Q&A / 

Air Conditioning Blues – Return Air Problems

DEAR TIM: We just had central air conditioning installed in our two story house. The air conditioner seems to work fine, however the second floor rooms are warmer than the first floor rooms. It gets very hot upstairs in the late afternoon. What might be the problem? The contractor says this happens all the time. What, if anything, can be done to correct the problem? Where do we start? F. R.

DEAR F.R.: So, it happens all the time.... Maybe on his jobs it does, but not on mine. Your central air conditioner may have been installed by a contractor who doesn't realize that hot air rises and cool air falls.Successfully installed central air conditioning can easily cool two story houses.

Before we do anything else, let's make sure that the cold air from the air conditioner can get to each room. Check to make sure that the supply duct register in each room is fully open. Do not allow furniture to cover or block these air outlets. Check the ductwork piping in the basement or furnace room for damper controls on the individual supply pipes that go to each room. These controls are little levers that attach to a metal disk inside each pipe. They enable the contractor to balance or adjust the amount of air going to each room. Be sure these are fully open on the pipes leading to the second floor rooms.

For you to properly cool interior spaces, you must replace the hot air in each room with a sufficient amount of cool air. The amount of air required depends upon the size of the room, how many windows it might have, the number of exterior facing walls, the amount of ceiling and wall insulation, etc. The cool air enters each room through supply ducts. These can be located in the floor on outside walls beneath or very close to windows. In some instances, the ducts may be located in the ceiling.

Because hot air rises, it needs to be "vacuumed" off the ceilings in the second floor of your house. My heating contractor always accomplished this task by installing a return air ducting system which funneled the hot air from the rooms back to the furnace/air conditioner air handler.

Return ducts should be located in each room very near the ceiling on an interior wall. This return air opening pulls hot air from the top of the room. The heavier cold air which is flowing from the supply duct is pulled across the room and up towards the return duct. On its way to the return duct, the conditioned air cools you and the rest of the objects in the room. These same principles must be used to cool single story houses as well.

If your house does not have this return air ducting on the second floor, it frequently can be added. The challenge is to install adequately sized ductwork from the second floor hallway to the basement or furnace room. The hot air from the second floor rooms can be collected in the hallway and sent back to the air conditioner. Rectangular holes can be cut into the wall space just above each bedroom door. Each side of the hole can be covered with a standard return air grill. These holes allow the hot air from each bedroom to easily enter the hallway.

Once this hot air has a pathway into the central hallway, an experienced heating and air conditioning contractor can convert one or two stud wall cavities into the initial return air duct. At the floor level, this stud cavity is then connected to a traditional metal duct that is connected back to the return air ducting system. Sometimes this duct can be hidden in the corner of a first floor room or fitted into a first-floor closet.

Without this second floor return air system, the heavy cool air being discharged from the supply ducts in each room can't do its job. It often floats along in a layer near the floor. It eventually cascades down the stairwell to the first floor. This is one reason why your first floor is so much cooler than the second floor.

Author's Notes

December - 1998

I just received an email from Edna R. who lives in Oregon. Edna read this column and had an interesting story to share about another cause of poor circulation. I'll let Edna tell it in her own words.

"......We visited at a 3 year old rental home several years ago. The hosts were living in the kitchen and family room because the bedrooms at the far end from the furnace were too cold and the living room half way to the bedrooms was not warm enough to sit around in.

When I suggested they check out the furnace filter, they weren't even sure where it was. Apparently the previous renters didn't know either! The lint and dust were jammed into the allotted space and came rolling out in packed balls when the filter was removed.

Many people raised with electric heaters and fireplaces are often unaware there are filters on their forced air furnaces. They need to be told OFTEN to check filters and where they are in the heating system. Thanks for listening to me."

