I have a chimney with three flues (exterior chimney on a one story house). One is for a wood burning fireplace we do use. The other two were for the furnace and water heater but are both no longer in use (no metal liners, just clay). I sealed them at the bottom in the basement (fire-rated spray foam and then plywood over the round hole). Assuming the tops should be dealt with, should I break up the clay liner to just below the concrete cap and then redo the concrete cap to cover over the holes (looking like they were never there)? If that is the case, how could I 'fill' the holes a few inches down so that the concrete filling them a few inches down inside doesn't fall all the way to the bottom?
Unused Chimney Flues
chimney
Related Solutions
You can easily do this. Take out the bricks to just below roof rafters.
DON'T take out the whole chimney because old homes often use chimney for structural support!
I did the same thing on my 1900 house - took brick out so they were 5-10" below rafters, and framed over the hole. If you worry about snow load, you can reinforce the rafters that are near the chimney.
If you want to fre up some space in the attic, you can take the rest of the bricks out just so they are a few inches below attic floor. But once again, the attic josts are most likely tied into chimney so if you go too far down, the floors will sink.
Good luck!
Sounds like you need a chimney cap
These come in a variety of sizes and shapes. They keep out most rain and snow and, most importantly, animals.
You should attach any cap with stainless screws and lead anchors. Sealant is not a big issue, since there is no need for air or water tight joints. While sealant might hold in most conditions, strong winds could rip the cap off if it is not mechanically attached.
Related Topic
- Should I plug unused chimney ports in basement
- Water – Chimney repair for old unused flue
- How to seal a unused thimble in exhaust chimney
- Chimney flue repair before installing liner for wood burning insert
- Wood – How tight a fit for a chimney liner
- Issue with chimney and wood burning insert
- Wiring in false chimney breast
Best Answer
Allow for the possibility that you or the next owner might want to use them again, and try closing them off "less destructively" - metal flashing as @bib suggests, or my personal favorite for this job, a glazed ceramic tile mortared onto the top of the flue. Stays put, sheds water, can be knocked free in the future if there's ever a need for it.