Smoke pens offer HVAC technicians and remodelers a simple and affordable option for finding leaks in ductwork.

The Lone Landlord on Youtube buys homes and renovates them for his tenets, often scooping-up old homes with unfinished basements and poorly assembled ductwork. In an Aug. 2020 video, he shows how he applied water-based mastic sealant to every seam, elbow and screw he could find in the unconditioned space.

He also used foil tape, but suggested the best product for the money is duct sealant, offered by several companies in the HVAC industry. It takes 24 hours to harden, and then it’s best to test for any further holes: "All you're looking for is any smoke to be changed by any air that's leaking out,” the Lone Landlord says.

As HVAC industry veteran Chad Peterson recently explained, one major leak area is duct flex connectors. Flex connecters bring together two sections of duct, or duct and a furnace, and as you close the leaks, the system runs quieter. By turning the fan of the heating system on and introducing smoke along all duct seams and connections, you can find every crack leaking air. 

“The gores (the joint in an elbow) that allow the elbow to turn or adjust are also each, a small leak,” Peterson concludes.