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Community and Q&A

Fireplace in tight house

Richard Marks | Posted in Energy Efficiency and Durability on

I have just starting building a new house which will have an Isokern fireplace. The hose will be relatively tight with ZIP sheathing and spray foam insulation. Besides opening a window/door to allow for the fireplace to adequately draw, what is recommended for sufficient air to feed the fire. (Please, no comments re fireplace is not practical in a tight house, etc.) Isokern sells an outside air vent but not sure if that is sufficient or the best way to go.


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  1. Expert Member
    Dana Dorsett | | #1

    Without knowing the heat rate range (BTU/hr watts, give us at least something) of the fire it's hard to say whether the outdoor air kits would be adequate or not. With no firebox door (and no flue dampers?) I'm not sure that it will be very easy to keep it from backdrafting when say, a bathroom or kitchen fan or a clothes dryer is depressurizing the house.

  2. Richard Marks | | #2

    Actually, there will be two Isokern fireplaces - one will be for gas logs and the other wood burning. Both will be large in size. No doors on either.

  3. Expert Member
    Dana Dorsett | | #3

    And the anticipated BTU rate on either of them is...?

  4. Eric Habegger | | #4

    Are you going to use both fireplaces as the main source of heat or for just occasional ambience? If they are going to be used as the main source of heat then I would get rid of the ZIP sheathing and try to make the house of just average air leakiness. There is just no point to having a tight house if those doorless fireplaces were the main source of heat. It's a total waste of money and would be very foolish in that situation.

    I know that isn't an answer you want to hear. However it creates a short circuit in many of us when we are asked for advice and have that prefaced with "Please turn off your brain while doing it because otherwise your answer might annoy me."

  5. Clara Kim | | #5

    Hey! I asked this question a year and a half ago without a lot of really productive advice. But here's the blog post about it, that links to the Q&A:

    We still have the Rumford specced in our design and we're still intending to build it (We haven't built the house yet because of other issues). I know it irritated the Energy Consultant (Mike Duclos at DEAP). We are having an external intake, and the Rumford comes with glass doors to seal it, so that's slightly better than nothing.

    Good luck and I'd love to hear how it goes.

  6. Steve Knapp CZ 3A Georgia | | #6

    What are the dimensions on your house, and where do you live?

  7. Expert Member
    Malcolm Taylor | | #7

    How has he asked you to "turn off your brain"? He has asked a very specific question about the necessity for make-up air in a tight house as he is installing a fireplace. Not every question has to be vetted by your moral compass to be deemed legitimate.

  8. Jonathan Lawrence CZ 4A New Jersey | | #8


    I looked at Isokern a few years ago when I was shopping for an outdoor fireplace. I ended going with Firerock, but the designs are very similar. The unit I have burns amazing fires. They both claim to have advanced designs that result in great fires and maybe that is true. Could be the oversized chimney or the way the throat is designed, but in any case, I would expect you would be happy with the fire output of the Isokern assuming it has the proper amount of air to feed it. And in a tight house, I am not sure you will be able to get the air you need without an outside air kit. The problem with that is it is another penetration in what is an otherwise well built envelope. If you are not planning on using the fireplace for more than a few times a year, then maybe you skip the outside air and just crack a window as needed. If you plan on using this a lot then I would suggest you consider the following:

    1) While Isokern says their units can achieve 80% efficiency with the use of catalytic combustion, what happens when the fire goes out during the middle of the night? Then it becomes a cold draft in your house.
    2) Given the diameter of the chimney (14") that could be a very large draft, and even worse if you really do need an outside air kit to get the proper combustion.
    3) In very tight/well-insulated homes, any fireplace need to be sized correctly otherwise you could end of being too hot. I made that mistake myself with one of my fireplaces.
    4) If the fireplace is to be located in a room with a cathedral ceiling then draft, combustion air and negative pressure all are a little more difficult to address.
    5) Without a glass front, soot, smell, floor burns all become bigger issues.

    If it has to be a traditional looking, wood burning Rumford then so be it. However, I have switched to closed system with doors that seal between loading, rheostat controlled blower, outside air kit, and I could not be happier. I get all of the benefits without any of the downsides.

  9. Richard Marks | | #9

    The fireplaces are more for looks that heating but want them to work well. We certainly love a good fire once weekly if cold enough. Living in Alabama not much need for lots of heating. I have no idea on BTUs for the gas fireplace and the wood burner will burn 3-4 logs at a time.

  10. Edward Cambridge | | #10

    Have you looked at the STUV 21-85 Fireplace? We're installing one in Cambridge in an old renovated victorian. I believe it is passive house rated and has an entire sealed glass front that slides up and away.
    It provides the visual appeal of a traditional fireplace but with outside air and .....'tight'.

    Not cheap though

  11. Expert Member
    Malcolm Taylor | | #11

    Those STUVs look like nice fireplaces. I hope you come back and post your impressions of it when you have had a chance to use it.

  12. Eric Habegger | | #12

    Reply to Malcolm,
    If he had said "I know this does not make sense but I have to satisfy my aesthetics" then I would have had respect for that and would have said nothing. Believe me, I learned that from my first interchange with Ms Kim. But instead he said "Please, no comments re fireplace is not practical in a tight house".

    That shut down every knowledgeable person's first thought while simultaneously refusing to admit that it was illogical. Any later admission in comments does not affect that first reaction of mine to that first comment. Mine was a legitimate and honest reaction. I'm always a sucker for ANY kind of humility in others.

  13. GBA Editor
    Martin Holladay | | #13

    Isokern fireplace components are made in Denmark. I imagine that the company is reputable and familiar with tight houses. You should contact the U.S. distributor or the technical help line in Denmark with technical questions.

    If this fireplace really has a 14-inch-diameter flue, and no glass doors, my first question to Isokern would be, "Please describe the damper. How tight is it?"

    If Isokern offers an outdoor air kit, it would seem to me that you should order it and install it. Why else would they offer it if not for tight houses?

    If you have a range hood with an exhaust fan in your kitchen, be aware that your range hood fan can introduce fireplace smells or ashes into your living room unless you provide a makeup air kit for your range hood fan.

  14. Joe Mah | | #14

    I have done some research into this. You didn't mention whether you wanted gas or wood burning. There are several gas fireplaces suitable for tight homes. However, traditional wood burning fireplaces are harder to find, and I particularly didn't like the heavy pivot door that come with them. I found a wood burning fireplaces that is suitable for tight homes but can have the wood burning openly exposed to the room.

    This is one of the few wood-burning fireplaces I've found that would work in a very tight house. They even advertise it as "keeping your home airtight" and says it can be used in Passive Homes and energy efficient homes. Much like the STUV fireplace, it has a gasketed glass door that slides down, sealing it completely, and has a fresh air intake to prevent back drafting. It has a more traditional look and more expensive however.

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