Is it safe to close off an unused flue to a basement fireplace? Does anyone have any DIY tips for how to go about that or with the state this is in do I have to call in a pro and sell off my firstborn?
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Closing off an unused flue
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Looks in rough shape. As long as nothing is using that flue, a flat pc of stone, like flag stone, or any metal plate will do. If you really want a tight seal, pump some silicone or urethane caulk around opening perimeter before laying the stone or metal over top. If you do it sized right, you can put the cap back on over everything.
Being in the "live free or die" state, I just fashioned a tapered plug from 3" rigid insulation board and pushed it in snug, so that there were no cracks for any air flow to occur. Easy enough to remove. You might also want to put some insulation in above the fireplace damper to help prevent any warm air and moisture inside the house from rising into the chimney.
Do you think it is ok to leave the inside in the current shape if closing off? I took off the cap and reached and there and it is deteriorating really bad
I should add, it has a thin piece of slate covering it. I assume you mean you would be worried about sparks from the other flue? Even in the rare event it ignited, I don't see a problem.
Mostly I'd be concerned about it melting due to the heat from the adjacent flue. The OP's flue tiles look like they almost touch each other.
Yes, if you aren't using the bad one, and, the one being used is in good shape, I would think you would be fine. You may want to block off the damper below in the one not being used, and put something obvious there, so just in case, you don't forget, or another person decides to light a fire in the bad one.
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