If you put my arm around my back and forced me to respond I would probably be lead to say 'AC system may be over sized'.

But you really didn't provide enough information.

What are you trying to do?

The other thing is this: if you are too cold, shut the AC system off.

It's either that or you tell the world what you are trying to accomplish. Also tell us your location... we know you have a basement but it's still not enough information.

Thanks for responding. I'm happy to answer any questions. AC is 3ton, and might be slightly oversized by about half a ton. 1st and 2nd floors are reasonable temperatures. It's just the basement that gets really cold in the summer. Thermostat is on 1st floor. Ductwork in the basement is not insulate and probably a bit leaky.

I'm just trying to efficiently get the whole house including the basement to stay around 70 degrees in the summer. Basement is fine in the winter. Location is Pittsburgh, PA area. Any other questions? :)

Thanks

Google heating or air conditioning zone dampers.

If you set the thermostat to 70 degrees for the upper floors then the basement will be colder. My suggestion is to insulate the duct work in the basement and seal the basement vents so they don't leak.

What is the humidity level on the upper floors? Do you not feel comfortable at at a higher temperature?

Your goal of 70 degrees for all areas is not realistic due to the design of your HVAC system and architectural design of the home.

The thermostat on first level is torn between 'attempting' to keeping the 2nd floor bearable without making the basement too cold.

Problem is cool air falls and hot air rises. So trying to keep the 2nd floor bearable without making basement too chilly is a recipe for disappointment.

The best way to accomplish what you want is called a HVAC ducted zone system. However, this solution may not be practical and if not done properly could create other problems. Often times people are shocked what it takes to rectify problems of this nature. Certainly there are those out there who will sell you anything, then slam in in any old way. This method of slam jam may work 20% of the time, until temperature extremes come. Remember it's not just about getting this to work when it's warm out, it's also about getting it to work when it's very hot out as well as when it's really cold.

With that said, to do this you would need 3 zones minimum. 1 for basement, 1 for first level, 1 for 2nd floor.

Each zone would have it's own thermostat with control of the equipment. By doing it this way you probably wouldn't have to keep first floor as cool as 70 degrees, which would reduce the amount of cool air to the basement due to the cool air falls principle.

If the basement is open to the 1st floor, there can be spillover to the basement especially when operating in cooling mode. The basement is naturally cooler and so without heating it / it's possible the temp down there will be less than the desired 70 degrees.

The other design flaw you may be up against is return air problems. If the 2nd floor doesn't have a dedicated return to the equipment this can trap heat on that floor which can cause operational problems or hurdles for the system to over come. It would be best design wise if each level has a dedicated return in which a zone system is implemented. But realize there is much more than this to properly design a HVAC zone system.

Can you temporarily block the basement ducts? If you can do that, and the basement becomes comfortable (both in terms of temperature and humidity), then making this permanent might be a solution.

As other people have recommended, if your basement vents don't close and seal adequately you should block them with strong magnetic vent covers or rubber vent covers. If you're going the magnetic route get strong magnetic vent covers because the ones with weak magnets will fall off the basement ceiling vents. Also, there is a new product called the Ecoflap auto vent cover which you can use on the upstairs floor vents which also helps keep AC air upstairs. It works by automatically closing the floor vent its covering when the AC shuts off and when it closes it prevents the AC air from backflowing into the floor vent and flowing down into the basement which is where it goes because cool AC air is heavier than ambient air. Also keep your basement door closed and if possible put a auto door return on it to automatically close the basement door. Also keep all bedroom doors and other upstairs doors closed if possible which will also help keep the AC air upstairs. Plastic seal strips on the door bottoms will also help.

Thank you for the suggestions, but I no longer live in that house. Lol

Thanks for responding back Ben... the suspense was killing me.

True HVAC solution versus spending 'real' money. If I've seen it once I've seen it a thousand times. (Sell it to someone else.)

I've titled this song: 'How Am I Supposed To Sweat Without You?'

I could hardly believe it when I heard the news today, but I can see by the look on your face to know it's true.....