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What Is a Plenum?

If you’ve ever had work done on your furnace or air conditioner, you may have heard your contractor mention a problem with or relating to something called a “plenum.” No, it’s not a made-up word created to upcharge you! The plenums in residential HVAC systems serve very important functions. Read on to learn more about this vital component of your home’s heating and cooling.

What is a plenum box?

In residential HVAC, plenums are more accurately referred to as “plenum boxes,” which form a crucial part of the ductwork in any forced air system. Generating hot or cold air is only half of your AC, furnace, or heat pump’s job. Once it has heated or cooled the air, it must then move that air through ductwork, circulating it through your home. After the heated or cooled air circulates through your house, it comes back to your HVAC unit, which draws it in to heat or cool it once more. Plenum boxes are usually situated on either side of the fan or heat exchanger and have the important function of bringing in, distributing, and removing air. They are the air’s first stop after being heated or cooled and its last stop before going back into your AC, heat pump, or furnace. Almost all systems have two plenum boxes: the supply plenum box and the return plenum box.

What is a supply plenum box?

The supply plenum box connects to the supply outlet of your furnace, heat pump, or AC unit. It receives the newly heated or cooled air directly from the unit, then distributes it to your ducts to be circulated through your home.

What is a return plenum box?

The return plenum box receives used air from the return vents and distributes it to your HVAC unit to be heated or cooled again. The used air must pass through a filter before entering the return plenum, ensuring that it’s clean before it reenters your AC, heat pump, or furnace.

How much does a plenum box repair cost, on average?

While plenum boxes themselves are not particularly complicated, there is labor involved to access, extract, repair/replace, and reinstall them correctly. The cost of a plenum box repair depends on a few different factors: whether it is the return or supply plenum, what state the unit is in, and whether your technician discovers any other issues. If a plenum box is the only repair needed, you can generally expect to pay anywhere from $200-$500.

Choose a trustworthy professional for plenum repair

Plenums are deceptively simple, but incorrect installation can cause big problems for your HVAC equipment. If a plenum is installed in a way that does not allow for smooth airflow, you might end up with frozen direct expansion coils, tripped furnace limits, failed heat exchangers, and failed compressors. You can also lose a great deal of efficiency if air is leaking from your plenum boxes. Having installation or repair done only by a skilled HVAC contractor will ensure that your plenum boxes are set up to do their jobs without fail.

At Air Experts, our NATE-certified technicians pay special attention to this vital component of your HVAC system, making sure that it’s installed and sealed for maximum efficiency and minimum stress on your system. When you need HVAC repair, trust Air Experts for the best possible outcome.

If you have a plenum problem, call 919-480-2727 or contact us online for quality HVAC repair in the Raleigh and Durham area. Our NATE-certified technicians are standing by to provide superior service!

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