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How do you seal up an old fireplace chimney?

Anonymous Nov. 2, 2017, 10:06 a.m.

I have an unused fireplace that feeds a lot of cold into the house so I would like to insulate and shut it. How can I do that in way where I may be able to use it again in the future if we need it? Thank you.

Responses (3)

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Samuel Leith Sept. 6, 2018, 7:42 p.m. Reply

Instead of insulating the exterior of the brick chimney, we were actually advised to fill the interior cavity with loose fill insulation. I reckon this serves a similar purposes as the exterior insulation suggested in the previous post, but I see 2 advantages:

-exterior esthetics  remain unaffected

-there is a bedroom located on the other side of the inner wall of the brick chimney. Filling the chimney with insulation should better address the cold wall of that bedroom. 

Ecohome Sept. 10, 2018, 4:02 p.m. Reply

 

Hi Samuel,

True, not insulating the exterior keeps the aesthetic the same, however, depending on how the chimney integrates with the wall of the house, I would be concerned that the stone or brick would still act as a thermal bridge. I think what you describe would actually lead to a colder bedroom wall. If the stone or brick is entirely insulated outside it will become part of the interior conditioned space, but if any of it is left exposed from the interior through to the exterior it will continue to conduct heat. 

The main reason we propose exterior insulation would be to create an envelope around the chimney to eliminate any thermal bridging. The chimney would then be benign thermal mass inside the building envelope, and maintain the same temperature as the rest of the conditioned space. The most important part though is to stop the air flow, so again, what you mention would work, but always make sure to create a good air seal.

Thanks for you input!

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