Return air comes through return grilles, ducts, door undercuts, transfer grilles or a ceiling plenum. An undersized or missing return path starves the blower, raises static pressure, and pressurizes closed rooms, pushing conditioned air out through the walls. Return air temperature and humidity are the baseline readings for any cooling or heating diagnosis.
Bedroom doors closed and there's no return in there, so the rooms pressurize and the hallway return gasps for air.
An undersized return is a classic hidden defect in residential systems; check it before blaming the equipment.
Also heard as
- RA
- return
Related terms
Plenum
A box on the supply or return side of an air handler that feeds or collects several ducts, or a ceiling cavity used as a return path.
Building pressurization
Controlling the air pressure inside a building relative to outdoors, usually by bringing in more outdoor air than is exhausted.
Economizer
Dampers and controls that bring in cool outdoor air for free cooling instead of running compressors.
Static pressure
The pressure air exerts outward on duct walls, the resistance a fan works against, measured in inches of water column.