Column 143


12 Responses to Air Conditioning Blues – Return Air Problems

  1. I live in an old condo. My entire central ac needs replacement. My ducts are on the floor on the second floor. When the ac was working it was 15degrees hotter upstairs. I have gotten several estimates for a new ac. No one wants to run flexible ductwork upstairs without charging me a small fortune. Can I replace my entire unit (air handler, condensor etc and be ok with the vents for the ac remaining on the floor? I thought myself after much reading that it is possible to just get a whole new unit using existing ducts that I should at place a vent above each bedroom door. I was also going to use the opening where the whole house fan is located on the second floor for my intake. Will this work? Air conditioning is not my expertise, since I am a nurse not a technician. I also do not want to be taken advantage of by contractors. Any advice you can give me is welcome. Thank you. P.S Will getting ceiling fans in the other two bedrooms I have help? I have a ceiling fan in my bedroom

  2. Where would the return air for the air conditioning system go in a single family dwelling? The master bedroom, hallway or one of the other bedrooms or restroom which one?

  3. I have a two story home with forced air and ac, I have two hot air returns on each floor. The first floor is always cooler 5-8 degrees, which I have partially solved by shutting the dampers to the first floor vents in the basement to route more air upstairs. Would it be an issue to close one or both hot air returns on the first floor to pull more air out of the second floor?

    • You need to do what I told others to do. Go to the TOP of this page and on the right is my Search Engine. Type: air conditioning into it. Read every column that comes back in the search results. Your answer and MORE is there. You do what I say and you'll be COOL as a cucumber all the time.

  4. My family lives in the middle of a set of row houses, and we just recently replaced our AC unit. We are still having this same issue described in your post, and I am pretty sure this is the cause, since we do not have any return air ducts in our three story home.

    I have also heard of attic fans being a way of dealing with this issue. Do you know much about this method? If so, is this a more budget friendly alternative?

  5. We are doing some reconstruction on our home which includes brand new AC (condenser and furnace / air-handler) and duct work. Our home is a single-story 1780ft2 and located in Burbank, CA. The system was designed with a single large return vent in the hallway ceiling which is rather central to the house. There are air registers in all bedrooms, bathrooms, livingroom and diningroom/kitchen. However, the city inspector asked for another return vent to be added. The AC contractor insists that the current design is adequate but I'm inclined to give-in to the inspector rather than fight a battle which cause me the war.
    I was thinking of adding another return vent on the wall close to floor level near the location where the ceiling return vent is. The idea behind that is that the lower return would syphon off the cold air during winter time when the heat is running. The high return would syphon the hot air during the cooling cycle. I don't think the lower return would interference with the cooling cycle since there are no registers in the hallway. Air would have to make its way to the hallway from the far corners of the house where the registers are located. By that time cool air would have done it's job and gained some heat along the way, thus, rising to the top return. And I don't believe the high return would interfere with the heating cycle for the same reason.
    Ideally, I would prefer to install return vents with louvers to allow the closure of either top or bottom depending on the season. Unfortunately, I couldn't find any such filtered return vents. Please advise.

    • I was wondering if you ended up installing another return vent. I am having a similar issue. My builder built my house with one very large vent upstairs but some of the other homes in my area have 2 return vents. I'm not sure if I should continue fighting to have another installed.

  6. I live in a 4 level back split. There are cold air returns in every upstairs bedroom but they are on the floor across from the supply vents and that is the same on the main floor. Should I close these to prevent them from sucking my heavy cold air back to the furnace?

  7. Ok, I have a two story home in Buckeye, AZ, the house is about 3600 square feet with two A/C/furnace units located in the attic. The problem I have is that even know the upstairs and downstairs is cooled, there is one room upstairs that is always hot. Cool air goes in because I can feel it coming in through the vent and even know the other 3 rooms, the loft and even the bathrooms stays cooled, this specific room does not. An A/C tech came and said that I will need to have a return installed in that specific room. All the rooms have the same amount of vents, and there are two returns upstairs, one in each side, plus one of them is right by this room door. I have no returns downstairs. The entire house gets cooled pretty nice, except for that room. Will installing a return in that room solve the problem?

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