Plenum Box: 5 Things You Wish to Know Earlier

HVAC systems have the potential to offer sufficient airflow throughout a property or building, provided they are allowed to work effectively and efficiently at high temperatures. And this is where a plenum box comes in. The plenum in your HVAC system is significant for the effective function of your heating and cooling system. Located on either side of the heat exchanger or fan, the plenum brings in, circulates, and removes air.

It is the first stop for the air in your home after it is cooled or heated and also the last stop before it goes back into the furnace, AC, or heat pump. To be more precise, plenum boxes are galvanized iron boxes installed just before the fan coil’s cooling coil to reduce the velocity of return air, so the face velocity of the cooling coil does not go above 2.5m/s.

Now, that you know what a plenum box is, here are 5 significant things to know about it:

1. Specific Use of a Plenum Box

The plenum box is at the rear side of the FCU or fan coil unit. However, you can find it at the back of the external air louver or supply air diffuser. For grilles, louvers, and diffusers, it becomes imperative to use a plenum box to connect the duct. Besides, these components also serve the purpose to combine fresh air with return air. Plenum boxes also serve as adaptors for round-to-square duct connections with the duct collars.

2. Types of Plenum Boxes

The two types of plenum boxes in an HVAC system are called the supply plenum and the return plenum. And both are equally important for the system to work efficiently.

The supply plenum distributes fresh air and exhausts unclean air from a building in a controlled and efficient manner. The work procedure of a supply plenum involves receiving warm or cool air from the HVAC and distributing it across all the spaces. The supply plenum is the air’s first stop in its journey before being used for air cooling or heating. Made from steel, aluminum, or cast iron, the supply plenum is located very low outside or inside your home and also features louvers to serve different sections of the house.

The return plenum returns filtered and conditioned air back into the conditioning systems through a series of fans. This plenum receives air from the return vents of the HVAC system, cools or heats it, and then returns the same for proper distribution. It also features an air filter to ensure that the air sucked back into the HVAC system is safe and clean.

The return plenum connected to the return outlet of an AC, heat pump, or furnace is the second stop of air. Cooled or heated air from this component returns to the same ductwork and makes its way through the house to be reheated or re-cooled by another part of the HVAC system in your home.

Be it any plenum box you are using, a few specifications of the unit include:

  • Size: 12x12x12 inches, completely customized as per the customer's requirement.
  • Fuel: Petcoke, bagasse, wood-fired, agro waste-rice, and coal.
  • Dimension: 25mm or 50mm as per the approved drawing
  • Boiler capacity: 1, 000 to 50, 000 kg/hr
  • Surface finish: Powder-coated or simply coated
  • Maximum flow rate: 1, 000 liters per second
  • Frequency: 50 hertz

3. Advantages of a Plenum Box in an HVAC System

You must know that there are several advantages of using a plenum box in your HVAC system. These include:

  • Plenum boxes are good at reducing noise levels. They distribute air quietly and evenly, thus making them perfect for sensitive environments and high-traffic regions.
  • They are one of the best air-cooling sources as they can draw away heat from the areas that are being cooled.
  • They work efficiently to improve airflow in a home or any other property, which reduces humidity levels and creates a very comfortable environment within an office or home.
  • For people with forced-air cooling or heating systems, clean ducts are vital to prevent small particles from getting into your HVAC system. A plenum box can prevent dirt and debris from entering the system and your premises.


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4. Risks Involved In Using a Plenum Box

Since better airflow is an integral part of an efficiently heated or cooled space, it is crucial to ensure that plenum boxes are well-maintained throughout use. If these boxes get blocked, they may fail the entire HVAC system and if you do not install the ductwork properly, it may cause several issues.

5. Fixing a Leaking Plenum is Crucial

Repairing a leaking plenum as soon as possible is crucial as it may reduce airflow into a property. Bad airflow, less conditioned air, and high energy bills are the common causes of a leaky plenum box. And since the conditioned air is not distributed into your home but into the attic, your HVAC system may not be able to work efficiently. You can fix the leakage instantly by using tape to coat the HVAC mastic and get proper sealing. Once the coating on the HVAC mastic dries off, it will seal the leakage. You can add another coat to get a good seal. However, if the entire box is damaged, you may have to replace it.

The Bottom Line

A plenum box is an integral part of the HVAC and is used as an air distribution box. The ducts in this box carry heated or cooled air throughout a building. And if the ducts in this box are not sized properly, it may result in uneven distribution of heated or cooled air throughout a property. Also, damaged or leaking plenum boxes should be repaired or replaced as soon as possible to ensure even airflow within a home.

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