How to Fix a Leaking Air Duct

What You'll Need
Mastic sealant
Duct tape
Panduit strips
Fab mesh
Caulk mastic
Caulk gun
Putty knife
Foil tape

Air duct leaks are undesirable to homeowners because they cause temperature issues, and waste money as well. The more air that is lost through a leaking duct, the less that it is cooling your space, the longer the system has to run to meet its temperature requirement. If you can gain access to your ducts, you can fix them yourself. 

Step 1 – Check 

Turn the thermostat fan switch to ON rather than AUTO. Proceed with your examination of the duct work, looking for leaks and loose connections by feeling around all the joints and connections. Flexible ducts can come unfastened or tear over time but you can repair them. 

Step 2 – Loose Flex Connections

Flexible duct reparation starts with loose flex connections. If it has fallen off entirely, remove the old Panduit strip. The Panduit strip is a plastic zip tie that keeps the inside portion of the flex tube in place. There might be one on the outer layer as well; remove it. Pull the outer layer and the insulation back, unearthing 8 to 12 inches of inner layer. Fit the inner layer into the boot connection and use duct tape to set it into place. Attach a new Panduit strip with pliers. Pull the outer layer down and attach a Panduit strip to it. Do the same on the outer layer. Using your paintbrush, paint the connection with mastic sealant. 

Step 3 – Ripped Flex 

If you discover torn flexible ducts, first clean them. It is easier to get a good seal on a clean surface, though it doesn’t have to be immaculate. Draw the rip together. Hold it in place using duct tape. Extend a piece of fab mesh over the seam and paint the fab using mastic sealant. Apply the mastic sealant generously and let it cure for about 10 minutes. You can do this in the opposing order, applying sealant and then covering it and overlapping the bare duct with mastic tape. For seams that just will not comply, use a staple gun to hold them in place. Fill large gaps with insulation before you apply fab and mastic sealant. 

Step 4 – Wait and Test

Wait before you test out the unit. Turn it on again and feel to see if you’ve solved your leaking air duct issue. If you feel nothing in the patched spots, you’ve successfully done the job. 

Step 5- Sealing Heat Ducts 

Turn off the HVAC power to avoid bubbles in the caulk. Caulk the seams and joints of your duct work using caulk mastic. Use a putty knife to adequately cover the seams and joints. For areas you cannot get your caulk gun into, use foil tape; its acrylic adhesive will bond better than duct tape. Check the caulk tube to find out how long it needs to cure before you turn the power to your HVAC unit back on.