currently using a Goodman 24000 BTU Central air, installed in '96. it is starting to cost too much because of leakage of refrigerant. I did the size calculator thing and it recommends a 30000 BTU unit, but that size just doesn't seem right (24000 all day sometimes to cool down from the mid to upper 80's °F to 78 °F). I think that it's too small, and think it should be larger. I am looking at a 36000 BTU system, but someone else said that is too high for the square footage.

My main floor is 1100 SF and the basement is too, (2200 SF). I cool both and calculated that in, that's why I think 36000.

1 calculator says use a 2.5 ton, but if you use the oven a lot, to bump it up 1/2 ton more. My wife and I both cook a lot.

What do you think?

In 96 it still took 4 or more hours to drop the temp 6 degrees. Its been recharged 2 times since it was installed, 1 capacitor replacement. The last recharge cost $225, 2 years ago. The furnace however has had 4 controller boards, 3 temp sensors, and 2 blower motors. That is why I am looking for a replacement for both. The furnace size is not an issue, only the question about the AC size. I just don't want to get an AC too big and cool the house, before it removes the humidity and then have that issue to deal with, although I could run a dehumidifier if it's too big an air conditioner. My house has 2 big trees, for now, one on the East and one on the West, but the one on the West will need to be removed in the next 2 years. That is why I think I'll need the 3 ton, vs the 2.5 ton. The West side has a big sliding glass door, but all the windows are double glazed and low E glass.

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How did the system perform back in '96 or at least on a good charge? Ideally someone preformed all the necessary 'manuals' and it was the correct size to use. I lived in a 1700 sf apartment that was always a little hot until we switched out a 2.5 for 3. It all depends on your heat gain: windows, drafts, insulation, lighting, appliances, humans.... If you are not going to pay an arm and a leg for a professional calculation, I would charge it up one last time and see how it preforms on a nice hot day and then decide if its undersized or just neglected. Charging it back up would cost less than a full load calculation I would think. Or just go with a 3 ton. Although the problems can be just as bad with an over-sized unit, they are much less prone to present themselves then in an under-sized unit. It may cost more to operate but it will work as opposed to it almost works.

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