HVAC setup question

Question about HVAC set up… Two story home, approximately 2000 ft.²… Two separate systems. One is 2 2 1/2 ton AC with a 60,000 BTU furnace. The other is a 2 ton AC with a 40,000 BTU furnace. But the bigger furnace is serving the top floor. That seems odd to me. Is that because the garage takes up some of the square footage of the main level?

Sizing of systems depends on where you are located. So where are you located? Also what is the square footage that each system is serving? Not total square footage.


In Atlanta. I’m pretty sure it just has to do with the bonus area above the garage. Just hasn’t caught my attention before since I don’t tend to have the furnaces on while inspecting them but today I did.

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More living area on upper floor and hot air rises, so more AC.


I agree with, David.

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I agree with Larry !


Help me understand why that wouldn’t hold in reverse, too, though…wouldn’t you want a bigger furnace on the main level since warm air rises and you won’t need as much heat on the second level as a result?

I would think in Atlanta cooling would be a much bigger issue than heat . Just the opposite here in northern Ohio…


Now, I agree with Jim!


Helpful thoughts! Thanks to all.

Sizing of each system is based on calculations performed by a mechanical engineer. Those calculations are typically based on location, design temperature (Atlanta’s climate), volume, space use, square footage, etc. (I’m sure there are other parameters I am missing).
A good mechanical engineer will factor lot orientation.

Mechanical Engineers don’t necessarily take into account the heat rising effect unless they need to condition large vaulted rooms, hence volume.

Things to also consider, is it a custom home or a “track Home”. When was the home built? Designs for a house built in the 1950’s will defer to a 2020 house. What code was the house constructed to.

REScheck will also take into account the other aspects of the buildings construction to size systems.


I am in Atlanta, Big system for top floor, medium for bottom and smallest for basement. We have two cold months out of the year, it is all about cooling.


It could be due to the size of the blower capacity. The 40,000 BTU furnace may only have a 2 ton blower. That is why they needed to increase the size of the furnace. Its possible that they derated the BTUs of the larger furnace to compensate.

I agree with Larry and Jim. :slightly_smiling_face:


So… now we are supposed to be doing heat loss calculations as part of an inspection? The furnace works or it doesn’t. The AC unit works or it doesn’t.

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You’ve got that right according to our SOP, James.


Good advice.
Note that the system(s) function or don’t and recommend an HVAC contractor preform a clean and check upon taking possession of the home.

A load calculation is needed to size heating and cooling systems properly.
That said, unless there is a significant amount of glass, 100,000 BTU seems way over sized.
4.5 Tons of cooling for this size house is definitely oversized.

Pretty sure the OP was just trying to learn something. I don’t think he was going as far as to say he comments on this in his reports.


You may be right if that is the case my apologies to the OP.