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Community and Q&A

Fresh Air Supply for New Wood Stove

JoeNorm | Posted in General Questions on

Hello All,

This topic has been discussed here and in other places online but I’m still having a hard time deciphering people’s opinion vs. good scientific reasoning.

I have a brand new woodstove and bought the kit to supply it directly with fresh air. I am wondering if this item is a good idea or a bad idea in a new, pretty tight home.

The first article that comes up when searching is this one:
https://woodheat.org/the-outdoor-air-myth-exposed.html

With so much knowledge on this site about air movement, pressures, and pollutants in buildings I am wondering what people here think about this topic?

Is a Woodstoves likely drawing very little CFM? Do we have any data? If I have a small ERV isn’t that supplying ample oxygen to the stove? Would another hole in the envelope create more problem than it’s designed to solve? If the stove functions well without the supply air( I have already tested it and it seems to work just fine) should I just leave it alone?

This stove in particular is not a “guzzler” of air. It’s designed to burn slow and long, if that makes any difference.

Thanks for the thoughts

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Replies

  1. DickRussell | | #1

    My house is superinsulated and very tight (final test 0.8 ACH50), and I have a small woodstove on the lower level, with ducted outside air. We don't run the stove all the time; it's mainly from supper time to around 11pm, after which we let it burn out. While the air draw of a small woodstove is reasonably small, I didn't like the idea of having an open path for interior air up and out the chimney after the fire has died. While no stove is perfectly tight, the leakage of interior air up and out is acceptably small to me. I also didn't like the idea of having an outside air duct dumping cold exterior air "into the vicinity of the stove," as would have been required for one stove I had considered. I wanted a stove that had the outside air ducted directly. The idea of that duct dumping raw frigid air into the lower level for hours after the fire died was unappealing.

    In practice, getting the stove lit at the end of the day presents a real backdraft problem if either the range fan or clothes dryer is running, even with a nearby window cracked open. In such circumstances, I can feel the cold downdraft as soon as I open the stove door to get the fire ready. Once I get the stove lit and the flue heated, the updraft through the outside air duct and up the flue is sufficient to have either of the exhausting devices going, without any window cracked open. I suspect that the updraft during normal operation would be sufficient without the outside air duct, but I'm still glad I have it there. Your success without it might depend on how tight the house is and how tall the flue pipe is. Failure to draw air in adequately often is a result of insufficient height of the flue. Mine is around 25 ft total.

  2. Expert Member
    MALCOLM TAYLOR | | #2

    Joe,

    Your ERV is a balanced system, it won't supply make-up air for the stove. In a new, relatively well air-sealed house you have a few choices: Directly ducted, a passive vent nearby, or crack a window. Each of those have their own benefits and downsides. One factor that may determine which you choose are the requirements of both your local code, and those of the wood-stove you install.

  3. JoeNorm | | #3

    Thanks.

    But what are the negatives of omitting the outside air supply if the stove functions perfectly OK without?

    Wouldn't it be the same idea as a bath fan but it pulls even less air?

  4. Expert Member
    MALCOLM TAYLOR | | #4

    If it draws fine I can't think of any big downsides. I have much the same situation in my own not particularly tight house. You will just have to be vigilant that when you run other appliances that exhaust air, it still works then. The dryer, range-hood, and bathroom fan can all affect our stove in certain conditions.

  5. user-7433992 | | #5

    I opted to not pursue the direct vent approach due to the disadvantages mentioned in the woodheat.org article. It seemed that a direct vent could lead to smoke in the house or potentially fire risk in the vent under the right depressurization scenarios.

    I also found this article on the same site about a study that was done on this topic interesting:

    https://woodheat.org/outdoor-combustion-air-in-the-canadian-national-building-code.html

    1. Expert Member
      MALCOLM TAYLOR | | #6

      User...992,

      That's very interesting. In light of that I've edited my posts above. Stupid of me to doubt woodheat.org. They offer excellent advice.

  6. tallpinescabin | | #7

    Joe, can you provide any more info on which stove you purchased?

    I bought a Jotul F100. Jotul had the EPA report PDF available right on their website. I've looked at a couple other brands that have had the reports available as well....it seems it's common practice as part of the EPA test to measure the flue gas velocity and calculate the CFM moving through the stove in real burning conditions.
    In my case, it looks like 5-10 CFM is realistic for my stove. (5.3-9.8 measured in test burns)

    -Nate R

  7. GBA Editor
    Kiley Jacques | | #8

    Hi Joe,

    You should check out this article by Scott Gibson: How to Provide Makeup Air for a Wood Stove.

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