6 Common Residential Duct Fittings

Elbows

• Necessary for 30-, 45- and 90-degree turns, elbow fittings come standard in either a 24-inch or a 48-inch diameter. Elbow fittings can be purchased with a flanged end or a raw end. For systems that require a minimum of leakage, non-welded fittings with a pleated flange is recommended.

Y-Branch Fittings

• Y-branch ducts serve to change a single airflow into two streams. The fittings are available in 30- or 45-degree angles, with 24- or 48-inch diameters. A variation on the Y-branch fitting is the diverter fitting that has the similar "Y" shape, but the air flow can be sent to both outlets or be manually or automatically diverted from one branch to the other.

Reducers

• A reducer fitting serves to connect a larger duct with a smaller one. Reducers are often used from a main line to a branch line to reduce the duct size it possible to maneuver through walls. Like most fittings, common thicknesses for reducers are 16 or 18 gauge.

Flanges

• Used to join two ducts together, flanges are also known as angle rings. Most flanges look like metal ring with a square flat surface at one end. Two flanges can be used to join ducts, or the flange can be bolted to a hard surface. Most flanges have pre-drilled holes for easy installation.

Plenum

• A box made from sheet metal and attached to an air handler or furnace outlet, the plenum is a central manifold that services the ductwork. Designed to encourage air movement, plenums come in a variety of sizes, determined by the size of the air handler.

Stackhead

• A stackhead or stackhead boot is an end fitting that looks like a large vacuum cleaner attachment. Used at the end of a line, the stack head terminates in a rectangular opening in a wall, floor or ceiling. A register or vent grating is placed over the stackhead opening to direct or restrict airflow into the room.