An Overview of Furnace Plenums: Functions, Types, and Associated Problems

Many homeowners do not have a thorough understanding of their HVAC systems. This limited understanding is just one reason HVAC professionals should handle all HVAC problems. For example, few people know what a furnace plenum is, even though it is vital to their HVAC systems.



Below is an overview of furnace plenums.

A furnace plenum is an air-distribution box. A typical furnace has multiple ducts, all of which air flows through. The plenum is an enclosed box that receives and distributes air through the ductwork.



Your furnace has two plenums: supply and return.

The supply plenum connects the supply ducts to the furnace's outlet. The furnace blows warm air into the supply plenum, which then distributes the air through the supply ducts. The supply ducts then channel the warm air into different parts of the house via supply vents.



The supply plenum also has a limit switch that monitors air temperature. The switch sends temperature feedback to the main control board that controls the furnace operations. The temperature feedback is necessary for two main reasons.

First, the control board uses the feedback to shut down the furnace if plenum temperature rises to dangerous levels. Secondly, when you switch on the furnace, the control board uses the signals to switch on the air handler once the plenum temperature reaches comfortable levels.

The return plenum connects the return ducts to the furnace's air intake. The return air ducts passively receive stale air through the return vents. The air then flows through the different return ducts, which channel all the air into the return plenum. The return plenum usually has an air filter that cleans the air before it reaches the furnace. However, the filter may be located between the two plenums or inside the supply plenum.



The supply and return plenums handle all the air circulating in your house. This critical role means that a problem with the plenums can affect your house's entire heating efficiency. Below are some of the problems that might affect the plenums.



The filter cleans the air that enters the furnace to prevent it from clogging. Dirt is dangerous for your furnace since:



• Filter clogging restricts airflow, which impedes heating and leads to uncomfortable temperatures.
• Clogging increases the risk of poor indoor air quality if some debris manages to reach your indoor air.
• Dirt on the furnace increases the risk of fire outbreaks.
• Dirt increases the risk of mechanical damage to moving parts due to increased friction.

Clean or replace the filters regularly to prevent such problems. Ensure you use the right filter for maximum efficiency.

The furnace won't get the correct temperature feedback if the limit switch malfunctions. A malfunction can cause your furnace to overheat or your plenum to supply you with cool air during the cold season.



The plenum is a mechanical contraption, so it can suffer mechanical damage. For example, cracks may develop in the plenum after many years of use. A plenum can also dissociate from its duct attachment. The plenum will leak air in either case. Air leakage means both the furnace and your house won't get the air they need.



Contact Central York Corp if you suspect a problem with your HVAC system. For example, you should contact us for a diagnosis and solution if your furnace blows cold air or makes strange sounds. We have nearly 50 years in the HVAC industry and pride ourselves on honesty, integrity, and trust. Contact us for a free quote on our HVAC services.