (especially the section “Can you put a wood stove in a Passivhaus?”). Also, you should tune into the BS* + Beer show on January 21. We will be talking to experts John Siegenthaler, P.E, and Albie Barden about heating with wood stoves. No doubt their use in Passive Houses will come up.
Thanks for the heads up, Kiley! I've been meaning to tune into BS and B for while now.
My favorite strategy for high performance homes is to have a 3-season room with a wood stove. If you need auxiliary heat in the house, just get the stove hot and open the door into the house. Otherwise it will perform like a wood stove in a leaky house, which in this case is a good thing.
Interesting strategy! I like it. We've tried the "fireplace on Youtube" approach, around the holidays, in our all electric home. It's not really the same thing....: )
Haha ;-) Unfortunately none of the electric fireplace options are very convincing.
Not at all! Thanks Micheal
Watching a fire is really just watching energy flows. I recommend getting a home energy monitoring system with real-time updates and a web interface. Or you can watch the "duck curve" play out on the California ISO web site: http://www.caiso.com/TodaysOutlook/Pages/default.aspx
@Charlie - Ha! Literal lol, or at least a snort.
I'll see what my Sense Home Energy Monitor has to say about this. : )
Curious what direction you took on your wood stove selection. I'm in the same boat and finding it difficult to find something tried and true.
I like the idea of locating the unit in a 3 season room but also heard of a Belgian high performance House that used a Bodart & Gonay of Belgium built in wood stove, and captured the heat off the ducts to help the heat pump hot water heater. Not sure how successful it actually is but might be worth a look https://wittus.com/phenix/
Another option is a direct vented gas fireplace. It will give you a real fire, while preserving your air barrier.
I recommend selecting a fireplace with a good turndown ratio, so that you can reduce the heat output and avoid overheating your house. We are using a 36 in Heat n Glo Slimline in a 900 ft2 great room in Zone 4. With 32F outdoor temperatures, and the fireplace set on level 2 of 5, the interior temperature rises by about 2F per hour (and this is with no support from the HVAC system).
The best part of this setup is that there are no ashes and no bark litter to sweep up. 😊 We love it!
Are you looking for a specific stove that has some mystery characteristic that works in a tight home? Or just a recommendation for a great wood stove.
I have a Blaze King and highly recommend.
Any thoughts on wood stoves with outside combustion air (ie sealed path for combustion air in, then flue out). That's what we are doing here in our "trying to tighten it up" house.
See this figure, for example:
I can't quite tell if this is two independent air paths, and so it functions something like an ERV/HRV heat exchanger, circulating inside air around the sealed fireplace, warming it and returning it to the room (while the fire burns entirely with outside air). I thought it was but looking at the figure now I'm not so sure :)
The combustion air is separate from the convection air. The outside air goes directly into the the firebox. The convection air never enter the firebox, it just circulates around the outside of the firebox and the flue. The separate convection air path is shown on page 20 of the manual.
Btw, I have been using EPA certified fireplace inserts for over 10-years, a Quadrafire in my previous house and Kozy Heat in my current net-zero, high performance house. I have no issues with combustion air, they burn extremely clean to the point that if you walk by my house you can't smell smoke, and they put out plenty of heat.
Right, thanks, yes, that makes sense. Just confused by a few extra arrows in the other diagrams :)
So these seem like a suitable solution for a passive house (or other airtight construction), no?
The one I linked (Stuv 6) is pretty small, I believe that the heat output is in the range of 16k BTU, which is almost reasonable :)