Can I Caulk Leaks in a Furnace?

Identification

• Furnace flue pipes are constructed from galvanized metal and are often placed inside attics. Sealing air leaks in and around these pipes is key to maintaining the proper temperature inside your attic. When large amounts of hot air circulate throughout the attic, it is more difficult for your home to maintain the proper temperature. Furnace flue pipes often leak around the base of the pipe through gaps left open at the time of construction.

Types of Caulk

• You can seal leaks around your furnace with caulk. Since furnace pipes get very hot, the Environmental Protection Agency recommends using a high-temperature or heat-resistant silicone caulk. Seal all visible leaks in pipes and gaps around the furnace pipes for best results. Avoid using spray foam to seal leaks around furnace pipes, as it is not heat resistant and increases the risk of fire.

After Sealing

• Once you have sealed the leaks in your furnace pipes with heat-resistant caulk, cut a piece of aluminum flashing to fit around the flue. Secure the flashing with caulk or staple it directly to the drywall inside your attic. Push the insulation back into place around the pipes carefully.

Considerations

• Hot furnace pipes must not make contact with insulation to prevent fire damage. The Environmental Protection Agency recommends placing an aluminum coil around your pipes to keep insulation from touching the pipe. Cut enough aluminum coil to wrap around your pipe plus 5 to 6 inches. Staple the bottom of the coil to the drywall and push insulation back into place up against the aluminum coil.