(without climbing on the roof)
Cast-iron chimney dampers are notoriously leaky by design. There are holes for running cables to the top of the chimney and they don’t close very tightly. In combination with under-pressure in the house (caused by the “stack effect“), the chimney will draw cold air down the flue – you have a down-draft problem. The results are unnecessary heat loss and elevated heating costs. The space in front of the fireplace can become uncomfortably cold, even if you have glass doors in front of the fireplace.
I spoke to the guys who sweep my chimney about this, but they didn’t really know a solution. My online research did not reveal any secret fixes, either. The common recommendation is to install a chimney top damper. I have an exterior chimney and the air space inside the flue is outside of the building envelope. We get plenty of snow and ice here in New England, and installing something with moving parts on top of the chimney seemed like a recipe for aggravation. So I decided to improvise at the bottom.
I ordered a wood stove gasket kit with adhesive (Midwest Hearth Wood Stove Replacement Gasket Kit for Woodburning Stoves – Graphite Impregnated Fiberglass Gaskets and Adhesive (5/8″ x 1/8″ x 84″ Flat Tape) and installed it on the damper door. Here is how.