I live in the Cleveland area. I have a brick fireplace that was converted to gas. I’ve been in the home (1992 build) for 5 years and I have never used it. It’s drafty, so I put mineral wool insulation in the ceiling of the firebox, covering the damper.  Some improvement, but when I recently looked inside, I discovered snow and ice on walls and floor (see pic). The ash pit was dry. I plan on cleaning and de-icing the firebox and then applying a sealant. I have to figure out how the moisture is getting in (I suspect cracked caulking). In the meantime, I plan on re-insulating the interior of the fireplace. Place 2” XPS rigid foam board in the firebox on the ceiling against the damper, the 3 walls, and on the floor, which will also cover the deteriorating lid of the ash pit. I will use closed cell spray foam to fill gaps between boards to create an air barrier. I will then fill the firebox with mineral wool insulation.  Finally, I will follow Mike Guertin’s recommendation to “clearly label the firebox as non-functioning so that someone now or in the future doesn’t try to start a fire there.”

Any recommendations for a sealant? Does this insulating strategy (air barrier) make sense?  Thank you.

What to do With an Unused Chimney

Remove it entirely, take it down to the attic floor, or cap it—what is the best option?

By Chuck Bickford | June 24, 2024

https://www.greenbuildingadvisor.com/article/what-to-do-with-an-unused-chimney