About Cold Air Return Vents

November 30, 2008


About this time every year, my blog gets a lot of traffic from people searching for “can I cover my cold air return vents?”

Answer: no.

I want to address this issue again. If you have a forced air furnace, realize that there is an exchange of air going on with it– cold air to hot air. Your furnace needs to take in cold air, heat it up, and blow it out through your heater vents as heated air. If you cover your cold air return vents, you are starving your furnace, creating an air vacuum in your home (leading to an uncomfortable atmosphere), and perhaps filling your home with trace amounts of carbon monoxide.

Do not cover your cold air return vents.

I did a post about this when I renovated my living room, and re-did some of the furnace ducting to the room. I had done some studying and talked with my furnace guy. You can read the post here.


Now, my home has cold air return vents, but not enough. Not only do you need vents, you need a proper amount for proper air exchange. My house, at about 1680 square feet, only has two small cold air return vents– for the entire house! That is far too few. My Furnace Guy said that for every heater vent (and size) in a room, there should be a cold air return vent. Bedrooms almost never have them, and this explains why bedrooms are so cold in the winter– there is no full air exchange but rather a vacuum of air. The heated air really has nowhere to go, since there is no air flow; and the room air remains stagnant and chilly. So ideally, every room should have a cold air return vent (or at least larger ones in key areas of the home). I know, I know! Replacing and rebuilding your home’s ducting system is not as easy as replacing all the kitchen sinks! With ductwork, you have to rip out walls and work with metal. It’s NOT fun. However, the next time you have a wall open or if you decide to build an addition to your home, keep these things in mind. Your furnace will appreciate it, and it will show in the heating bills.

And in the meantime, keep those cold air return vents uncovered!

Photos courtesy of Americanhvacparts and Office of Energy Efficiency of Canada.

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12 Responses to “About Cold Air Return Vents”

  1. Wendy Says:

    We’ve been living in the high desert for 3 years, coping with a “swamp breeze” pretend A/C that was built into this house when this area obviously had a much cooler climate. At any rate, the one positive to this is that during the winter, all those cooler vents become heater intake vents. So our heat is coming up through the floor, and being taken back up at the ceiling, in every room. It is very efficient & we’re able to keep this old, drafty-like-a-sieve house pretty warm in winter. The intake vents are as important as the output to keep warm air circulating.

  2. Barry McPhee Says:

    In my old Vermont house, with an oil furnace, I’ve got two vents clearly, forcefully, blowing cold air out into the house. Because of this, it seems impossible that they are cold air *return* vents. How can I confirm that they aren’t? Second question: can the furnace itself have the only cold air return vent?

    • Mrs. Mecomber Says:

      Hi Barry. Well, I’m not a furnace expert, but what I’d do if it was me is this:

      1.) Make sure your ducting system is set up right. If you look at your furnace (you’ll see all sorts of ducts leading everywhere), you’ll see an “in” large duct and an “out” large duct, with many smaller ducts branching off of those. That’s for most forced-air furnaces, anyway. Check and make sure you know where the ducting system branches off into, and become familiar with your furnace system.
      2.) My hot air return vents ALWAYS blow out cold air for the final three or four minutes right before the furnace stops. This is because the furnace fan keeps spinning for a little while after the gas heating flames go out– this is natural, to ensure that all the hot air has fully pushed through into the room. It’s the normal part of the cycle.
      3.) Maybe your hot air vents blow out cold air because they are either too far from the furnace (like a third floor) or you don’t have enough cold air return vents and the furnace is just blowing whatever air it can find (and in an old home in a Vermont winter, that would be cold air).

      I hope those tips help.

  3. Chip Donovan Says:

    Question, I just heard a humimng sound in my heater and it appears to be on the intake side. Any thoughts

  4. jessi gerl Says:

    Our home was built in 1908. The exterior is sandstone and all the inside walls are plaster. The windows are all very old and some do not even close all the way. We have 1800 square feet between the upper (attic, which was built into a huge bedroom) and the main floor. We recently closed off a doorway which connected the two downstairs bedrooms through a hallway and a bathroom in between the hallway. The cold air return is in the floor in this hallway. , It is huge and takes up most of the hallway. Is there anyway I could move the return into the wall in the hallway, or in the floor of the master bedroom? We wanted to convert the bathroom and the hallway to a master bath using the floor space the vent takes up. Besides this vent is uncomfortable to walk on and always has a musty smell. Please help. The Gerls

    • Mrs. Mecomber Says:

      Jessi– as long as you have cold air returns, that’s better than nothing. I am no furnace expert– you can always call your local Heating Repair Company– but I have learned that cold air returns are best placed on the exterior walls of the house. But if this is impossible to place, then cold air returns anywhere are better than no cold air returns at all.

