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What is a Return Vent?

By Eric Tallberg
Updated May 16, 2024
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Every home and building that uses forced hot air for heating purposes will have return vents. The return vent, or register, is also known as an air return vent, and a cold air return vent. It accomplishes just what the various names imply, return colder air, via registers and ductwork, to the furnace so that it will run as designed. Return vents also provide proper air circulation throughout the structure. A return vent, will, as well, be installed with central air conditioning systems, though in a somewhat different configuration.

Air return vents are necessary to prevent a buildup of pressure in the structure that may lead to various health problems, as well as preventing mold and mildew, and deterioration of the structure due to moisture buildup. As warm air is forced into a room, it replaces cold air already in the room. This cooler air must be pushed out of the room; otherwise the room becomes uncomfortably over-pressurized. The cooler air is, in turn, forced into the return vent, back to the furnace, reheated, and returned to the cycle.

The size, location, and length of heating, ventilating, and air conditioning (HVAC) registers and ductwork are determined by measurement of air movement at cubic feet per minute (CFM). Whatever the CFM output of the heating or cooling system, the air return vents must be able to provide the same CFM ratio. Additionally, for maximum heating and circulating efficiency, there should be properly-sized return vents in each room where heating registers are located.

Heating and air conditioning registers are located on the outside walls of structures, air return vents on the inside walls. This is because the warmed or cooled air at the outside perimeter of a room forces the cooler or warmer air already in the room toward the center of the structure. From there, cooler air is circulated via return vents to the furnace for more efficient operation. In the case of air conditioning, the warm air in the room is forced to the return register, and vented outside the structure.

Unfortunately, most homeowners are unaware of the importance that a well-designed, properly-functioning air return system has in assuring correct air circulation. Maintaining the return vent, or vents is very important, however, and often a matter of simply unscrewing and removing the grille, vacuuming inside the return register, and inspecting duct seams. Additionally, an unsightly grill can be repainted, or replaced just as easily. Assuming a properly designed installation, and timely maintenance/cleaning, a return vent system will be attractive and fully functional for many years.

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Discussion Comments

By anon957607 — On Jun 21, 2014

We have a new build home and have high humidity problems. Our builder says there is not a problem but humidity in the high 60's and 70's in wrong. the house is cold and humid starting in the spring and lasting through the fall.

The builder says the heating/air system is working like it should. they have checked the system and the floor vents and found no problem. We live on a slab and they have checked under it and find no water build up. Where do we go next? It is very uncomfortable and the wood in the house swells. Please help.

By anon944195 — On Apr 06, 2014

The return air flow is one location in the house; it is not the air vents that blow out the air. Instead, it sucks up the air and returns it down the ducts to the air vents to be blown out again. I hope all these people who say they don't know what that is have been opening that up and replacing the air filter in it around once a month or so, or their air units will not be any good after a while. No, never cover up the return air vent, or you will burn up the whole air conditioner inside the house. The air has to be pulled up through in order to exchange it.

By kookykook — On Feb 17, 2013

The return air duct in our house has a thin pad of insulation spot-glued to the inside walls. It is really nasty and I'm concerned about health risks because of it. Does it serve any purpose and what would you suggest I do to remedy the situation?

By cloudel — On Feb 17, 2013

@seag47 – It all depends on how filthy it is. I wouldn't replace it just because the label says it's time to do this.

I remove my return vent grill once a month and vacuum out the filter and the vent. I suck out all the dust in between the slats on the grill. This seems to make the filter last longer.

I have a filter that also is supposed to remove allergens from the air, so once it gets really dirty, it is important for me to replace it. Otherwise, I'll start sneezing and wheezing. I never go by the recommended time on the label, though.

By seag47 — On Feb 16, 2013

How often do I need to replace my return vent filter? The label says I need to replace it once a month, but it really doesn't look all that dirty yet.

By orangey03 — On Feb 15, 2013

I have always wondered what that large vent was in my hallway. I believe it is the air return vent after reading this article.

I never could feel any air coming out of it, so I didn't know what it was for. Thanks for clearing that up!

By anon312267 — On Jan 06, 2013

Can you put a couch right in front of an air vent return? Not flush against it but right in front?

By anon301703 — On Nov 05, 2012

I've never seen a house or apartment with central heat that has return vents. Each room has only one vent, which only blows the hot or cold air in. I think return vents are a myth, not that they don't make sense, but that in the U.S. nearly all builders save a little by not including them.

By anon290294 — On Sep 08, 2012

I had seen a home repair show in which it was stated that covering the returns while the central air conditioning is running is more economical. What are you thoughts on this? These vents are on the floors and low on the walls throughout the house.

By anon278664 — On Jul 08, 2012

With an interior heatpack unit and attic/ceiling delivery ducts, for the most efficient operation, should the return air vents be located near ceilings (warmer air) or floors (cooler air) for the summer cooling operation? What about for the winter heating operation?

I respectfully request only responses with factual, absolute answers (thermodynamic understanding) - please, no anecdotal information. --John H.

By AngelChaser — On Feb 09, 2011

Another way to think of a return vent is being similar to a your nose or mouth when you breathe, except in this case the return vent isn’t necessarily getting rid of carbon dioxide, it’s getting rid of the warm or cool air already in the house.

By PandaGolden — On Feb 07, 2011

@anon79439 - The direction of the air vent doesn't matter, except for aesthetic purposes. If you don't want to see the inside vent, point them up.

By anon79439 — On Apr 22, 2010

which direction should these vents be inserted --up or down? i am always confused when i take them out to clean.

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