What Is a Plenum (And Why Is It Important)?

When changing the air filter in your HVAC unit, you’ll probably find it between the two plenums. Or, if you’re having difficulty with air flow coming from your air conditioner or furnace, the HVAC technician may say something about replacing the plenums. So, what is a plenum? Our air conditioner repair company is answering this question, explaining why they’re important and how to know if yours may be malfunctioning.

What Is a Plenum?

The plenums, or plenum boxes are responsible for moving heated and cooled air through the house and back through the unit. Nearly all HVAC units have two boxes, the supply and return.

Supply Plenum Box

The supply plenum box is connected to the supply unit of the furnace, air conditioner, or heat pump. Once the air is heated or cooled, it goes into the plenum box and is then moved into your ducts and through your home.

Return Plenum Box

After the air has circulated out through the vents, it can be pulled back through the return vent to be warmed or cooled again. The air goes through the air filter into the return plenum box, and is then warmed or cooled and sent back into the supply plenum to the ducts.

Signs of Problems with a Plenum Box

The plenum box is more of a storage container for air as it moves into and out of the unit, so having the proper size box along with air hoses at the proper angle going into the boxes is necessary to keep air flowing as it should. For example, if the duct going into the return plenum is at a sharp angle, the air will slow to a halt and won’t properly flow into the filter then into the plenum box.

If the plenum box is the wrong size or isn’t connected efficiently, you may experience frozen coils or a malfunctioning heat exchange. Try changing the air filter first because if it’s clogged, air can’t move into the return plenum box. If it’s clean, the ducts may need to be professionally cleaned or the box itself may need repaired.

Can I Replace a Plenum Box Myself?

If your plenum box has failed, you may want to save some money by repairing or replacing it yourself. While the component doesn’t look complicated, if it’s not installed properly to allow proper air flow, your unit’s coils can freeze, the furnace can trip, and over time the compressor itself may malfunction. Relying on a certified, experienced HVAC technician for plenum box repair and other heating and air conditioning repair will ensure the job is done correctly and your system can keep your home warm or cool as you need it.

Schedule AC Repair Service in Garner Today

If your furnace, air conditioner, or heat pump isn’t working as it should – it keeps freezing up, overheating, or there’s diminished air flow – and you’re concerned about the plenums, call our experienced team. We have proudly served Garner, South Raleigh, and the surrounding area for over 40 years and will have your HVAC system running smoothly in no time. Schedule service today by calling  919-772-2759 or filling out the form below.