Duct HVAC systems improve the quality of the air, usually by circulating air through the ducts and throughout a home or office building.
Several components are used to move air through the system, including ducts, plenum, return air, vents, and more.
What is a Plenum in HVAC?
A plenum is a metal box that air is sent to and distributed throughout a home.
The box can be both for return and supply air but usually refers to the supply side.
The air flows from the air conditioning unit into a large box called a plenum which will then have duct going to vents.
The ducts need to be sized correctly to get the right amount of air to each room; otherwise, the building will not be cooled or heated evenly.
For example, 5-inch ducts are often used for a small room such as a bathroom, while a living room can use 8 to 12-inch ducts.
Holes are cut into the plenum for the correct sized duct to be connected and run to the room it is matched for.
If the ducts are sized wrong, one room will get more conditioned air than another, causing different temperatures throughout a home.
If the ducts are too small, not enough air can flow in, which can also cause issues.
The air distributed from the plenum must be sized correctly to get the best results.
There can be both a supply and return plenum box, but usually, it is the supply box when referring to a plenum.
Where is a Plenum Located?
A supply plenum is usually located in the attic and will have many ducts connected to it.
While the attic is the most common location, it can also be located in a basement.
If the vents are located on the ceiling, the plenum is likely located in the attic, and if the vents are located on the floor, the plenum is likely located in the basement.
For those referring to the return air plenum box, it is usually located in a hallway or the bottom of a furnace.
How To Fix a Plenum that is Leaking
If you have a supply plenum that is leaking, it will need to be repaired; otherwise, airflow will be reduced into a home.
Common causes of a leaky plenum include less conditioned air, bad airflow, and high electricity bills.
Since the conditioned air is not flowing into a home but into the attic, the system will not work correctly.
A common method of fixing a leaky plenum is to use tape and then coat it with HVAC mastic to get a good seal.
The first step is to tape the spot that is leaking.
Once it is taped, use a paintbrush to coat HVAC mastic on the location, which, once dry, will seal the leak.
After the HVAC mastic dries, another coat can be added to get a very good seal.
If the box is very badly damaged, it may need to be replaced or new metal attached to fix it.
Summary
A plenum is used in HVAC as an air distribution box.
The box can be both for return and supply air but usually refers to the supply side.
It will usually be located in the attic and have many ducts flowing from it, which carries the air into the rooms of a home.
If the ducts cut into the box are not sized correctly, a home will be heated and cooled unevenly.
If the box has a leak, it can usually be replaced with tape and HVAC mastic.
When a box is badly damaged, it may need new metalwork attached, or the box may need to be replaced.