Leaking or poorly insulated ducts are a common and serious problem in forced air systems, affecting comfort, health, and economy.
Start by inspecting all of the ductwork in your system. If you find places where the duct was never installed or connected, or has broken free from the adjoining duct or register, call a competent contractor immediately. Such failures are murder on system performance and can pose a health hazard. If you find a seam where the duct tape has peeled away, strip off the old piece and reseal it with duct-sealing mastic, a sticky compound you apply with a putty knife.
Any duct that runs through unconditioned space, such as an attic or garage, should be wrapped with a blanket of fiberglass that has an insulation rating of R-11 or better. If you plan to have your system pressure-tested and sealed by a professional, wait till that work is completed before you insulate the ducts.
Seal the ductwork with caulk at any points where it penetrates an exterior wall, floor, or ceiling.
Remove each supply register and vacuum out the inside of the duct. You can hire a pro to do a more thorough cleaning, but avoid firms that use glue-like materials to “seal” dust inside the ducts. These products may contain formaldehyde or other harmful air pollutants.
If your system has an air filtration device and/or humidifier built into the ductwork, take special care to follow the manufacturer’s cleaning and maintenance instructions.

Money-saving tip
For $200 to $400, you can hire a contractor to do a flow hood or blower door test on your ductwork. The test will reveal the total amount of leakage in the system and pinpoint where the leaks are. Once the system is professionally sealed and balanced, you’ll enjoy better comfort and economy.

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