Cementing Furnace Exhaust Ductwork and Chimneys

Protect your Home from Fire by Cementing Furnace Exhaust Pipes to the Chimney

By Mark J. Donovan




During a recent home inspection of my vacation home, the home inspector discovered something that I had missed before with my hot air and hot water furnaces.

The tin exhaust ductwork associated with each furnace was not properly seated into the chimney flue holes.

Moreover, there was no furnace cement applied to the chimney and exhaust pipes were the pipes connected to the chimney flue holes.

As a result, my home had been at risk of fire. If either exhaust furnace ductwork pipe had separated from its respective chimney flue hole, a fire could have ensued in the lower level of my home.

To resolve the problem I first pushed each exhaust ductwork pipe into its respective chimney flue liner hole at least one inch. I then applied a thick layer of furnace cement around each exhaust pipe where they connected into the chimney.

To apply the furnace cement I first used a wet sponge to clean the furnace ductwork and the surrounding chimney mortar. I then used a putty knife to apply the furnace cement to the furnace exhaust ductwork and chimney. I made sure to apply a good and thick one inch diameter bead of furnace cement around both the ductwork and chimney.

I also inspected the rest of the furnace ductwork for missing screws. Surprisingly I found a few missing screws in the furnace ductwork.

With both furnaces, the screws to the ductwork were missing where the ductwork pipe directly connected to the furnaces.

Apparently the furnace service technician removed the screws and ductwork pipes when cleaning the furnace but failed to reattach the ductwork pipes using the screws.

Again, this was another major fire threat averted. I used small self tapping screws to properly attach the furnace pipe sections together, and to attach the pipes to the furnace flanges.

So the next time you have your furnace cleaned by an HVAC service technician make sure to check his work before he leaves your property.

Otherwise you may be putting your home and life at risk!

Sealing furnace duct piping into chimney

For information on Restoring Baseboard Heating Element Covers, see the Restoring Baseboard Heating Element Covers eBook from HomeAdditionPlus.com. The Restoring Baseboard Heating Element Covers Ebook provides easy to understand, step-by-step instructions, on how to restore Baseboard Heating Element Covers so that they look new again. Pictures are included for every key step in the process.

For information on how to maximize a wood stove’s heating efficiency, see HomeAdditionPlus.com’s Installation of Hood over Wood Stove eBook

Related Information


Additional Heating and Cooling Resources from Amazon.com


Free Heating and Cooling Price Quotes with No Obligation!

Fill out our 3-5 minute quick and easy form, and receive a free price quote on heating & cooling from one of our pre-screened and licensed HVAC contractors. This process is free and there is no obligation to continue once you receive your heating & cooling price estimate.