The Plenum Kit 20 X 20 X 36 is designed to house Goodman CAUF and other uncased A coils up to 21” inches in width. The design of the plenum takes up very little space and is easily transportable. To install, simply measure and cut to size using tin snips to match the supply opening of the evaporator coil. The plenum comes with four trimmable sides and one trimmable top. This plenum kit is not meant to be used with a furnace.