Our very old coop building has a fireplace in each of the six units. None has been used for a good many years.
They all have dampers, but these clearly do not prevent heat-loss up the chimney.
What's the best way to stop this heat loss? We would like to retain the option of using the fireplaces in the future if tenants wish to do so.
I would guess that we might stuff some insulation bats of fiber glass or rock wool in the openings. Does that make sense? If not, what does make sense?