Description of a Furnace Plenum

Location

• The plenum is considered part of the duct work of the furnace. The heating duct leads to a filter to catch dust and dirt particles, and then proceeds to the blower. After the blower, the duct leads to the burners, an area also called the heat exchanger. The plenum is the next part after the heat exchanger.

Function

• In a dry air furnace, the burners heat the air to a desired temperature and the air proceeds upward to the plenum. The warm air sits in the plenum until the furnace distributes it throughout the home. In a combined water and hot air system, the plenum may sit beside the heat exchanger. The box does not have any parts on the inside nor does it ever need cleaning.

Troubleshooting

• The metal casing of the plenum means it does not need regular maintenance. However, a plenum with a damaged seam could leak air. The leak will cause the furnace to work harder to maintain a comfortable home temperature. The seam must be repaired to avoid high energy bills. In most cases, a professional can repair the seam.

Reaching the Plenum

• A repair job means the plenum must be disconnected, and it could involve the disassembly of the furnace. Depending on the model, the burners may need to be removed to reach the box. There is no way to know if the seams are leaking without a physical inspection. However, if duct work and other furnace parts are not the problem, it is prudent to inspect the plenum.