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Question DetailsAsked on 5/31/2014

My basement is freezing and my 3rd floor is hot!

My basement was refinished last year. Including a new central air system. The basement walls were insulated between the foundation and drywall. I had insulation blown in the attic in 2011. I have an operating attic fan.
When the ac or heat is set to 71, the basement temp is 52 and my bedroom on the 3rd floor is 75. Another bedroom upstairs is even warmer.
We had to purchase an electric fireplace heater for the basement this winter. The space is beautiful but it is too cold to enjoy! I don't think I should have a heater running in the basement and the air conditioning running upstairs!
I have dumped thousands of dollars into trying to remedy this and seem to be getting no where!!

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2 Answers


You did not say if the heat is hot air and if that was also installed last year with the central air. I would think you have contacted him as to the problems you are having if not that would be the best place to start. On a three installation I am surprised they did not spit it into two units. It may be just a question of having the system balanced, there should at least be adjustable dampers in the system that could be adjusted to correct setting. You may have to have them return for each season and mark ac and heat on the spot they should be. If you have two trunk lines you might be able to install motorized dampers controlled with thermostats, at least two one for the basement and one for the other floors.

If you have no return air ducts to each room that could also be a problem especially with bedrooms where the doors are quite often closed. If you have the door cut too close to the floor no air wiil return to the unit. You can have the door cut to at least an inch off the floor or if there is a hall you could cut in a register to each side of the wall so return air can flow through.

If the original installer can not help you should call a few HVAC contractors and tell them your problem and ask if they can balance your system.


Answered 5 years ago by ContractorDon


As Don said, this is not uncommon in single-path multi-story houses, and especially with basements because of their commonly dramatically lower ambient temperature. Solution is individual controls on the basement and the upstairs, or possibly the basement/first floor and then separate for the top floor.

It is possible that just adjusting dampers/vents could reduce this issue a lot - by cutting down the airflow to the basement. However, that risks increasing humidity down there with the reduced ventilation, which is not a good thing.

As Don said, the best solution is zoned supply to each floor, with individually controlled heat and A/C to each. Depending on your system, doing that may or may not be fully feasible, but with electric dampers and individual area thermostats you should be able to accomplish a lot, possibly with or maybe not needing a second run of duct for one floor.

A proper HVAC system design by an experienced, certified HVAC contractor, using the full design manuals to determine duct size, register opening areas, and return air needs for each area is your first step - those will tell what your system should look like, and then modifications can be made as needed to your existing system to solve the issue - commonly for the $1000 range unless substantial additioonal zoned ducting is needed.

One other solution, which is not legal in some code areas and requires automatic fire dampers between floors where it is allowed, is to change the return air duct (assuming forced air here) from a direct return to the central unit, and instead have it vent several places in the basement, with the central air unit then pulling the air from the basement. That would greatly increase ventiltion down there, and put the hot air in the basement in the summer, and warm air in the winter. It would have to be designed to prevent short-circuiting of the central air system in the basement, but can be done.

Can also be done with a scavenger fan taking hot upstairs air and moving it to the basement in a separate duct, independent of the HVAC system, controlled by a pair of thermostats that also have an off switch so it only runs when the upstairs is too hot AND the basement is below your desired temperature, and can be manually turned off if desired in winter to avoid stealing the warm air from the top story. This is called a Cape Cod Bypass by some of the old guys in the trade - commonly done in old high peaked two and three story houses to move the overheated top story or attic air to the ground-cooled basement without using any fuel (other than the electricity to run the fan). Again, not legal in all areas, and requires fire dampers in the ducting so the duct cannot become a flue in the event of a basement or downstairs fire, and in most areas has to be metal ducting.

Answered 5 years ago by LCD

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