How to Repair Holes in HVAC Ducts

Turn off the HVAC unit.

Put on your safety glasses.

Wipe the area around the hole in the ductwork with a clean rag to remove dust, dirt, and contaminants from the duct's surface.

Measure the height and width of the hole in the ductwork with a tape measure.

Add 1 inch to both the height and width measurements, and use a permanent marker to place a mark for each dimension on a piece of 26 gauge galvanized sheet metal.

Extend the height and width measurements by aligning the blade on a combination square with each mark and drawing a line along the blade with the permanent marker. Make sure that the two lines intersect.

Cut along the lines with aviation snips.

Place a 5/16-inch hex head screw adapter into the chuck of the variable speed drill motor.

Set the cut piece of 26 ga sheet metal against the side of the ductwork and run a #10 self-tapping sheet metal screw into one corner of the metal patch, if you are installing the patch on metal ductwork. If you are installing the metal patch on fiberboard ductwork, place a length of metal foil tape on each side of the metal patch to secure it to the ductwork.

Continue placing #10 self-tapping sheet metal screws at each corner of the sheet metal patch to secure it to the side of the ductwork.

Open the end of a tube of silicone caulk by cutting the nozzle of the caulk tube at a 45-degree angle with a utility knife. The opening of the nozzle should be 3/16-inch in diameter.

Puncture the inside of the tube of silicone caulk by sliding an eight-penny nail into the nozzle until you feel it push through the membrane located at the bottom of the nozzle.

Place the opened tube of silicone caulk in a drop-in caulk gun.

Run a continuous bead of silicone caulk around the perimeter of the metal patch to seal the patch to the ductwork. If you have installed the patch on fiberglass duct board, smooth the tape with a plastic squeegee to seal the metal patch.

After the silicone caulk has had time to set, turn on the HVAC unit. If you installed the patch on fiberglass duct board, you can immediately turn on the HVAC unit after you smooth the metal foil tape.