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Sealing Off an Unfinished Fireplace

  • Transcript

    LESLIE: Now we’ve got Aaron in South Dakota on the line.  Aaron, what can we help you with today?

    AARON: My question is concerning – it’s my fireplace chimney. I have a 35-year-old home. It’s a story-and-a-half and it has two fireplaces. The fireplace on the main level is in – we use it. Below it, in the basement, there is a cutout in the foundation for a second fireplace but it was never put in. So it’s just the foundation concrete.

    My question is – because it was never put in – the fireplace in the basement – the chimney was never used and it is dumping cold air into the basement. And I want to know, how do I permanently seal that off so that I’m just not taking in air from outside?

    TOM: OK. Interesting question.  Now, because it’s a second fireplace in the basement, do you happen to know if it has a separate, dedicated flue? Because it very well may have its own interior flue. Even though it’s one chimney structure, there could be two flues going up through the middle of it. Do you know if that’s the case?

    AARON: I’m not entirely certain.

    TOM: OK. Well, I would identify that. You could probably go on top of the chimney and look straight down. You’ll see these two flues side by side.  If it’s got its own flue, I’d probably seal it off from the top. If it’s sharing a flue, then what I would do is I would seal it off from the bottom. And you can do something as simple as sealing in the front of that opening with just an insulated foam panel.

    AARON: Well, you see, that is what is there right now. If I go into the basement and I look up, somebody has put a foam panel to seal it up. But it’s not sealed very well and air is getting in. And on the outside, the chimney stack is a double stack and I have cut into the knee wall, into my attic space, to look and it’s a wide-open void up there.

    So, the air is getting in. So, whether it already has a flue in there or not, I’m not certain. But I just didn’t know if there’s anything I need to do more than just putting a thermal break on every level.

    TOM: Well, you say it’s a wide-open stack. What do you mean by that when you say it’s a wide-open stack, Aaron?

    AARON: If you look at the side of my house, there is a massive chimney.

    TOM: Right. OK.

    AARON: It’s probably 4 feet wide by 2 feet wide.

    TOM: OK.

    AARON: And when I look in my attic space, I can see that it is wide open but there is nothing inside of it.

    TOM: So it’s sort of framed wide open but there’s no flue liner inside of it?

    AARON: It springs wide open like it was intended, at some point, somebody is going to put a fireplace there but no one ever did.

    TOM: Hmm. Yeah.

    AARON: So, now, it’s just – from outside, down to my basement, it’s air coming in.

    TOM: Yeah.

    AARON: And I don’t intend to put a second fireplace in and I want to finish that area.

    TOM: The goal here is to seal off and insulate anything that you’re not using without impacting the side of the fireplace that you are using. And so to do that, you need to know exactly how many flues you have and what appliances in your house that’s serving, whether it’s a furnace or a fireplace. Those need to be left alone. And the others you can insulate or seal off. And so, this may be something that has to be done by an experienced professional, because you want to get it right. But that’s the goal.

    If you’re not using it, you can seal it off. And I would seal it from the top, if I could, because that’s where the air is coming in.

    AARON: OK. Sounds good. Thank you.

    TOM: Good luck with that project, Aaron. Thanks so much for calling us at 888-MONEY-PIT.

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