What Is A Plenum In HVAC System?

You might be wondering what a plenum is in an air conditioning system and a lot of times it isn’t described properly.

A plenum is often confused with other parts of heating or cooling systems, so I’m glad I have the opportunity to describe everything to you.

There’s a lot more that goes around plenum, but let’s first talk about what exactly a plenum does and what’s its role in the whole process.

What Does The Plenum Exactly Do?

A lot of times people don’t have a clue what plenum is because it’s rarely spoken about.

It has a ton of different meanings, but in the cooling and heating world, it comes to the same one – airflow.

Plenum is simply an air distribution box specially designed to push as much air as possible in heating or cooling systems.

Plenum also handles the air which enters the ducts and recirculates it immediately.

Two Types Of Plenum

There are two different types of plenums in our air conditioners.

Return plenum – The first one is the return plenum and as you might have guessed, it returns the air back into the system. You can easily find it as it’s located just near the air filter.

Supply plenum – It’s located at the beginning of the ductwork and it supplies the plenum with air that’s being spread throughout the home. In most cases, central heating and air units have a supply plenum.

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How To Maintain The Plenum

The return plenum is a lot easier to maintain and clean because you can find it within a few seconds.

On the other hand, the supply plenum can be hard to access in some units, but once you get used to it, it’s not that big of a challenge.

The rule of thumb says to clean or replace the filters in the plenum once every 3 months. 

Of course, the ideal would be to clean it every month, but if you don’t have that much time, you can do it once every 90 days.

It has a big impact on airflow, so pay attention to it.

Even if you maintain it often, it might come time for these air distribution boxes to reach their limit – so you might need to buy a new one.

Also, always maintain them with care as plenums can easily be damaged if it’s bumped or moved hard.

How Much Does a Plenum Box Repair Cost?

Plenums usually cost anywhere around $100-$350 depending on the size and technology.

However, installation costs can pretty quickly add up as they’re around $500. You can alternatively buy plenum duct board kits that don’t require professional installation but are far less durable.

I need to point out that plenum installation isn’t an easy task and that I always recommend seeking professional help.

As for repair costs, if your plenum isn’t damaged or broken – it should be around $100-$150.

The bad side is that once plenums need repair, they’re usually well-damaged and you’ll have to buy a new one.
If your plenum is already damaged and your AC isn’t performing at this moment, here are quick ways to cool down a room without an air conditioner.