How to Add an AC Duct

Measure the height of the existing duct work and make sure that it is taller than the new duct work that you're adding. Mark out the perimeter of where you will cut the hole for the new duct work.

Cut a hole with the jig saw in the existing duct work that is closest to the room where the new air conditioning vent needs to go. Cut it so that the new ducting will be able to slip inside the existing duct by ¼ inch. Check the hole for the proper fit.

Secure the duct hanger to the floor boards using a drill and 1-inch wood screws along the path of the new duct.

Check the floor where the hole for the vent will be to ensure there aren't any electrical cables in the way. Cut a hole in the floor that is large enough to accommodate the vent cover.

Position the angle ducting so that it covers the opening in the floor and angles back toward where the rest of the ducting will go. Secure the flashing around the angle duct work to the floor boards. Slide the other end of the angle duct work into a duct hanger.

Slide one end of the straight duct work into the hole that you cut into the existing duct work.

Slide the straight duct work onto the end of the angle duct work until the two pieces fit together securely. If necessary, slide the straight piece back farther into the existing duct work to provide the room needed to fit the two pieces together and then move the straight piece of duct work back out as the straight duct work and the angle duct work become fitted together.

Position the new duct work into the duct hangers.

Seal all seams in the duct work with the aluminum duct tape. Place the tape along the seams where the pieces of duct work join together and where the angle duct work attaches to the floor boards.

Position the new vent over the hole that you cut in the floor and secure in place with a drill and the screws that are included with the vent.