Sheet metal is commonly used for heat and air conditioning ductwork. The main line has smaller branch feeder trunks, connected with takeoffs. Elbows, offsets, reducers, wyes, T-plugs, and log boots are used to align and connect ducts. Return air ducts may use panning. Dampers regulate airflow, and joints must be sealed with putty or adhesive.
Installing heat and air conditioning ductwork requires a variety of duct supplies. These channel supplies are most commonly made from sheet metal. The trunk main line is a rectangular duct and is joined with chutes and transmissions. Hooks on the duct can be made from 1 inch (2.54 cm) sheet metal strips. A plenum is a fitting used to connect this main line to the furnace.
The main line of feeder pipe will have smaller branch feeder trunks coming out of it. These branches will deliver air with each log opening. Branches are usually rigid, round tubing, but can also be made from flexible fiberglass duct. They are connected to the main line with a takeoff.
A takeoff can be rectangular or round and fits into a hole drilled in the ductwork. It has tabs on the end that need to be folded into the duct. This keeps the takeoff firmly in the duct. When using flexible conduit, nylon straps must be used to secure the conduit to the takeoff.
The main branch feed lines will run to each of the register openings. Elbows or offsets may be required to align the duct in the right spot or to avoid obstacles in its path, and sometimes a reducer must be used to replace the round duct with a smaller sized duct. A wye can be used to supply air from a two port branch duct. A T-plug closes the end of a piece of round tubing. A log boot is nailed into the opening and the branch duct will attach to that; the registry is then inserted into the boot.
The return air duct uses the same supplies as the sheet metal duct. Sometimes, in an effort to reduce costs, no ductwork is used for all return air; panning is used instead. The panning material is sheet metal or foil-covered cardboard type that is installed on the joist space and stud space. This creates a tunnel for the return air to pass through. A return air elbow is usually used to connect the return air duct to the furnace.
Additional duct supplies may be required to achieve a balanced heating and cooling system. Manual or electronic dampers can be inserted in the duct to regulate the air flow. All joints must be sealed with a special putty or duct adhesive. Special aluminum tape also works well, but don’t use duct tape. The ductwork must be sealed during assembly.
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