Sealing Heating And AC Ducts To Save On Energy Bills And Protect The Air Quality In Your Home

If the ducts in your home's HVAC system aren't sealed properly, much of the heated or cooled air that travels through them doesn't arrive at its intended destination. Inadequate sealing of ducts also creates an opposite effect.

When air is not being forced through the duct system, moisture can enter the ducts. Mold grows wherever there is moisture to sustain it. This mold can not only inhibit air flow, but the mold spores can also be blown through the ducts, causing potential health problems for the elderly, children, and anyone in the home with compromised immune systems or allergies.

You can seal any accessible ducts (those not hidden inside walls and ceilings) yourself with a minimal amount of skill and supplies. 

What you will need to seal your ducts

Caulking gun

You can choose either a large or small caulking gun, depending upon the type of tubes of duct sealer that you intend to use, your arm and shoulder endurance, and the area around the ducts.. Smaller caulk guns are lighter to hold in place as you apply the duct sealer, but the tubes must be replaced more often. Larger caulk guns are heavier and more difficult to reach less accessible areas of the ducts.

Duct sealer

Use only a water based duct sealer inside the home. Solvent based duct sealers are highly flammable and emit dangerous and unhealthy fumes, and they are not necessary indoors, where wet conditions are not present .

Duct seal brushes

These are small round brushes that have a brush head with a perfect width to form a consistent bead of duct sealer along long seams and are flexible enough to seal the corners in duct connections, which are problem areas for air leaks if not sealed well.

Foil duct tape

Although the traditional gray duct tape has many uses, sealing ducts is ironically not one of them. Foil tape provides a much better seal, and doesn't degrade into strings and dust as less expensive gray duct tape.

Applying duct sealant with a caulk gun

Caulk guns have a small opening beside the handle and squeeze trigger for cutting off the tip of a tube of sealant. Place the tip of the tube inside the opening and squeeze the trigger to remove the tip. There is also a long thin rod that swings out from the bottom of the caulking gun. This rod is inserted into the tube opening creating by removing the tip. Push the rod until the plastic seal inside the tube is breached, and you're ready to seal.

One side of each length of duct has a 1/4" fold of metal, which is a seam that holds the length of duct together. Place the tip of the tube against the seam and squeeze the trigger as you move the tip down the length of the duct.

When you have a bead of sealant along the length of the duct, use the duct seal brush to smooth the bead into a consistent width and depth. Add a dab of sealant to any point along the seam that looks thin, and smooth it with a duct seal brush.

You will then apply it along the edges of the slip and drive connectors at each end of the ducts, smoothing the bead of sealant as you apply it. You will then add additional sealant to the corners of each duct connection, brushing it to completely cover any gaps.

Applying foil duct tape

After the duct sealer is dry to the touch, you will apply the foil tape along the lock seam of each length of duct, then around the slip and drive connections between each length of duct. The foil tape is not easy to tear, so scissors would be a great help.

Applying both sealant and foil tape will double the effectiveness of the sealing and keep the treated air in and the moisture out of your ducts. For more information, visit websites like