Pretty much the title. I have a full basement. Part of it is unfinished and has the water heater, furnace, and washer / dryer. The other part (roughly 1/2 of the total space) is partially finished. It has a dropped ceiling and wood panel walls, both with no added insulation. There is an AC / heat vent cut into the ceiling. It is currently taped shut. There is no cold air return.

Even with the vent closed, that area of the basement stays pretty cool even in the hottest part of the summer. I'm assuming because cold air sinks and the ceiling isn't insulated. I'm thinking about adding a cold air return near the bottom of the floor and uncovering the vent. The thought is that the AC would cycle air through the basement and pull the cool air back into the main living area. Should this work? Anyone have before and after experience doing this kind of thing?

  • Most whole-house air conditioners work by grabbing air, conditioning it, and pushing it through the furnace vents up through the house. Where is it grabbing the air from? When the system pushes conditioned air into the rooms, the same amount of air must leave those rooms. Where does it go? Jun 8, 2018 at 21:57
  • pull cool air from basement floor and blow it upstairs
    – jsotola
    Jun 8, 2018 at 23:25
  • Please clarify terms. In the summer it would be a warm air return?
    – paparazzo
    Jun 8, 2018 at 23:44
  • fwiw, I've seen a huge grid return right on the side of the unit in the basement...
    – dandavis
    Jun 10, 2018 at 6:27
  • 1
    Before you do this, I’d see if you are in a radon gas area and if so, you may want to do a radon gas test. They’re inexpensive and worth the piece of mind. Your precious home’s owner may have blocked the admixture of basement air with the main home air based on the fear or tested reality of radon gas.
    – RoboKaren
    Sep 11, 2018 at 3:46

4 Answers 4


Furnace installers and/or home owners will put a registers in the duct work to provide some heat or A/C to that area. The number of these supply and return registers is determined by the typical use and desired temperature of this area. I recommend that all basements should have at least 2 supply registers and 1 return register in the basement/equipment area just to keep that area slightly warm or cool and the air fresh. If you are going to finish that area to be used as living space, then more supply and returns will be needed. Also you may want to close the supply registers in the summer when using the A/C since cold air is heavy and will move to the lowest level in the house. Leave the returns (mounted at the floor level) open to circulate that air all the time.

  • Thanks. I think I will add a return. I'm not sure if I will add another vent. I'm not interested too much in climate control. Really just trying to recoup the cold air. If I added a return and kept the vent closed would there be enough flow through the return? I figured I would need to open the vent so there would be air entering the room instead of trying to pull a vacuum, or pull hot air from the unfinished area. Jun 9, 2018 at 0:15
  • I have a finished basement in my house. I have 6 supply registers mounted in the ceiling and blowing down and 5 return registers mounted at the floor level. If your basement is mostly unfinished, I would have at least 2 supply and 2 returns just to move the stale air that will accumulate in that space. In the winter I would open the supply registers and in the summer I would close the supply registers, The returns will only move as much air as is present with very little negative pressure in the basement, since all the house returns are tied into the same system duct work.
    – d.george
    Jun 9, 2018 at 10:36

We must assume that whoever taped the supply vent shut did so for a reason--probably it was too cold in the summer (and maybe or maybe not too hot in winter). Too much conditioned air was going into the basement space and not enough into the upper floors.

If you put a return into the basement and open the taped up vent, then even more conditioned air will go into the basement--the opposite of what you want. First try leaving the basement as is and opening up dampers or restrictor vanes in the supply vents to the upper floors to allow more flow into the upper floors.

Does your system have a return vent system? If so, if you later want to provide airflow to the basement you could install a return vent and connect it to the return system. But if this would be difficult it might be sufficient to simply have a return air connection from the basement to the floor above. Of course, this might reduce audio privacy depending on how it was done.


I have installed air intakes in basements many times. The natural cooling will reduce your AC bill. If your stairwell to the basement is open you don't even need registers down there and the furnace will push the cool air through the duct work. By installing dampers you can change the flow from different levels by season. My last home I did exactly that and it greatly reduced my cooling bill and I had a wood stove down stairs that shifting the dampers for winter saved me a huge amount on heating and all I did was change the volume of air removed from upstairs or downstairs. Upstairs open fully in the winter downstairs in the summer. It worked great and saved quite a bit while keeping both zones more comfortable.


Get one of the AC units that have wheels and sits on the floor and exhausts out the window and use that at on the top level. Your Central AC wont work as hard. I have just done this and my electric costs have actually gone down.

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