      Yes, we have a few musty-smelling vents/ducts, too. One of ours is wooden!! I am working on replacing them entirely. If your ducts are metal, you can clean them. I hired my heating company to clean them, but they did not do a great job; it turned out better when I dismantled the ducting myself (I had to take it down anyway) and washed them.

      All the best!

  5. Shari Says:

    Hi I need help with either toning down the noise of my furnace or installing a device on my television that adjusts to the sound in the room. I live in a poorly designed condo where the furnace is in the center of the unit along with all of the vents which run along the ceiling. The cold air return is of course in the living room and seems to magnify the noise of the running furnace. The return opens into a 2′ x 4′ metal box before going to the furnace. Is there someway to reduce the sound or is my best bet the television devise?


  6. Pat Says:

    I need help! When the wind blows, cold air blows out of my cold air return vents when the heat is off. How do I stop cold air from coming out of these vents?

    • Mrs. Mecomber Says:

      Pat– not sure. If it was me, I’d look for ducts that have become unsealed (or ducts that were never sealed, as ours were not), or a drafty basement or an unsealed return shaft on your furnace. Mastic tape will seal metal ducts.

      Just so you know, after the heating cycle ends and the burner in the furnace shuts off, your furnace continues to blow air through the ducts for a period of time. This air may feel cold, because the furnace burner is not on anymore. The reason for this is so that the furnace blows out all the remaining dregs of warmed air from the heating cycle. All forced-air furnaces do this, to my knowledge.

  7. Tim Smith Says:

    Not all forced air systems keep the fan going after shutoff and some do longer than others. ALL energy efficient models do however so just about everything made in the last 10 years will do this. Its the system making use of the heated element after the burner is shut off (or electricity is cut off depending on the system). Many people complain their old system did not feel cold and the replacement does, this is why.

    Returns are VERY important but there are work arounds. If you have a few rooms that get cold and you open the vents up and they remain cold compare to the rest of the house try leaving the door open. If that helps one might think its because the heat from the house can get into the room but whats really happening is the room does not have sufficient returns. When the door is closed even though the heat vent is wide open the air has no where to go causing pressure. You may even here the door make a noise when the air comes on as the pressure hits the room. Because of this pressure the furnace cannot blow as much air into the room. When you leave the door open it can.

    You can test this buy placing a hand near the vent with the door closed and the air on and have someone close the door, if you feel less air coming out you do not have enough return venting. The poor mans fix is to leave the door open. The more expensive fix is duct work to add more return.

    The farther away from the system the more this becomes a problem because most systems have a main air intake at the unit itself. Even through the filter the system finds it easier to suck in air at the unit then through its returns if the return lines are lengthy.

    Its a science to be sure. One solution is to go ahead and open up vents in the basement and let the heat travel upstairs on its own eliminating back pressure to the rooms. Experiment, as another person said, its always good to know your own system.

    Another tip is to get a programmable thermostat that tries to keep temp to less than a degree variance. Your system will come on a lot more but that makes it more efficient as it makes use of geothermal energy storage and heat trapped in your furnace (not letting it ever really cool down) which in turn also extends the life of the main heating element.

    Another possibility is to create passive returns to relieve pressure in the rooms. These are returns not connected to the furnace. These are usually installed to “equalize” pressure. Their downside is just noise, so if thats not a problem its the way to go and VERY easy to do. When some people see them they may seem like they have no purpose but they can take a cold room and fix it instantly. Here is what you do…

    If you have a cold room that does not have enough return you find a interior wall and cut a hole in the drywall slightly smaller than a simple register grate, do the same thing on the other side making a simple “hole in the wall” between the cold room and a main area of the house, place a simple register grate on each side (does not need to be adjustable). Do this for all the rooms that are cold with the door shut. Now when the air comes on the displaced air in the room has somewhere to go. This “equalizing” of air can fix most return problems without fancy duct work but has the downside of noise which for most is not a problem (unless its a teenagers room!).

    With a completely equalized system now you just adjust the vents according to desired temps. If adjusting the vents does not seem to make any difference you have a return/equalize pressure problem.

    Note: DO NOT assume that adding more incoming vents to the room will help, if its a return/equalize problem that wont do anything.

    Hope this helps and if you have a radiant heat system (boiler etc) this does not apply.

  8. Felicia Says:

    I live in a very small home that is about 1,200 sq ft. There are return air vents in every room anand in the winter our bedrooms stay freezing cold and the vents are blowing out freezing cold air. We are all staying sick and it is getting old! I can’t afford to have anyone come look at it but I need to know if there is a simple solution I can do on my own to maybe help?


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