Air Sealing with an Open Hearth Fireplace.
I am renovating my 1978 Split foyer. The bottom half of the house is a finished basement that is partially above grade, the exterior on this portion is brick which I am not changing anything on.
The main level of the house is sided in masonite. I am replacing all of the masonite, filling the wall cavities with rockwool, sheathing with zip, replacing the old aluminum windows and maybe (haven’t decided yet) adding a layer of R5 foam CI. My CZ is extreme southern part of 4a.
Unfortunately, in the finished basement there is an open hearth fireplace. What is the best way to deal with this fire place? We have never used it, it was simply in the home when we bought it. I am thinking about trying to seal it with a fireplace plug and then maybe adding some insulation in the fireplace under the plug and then putting something decorative over the opening to the fireplace. I just am not sure if this is a sufficient or safe way to try to air seal the fireplace.
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There are spring loaded operable chimney caps available. A stainless steel chain is dropped down through your chimney and attached to the inside of your hearth. Releasing it opens the cap on top of your chimney for fires. Pulling down and securing it closes it up.
How good the seal actually is vis-a-vis Passive House standards I do not know, but I'm guessing mediocre. This is what I'm going to do to the chimney on my 150 year old home.
Thank you, I didn't realize that was an option. I'll look into that. Although I'm doing my best to help the air seal with this house I'm sure it will be far from passive house standards in the end. So that's not quite my goal. Just as good as I can reasonably get it.
I have read that sealing the Chimney end would not be as safe as sealing the fireplace end since it would allow moisture to build up because there is no air coming into the flue from the outside in order to dry it. Then mildew and mold could grow. Is this an unfounded concern?
Would there be any benefit or need to insulate the opening of the fireplace since I do not use it. I assume the air in there would still be relatively similar to the outdoor air even with a chimney cap? I've thought about filling it with Rockwool.
I"m no expert, but I hesitate to seal fireplaces from the bottom up. I also don't understand how moisture would gather inside a capped chimney and grow mold.
If I understand it right, the thinking is that condensation can happen on the inside since the fireplace is partial outside of the heated and cooled space and partially inside. I am not sure if this is a valid concern though.
I use the top caps for active fireplaces and they seem to work well, except when one stuck closed and the house filled with smoke...
Since the top closing flue stops rain from entering, I cannot think of any reason for excessive moisture to be in the flue.