Gas fireplace or other hot exhaust metal chimney/flue vent penetrations are a source of air leakage into attics. It is important to use only fireproof sealing materials at locations near or in contact with the chimney.

Fire-resistant silicone sealant is required where high temperatures are present. Do not place insulation or other building materials in contact with the metal chimney unless they are approved for that purpose. Do not alter the configuration of the metal chimney or other related components without talking to a professional heating, ventilation and air-conditioning (HVAC) contractor.

This air sealing procedure is for metal exhaust vents that extend through the ceiling into the attic space. Side-vented appliances are not addressed in this guide.