What Is the Purpose of an HVAC Phelum?

Return Air

• Of the three main components of an HVAC duct system, return air, blower/handler and supply air, the first component is the return air. A return air phelum is an enclosed chamber that collects air from the individual rooms of a home. In some instances, it may also collect fresh air from outside. Filters typically clean the air inside of the return air phelum before sending that air to a handler or blower. Depending on the specific HVAC system, moisture may be added to the return air inside of the phelum as well.

Receiving Air From a Blower/Handler

• After air passes through a return air phelum, a blower or handler either adds or removes heat from the air, depending on what is necessary for making a home comfortable. In older HVAC systems, the blower or handler -- as opposed to the return air phelum -- is also responsible for filtering the air. Once the blower or handler treats the air, the air is transferred to a supply air phelum. Unlike a return air phelum, which is responsible for collecting untreated air, a supply air phelum is responsible for collecting treated air.

Delivering Conditioned Air

• In addition to collecting treated air from an HVAC system’s blower or handler, a supply air phelum delivers that air to the individual rooms of a home. There are two main varieties of supply air phelum: central and extended. With a central phelum system, all of the branch ducts, which reach out to individual rooms, start at the same, centralized location: the phelum. In contrast, with an extended phelum system, the phelum is connected to an outlet. Main supply ducts connect to this outlet and then stretch along the length of a home. Branch ducts, instead branching out from the phelum, branch out from the main ducts.

Housing the Mixing Box

• Also known as a VAV box, a mixing box regulates the amount of supply air that an HVAC system delivers into a home’s spaces based on a home’s heating or cooling needs. The lines from a home’s thermostat feed into the mixing box. In addition to collecting and delivering treated air, an HVAC system’s supply air phelum is typically responsible for housing the system’s mixing box.