Ray asked:

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 get some 2" thick Styrofoam and cut it to fit the opening. You
could also glue on some of the reflective aluminum insulation. This
could easily be removed if the fireplace was going to be used.


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')