Return Air Duct – What Is It and What For?

Many people have heating, ventilation, and air conditioning (HVAC) systems in their home but aren’t quite sure how it works behind the scenes. One essential part of an HVAC system is the return air duct. Why is it an important part of your HVAC system? 

Return air ducts are part of a heating, ventilation, and air conditioning system. The ducts remove the air from a room and send it through a vent to the central unit, where the air is heated or cooled. Return air ducts help circulate air through a building. 

In the rest of this article, I’ll answer your questions about return air ducts so you can better understand the system that circulates air through your home. I’ll also compare supply and return ducts and explain the differences. Let’s get started! 

What Are Return Air Ducts?

Return air ducts are air passageways that pump air out of a room and into an HVAC system. Once the air is returned to the HVAC system, it will be re-heated or re-cooled and then sent back into the home through a supply duct. 

Return air ducts are an essential part of HVAC systems. Without them, the air wouldn’t circulate properly through a building and wouldn’t be heated or cooled to a comfortable temperature. 

The duct is typically hidden, but you can usually see where it begins by looking for vent grates in the wall, ceiling, or floor. Often, these vents are in a hallway or ceiling because they’re most effective in these locations. 

Return ducts help maintain a comfortable temperature in a building and cycle air through a filter, which helps remove contaminants, dust, and allergens from the air, and promotes better health and air quality. If you want to test your air quality, I suggest reading my article on how an air quality test is performed.  

The size of return air ducts is an important component, as they must be big enough to transport air back to the HVAC unit. If the return air ducts are too small or narrow, your airflow will be restricted, and it’ll be harder to get the building to your desired temperature. For more information, check out my article on how to fix HVAC airflow.   

Another important function of return air ducts is maintaining air pressure throughout the building. An HVAC system blows air into the building, and without a return air duct, that excess air would have nowhere to go. If the air pressure in a building is unbalanced, the excess air may be pushed outside, which doesn’t help maintain the desired temperature. 

For return air ducts to work as they should, they must be unobstructed. There shouldn’t be any furniture or clothing in the way that blocks the duct’s ability to pump air out of the room. 

Return air ducts also work better when they’re sealed. To prevent air leaks, you should seal all the connections with a sealant or metal tape. Air duct sealing also prevents dust and other harmful particles from entering the HVAC system. 

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You can use caulk to seal the gaps around your return air duct. Gorilla Store Waterproof Caulk & Seal from is an excellent product because it effectively seals water, air, and moisture. An added benefit is that it is available in clear, so you can seal the gaps without aesthetically unappealing white lines around the vent. It’s also waterproof, mold-resistant, and mildew-resistant.  

Gorilla Store Waterproof Caulk & Seal
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Are Return Air Ducts Required? 

Return air ducts are required to circulate air effectively throughout a building. You should have at least one return air duct per room, although larger rooms may need two or three ducts. 

Early HVAC systems had one return vent for the entire home, but professionals no longer consider this an effective or safe system. This is the reason you should have at least one return vent in every room of a building. 

If you have an old house, you might have one of the older systems with only one return air vent. If this is the case, you should keep all your doors open, so that air can flow throughout your home. You should also always check to make sure that the vent isn’t obstructed in any way. 

For more ideas, check out my article on how to increase airflow in ductwork. 

Read: How Do I Know If My Air Ducts Need To Be Cleaned?

How To Clean Return Air Ducts?

Keeping your return air ductwork clean is a great way to ensure that your HVAC system works as it should and helps promote good air quality. If you or someone in your family has severe allergies, keeping your ductwork clean is even more important. 

You can have a professional HVAC company clean your vents and ducts for you, but this isn’t necessary every time. You can do a relatively thorough cleaning yourself and save some money. 

Every month, you should also change your furnace filter. The filter gets dirty and clogged quickly, so replacing it regularly will help keep your air clean and high-quality. 

For more thorough cleaning, turn off the heat or air conditioning and use a vacuum cleaner with a dust attachment to eliminate any dust or debris. I also recommend using a microfiber duster to ensure you get the duct as clean as possible. 

My favorite microfiber duster is the OXO Good Grips Microfiber Hand Duster from This duster doesn’t require any cleaning chemicals to trap dust, and the large head covers a large amount of surface with every swipe. I also like its slim profile, so it can maneuver around tight spaces, such as pipes in an HVAC system. Finally, you can remove the microfiber from the handle to machine wash it. 

OXO Good Grips Microfiber Hand Duster
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I also recommend washing the vent covers at least twice a year. To do this, follow these steps: 

  1. Turn off the heat or air conditioning. 
  2. Remove the vent covers. 
  3. Place them in a sink or a bucket full of hot, soapy water. 
  4. Use a microfiber cloth to scrub the vents. 
  5. Remove the vents from the water and dry them completely. 
  6. Reattach the vent covers. 
  7. Turn on the heat and air conditioning again. 

If you’re looking for a good quality microfiber cloth, consider HOMEXCEL Microfiber Cleaning Cloths from The special grid pattern design helps trap more dirt and dust, and the material is lint-free and won’t cause any scratches in the paint of your vent cover. They are also machine-washable, so they’re easy to use repeatedly.  

Cleaning your return air duct doesn’t have to take too much time, money, or energy, and it can greatly increase your air quality and your HVAC system’s functionality. 

HOMEXCEL Microfiber Cleaning Cloths
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Supply vs. Return Ductwork

Return air ducts are just half of an HVAC system. The other half is just as important: the supply ducts. Knowing the difference between these ducts is essential to understanding your overall HVAC system. 

Supply air ducts blow conditioned air from the HVAC system into the rooms throughout the building. You’ll be able to tell which of your vents are supply vents because you can feel air coming from them. Some supply vents have adjustable slats, allowing you to adjust the airflow according to your preference. 

Read: Mold In Air Ducts Symptoms

Final Thoughts 

Return air ducts are an essential part of an HVAC system. These ducts pump air out of a room and send it back to the HVAC system, where it is filtered and reconditioned. This system allows the same air to be circulated throughout a building, which helps maintain a consistent temperature and promote air quality.