air sealing and insulating fireplaces and chimneys

Fireplaces and chimneys can be important sources of air leakage. Pay attention to the heat that can escape up the chimney, and also through joints and openings related with the chimney and the fireplace…

Fireplaces and dampers

When the fireplace is not in use, close its damper. Otherwise, you will lose warm air from the rooms.

Air Sealing Chimney Make sure that the damper is tight. To test it close the flue, use a flashlight, light a small piece of paper and investigate the smoke's path. If it goes up the flue, that means an air leak. In that case seal around the damper assembly.

You may use refractory cement (don’t seal the damper closed). See if the damper is warped, and have a new one if this is the case. Damper should fit tightly: if it doesn’t, fix it. That's an important source of energy loss.

If you don't use your fireplace, seal it. If you only use it occasionally, make an airtight plug across the fireplace opening, or in the chimney (rigid board insulation backed by plywood, conveniently sealed at the edges, are a cheap and good solution).

Glass doors and other improvements to fireplaces

Even with their damper closed, traditional fireplaces are energy-inefficient systems, causing a great deal of heat to escape up the chimney. Glass doors for fireplaces and other improvements are in fact rather minor improvements. Installing tight-fitting glass doors may help, but not much.

Really good upgrades to old masonry fireplaces include modern fireplace inserts,modern gas stoves, pellet stoves or modern certified wood stoves…. By controlling the airflow through these upgrades you will improve energy efficiency and reduce you energy bills.

See for more details: Fireplaces upgrading

Fireplace Caulking: use a flexible caulk

Check for air leaks around the fireplace, namely where the chimney meets the wall. Remove the trim to inspect and to caulk, if possible or necessary. See if the joint is properly sealed. Caulk it using a proper flexible and non-flammable caulk.

Openings and cracks around the chimney

Joints, openings and cracks around the chimney should be sealed to avoid air leaks. Use a high-temperature caulk to seal them. Do not use flammable materials.

It’s common the existence of a large gap where masonry chimneys rise through the attic. If this is your case, seal the gap tightly, using a non-flammable material. Also use pieces of sheet metal to fit around the chimney, without forgetting to seal the joints with a flexible high-temperature caulk.

If you have a factory-built metal chimney do not install insulating materials too close to it, to avoid fire hazards. Keep them at a distance of at least 2’’/50 mm, install a fire-resistant material around the chimney (a metal enclosure, for instance) and use a high-temperature caulk to avoid air leaks.