The plenum, or trunk line, is what comes directly off of the air handler and is what the supply tubes connect to. Plenum can be used in several different ways. In most installations, round metal plenum is used in 178mm, 229mm, or 254mm diameters, depending on the size of the system. This is then wrapped in an insulation sleeve to prevent thermal loss and most importantly to stop condensation.
Unico, Inc. also manufactures our own plenum. This is a fiberglass square plenum that features ship lap connections, making installation a breeze. We manufacture the plenum in 183mm sections available in 165mm, 216mm, and 241mm square dimensions, depending on system size. In addition to the 183mm straight sections, we also offer a full range of components that includes elbows, tees, reducers and end caps.
A lesser used option is to use rectangular plenum. This option is typically done in installations where their is no room for round or fiberglass plenum and the installing contractor needs to make their own plenum. To view sizing requirements, see below for Bulletin 30-45.