Space Between Fireplace and Wall

tultexMarch 3, 2009

There is some space between the back of my fireplace and the interior wall. The gaps (on each side)are covered with moulding, but I can feel air coming into the house through these gaps and would like to seal them. Do I need to use mortar to do this, or would the canned foam insulation that you can get from places like Lowes or Home Depot be good for fixing this problem? Is there a danger that this foam will ignite from the heat generated by a fire in the fireplace? Also would a chimney balloon or chimney pillow possibly solve this problem?


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Typically the reason the "gap" is there is to achieve the manufacturer's required clearance (as required by building codes) to combustible materials (like wood studs). I'd be uncomfortable closing the gap with foam. It's hard to suggest a good non-combustible filler without seeing a picture. Mortar works if you have some kind of backing. You could also fill it with strips of Hardieboard (or cement board) and caulk the edges with a high temperature caulk. Hope this helps.

    Bookmark   March 3, 2009 at 7:48PM
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Thanks for the information! The idea of using Hardieboard and high temp caulk is an interesting one.

    Bookmark   March 4, 2009 at 12:13AM
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As ventupete wrote, the gaps are there because of building/fire code, not to mention your own safety when using the fireplace. I would be very reluctant to seal these gaps with anything. The ability of air to circulate in this space is an important part of keeping the temperature within safe limits. If you seal the space up tight, your defeating the intended purpose of the required clearances.
If the air you feel is coming through your exterior wall, it may be possible to add insulation to the wall from the outside. The air you feel may not, however, be coming through the wall.Check to see if your chimney is properly sealed where it penetrates ceilings; you may be feeling air from below rushing upward along the chimney space rather than through the wall.

    Bookmark   March 4, 2009 at 6:32AM
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I agree with mainegrower that you need air circulation in the gaps and wouldn't recommend that you completely fill them up. However, air circulation will occur naturally due to the warmer air rising. There is no code requirement, nor is it designed to pull air from inside the house for circulation in that gap. It's absolutely okay to isolate the gap from the interior of your house by sealing it off with non-combustible materials.

    Bookmark   March 4, 2009 at 1:47PM
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