Know before you go:
•Check to see how much of your ductwork is accessible from the basement, crawlspace, or attic.
•Check whether ducts are made from sheet metal, fiberglass, flexible tubing, or a combination of these. Tape works especially well on fiberglass and flexible ducts as well as flat metal ducts; liquid duct sealant provides a tight seal around odd-shaped metal joints.
•Wear eye protection. You’re working beneath dusty ductwork and, in the case of sealant, brushing liquids overhead.
Tape ductwork
Step 1. Vacuum ductwork where possible and wipe it clean with soapy water. Check for any loose fittings that can be tightened.
Step 2. Cut a piece of HVAC foil tape long enough to wrap around the duct at each joint.
GOOD TO KNOW “Duct tape” isn’t for ducts
Cloth adhesive tape sold as duct tape lacks the long-lasting, temperature-resistant adhesive needed for a good seal. Instead, use a foil-backed tape with adhesive that resists heat damage and aging.
Step 3. Peel off the paper backing and apply tape centered on the exposed seams in the ductwork. Press the tape in place using a plastic putty knife.
Make joints airtight with duct sealant
Step 1. Vacuum ductwork where possible and wipe it clean with soapy water. If you find any gaps greater than 1/4", fasten the pieces together again before applying sealant, or cover the gap with flexible mesh tape.
Step 2. Beginning from the top or upper sides, brush sealant onto the ductwork over the joints. Coat the ductwork with bands about 2" wide and centered on the seams. Using the brush, work the sealant into the seam. Allow at least one day for the sealant to dry.
GOOD TO KNOW Look for a low-odor sealant
You can find solvent-based duct sealants, but a water-based product will give your nose and your house a break. As with anything containing even small amounts of solvent, though, provide plenty of ventilation where you work.
Step 3. Spot-seal any screws or openings in the ducts, especially around floor registers and elbows.
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