Two-story home to systems sizing mystery? at least to me

Doing an inspection on a new construction with Two electric heat pumps with gas pack units.
Because it is new construction I do not have a sketch to be able to determine exact square footage up verses down, however total square footage is 4,108 square feet and I am estimating that the main level is probably 500-600 ft.² larger than the upstairs (same footprint except added master suite at the main level) . (Ceilings are 10 feet high both levels)
The electric heat pump serving the main level is 5-ton and the upper level is 4-ton, which makes sense.

Now this is the issue or question I am having…
The upper level system’s gas pack, as we call them here, electric heat-pump with auxiliary being natural gas fired) is larger than the main level unit
Upper level unit is a 100,000 BTU input and 95,000 BTU output.

The main level auxiliary gas pack unit is Smaller 80,000 BTU input and 76,000 BTU output. The main level also does have 2 zones (thermostats) one for main portion of main level and the other for the master suite.

Now the other discrepancy I did find was the upper level heat pump system would not go into cooling mode but actually went into heating mode when indicating cooling and I lowered the thermostat temperature a few degrees. It actually kicked on the heat with gas pack running raising the temperature and I guess it would’ve just kept running until it hit 190°F (which is the maximum outlet air temperature of the unit… So that’s a big Write up… It would shut off after I raised the thermostat higher. than what the ambient temperature was. So they have something goofed up there.

I know it’s beyond the scope of a home inspection to size a heating and/or cooling system however I’m just wondering if a mixed up when they installed the systems???

I’m thinking I should make mention of this to have it double checked by the HVAC contractor to make sure that they didn’t mix up the units when they installed them.

Here in GA, the larger unit for cooling is upstairs. I am curious if the “heat-pack” has to be sized with the cooling side tonnage. I guess I did not answer your question, but rather adding to it.

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Reason says the larger heat unit should be downstairs as hot air rises.


HVAC should not be sized based on square footage alone. The only way to know is to have a proper heat loss calculation for first and 2nd level of the house. For example, if the second level has a lot more windows, it may need more heat capacity. If you’re going to call our capacities… you will have to call them out in every house because they are almost never sized correctly.


Zoned systems, no matter the flooring structure, is beyond my SOP. I note it and suggest further evaluation to determine proper efficiency based on system setup. Never had any push back from that.

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I’m not about to start trying to figure out sizing or doing heat calculations this 1 (new construction) I just really have a question because on the surface it looks wrong to me. Also our climate is warmer we are very much more like Las Vegas (about 8° cooler on average). It just does not make sense for this very much smaller area to have a heating system larger than the lower. I think I’m just going to report that the HVAC company should verify that they are correct and leave it at that is it does not look right to me. As busy as everybody is here I wouldn’t doubt if a very inexperienced helper may have installed these and that might explain why the cooling system/thermostat controls are messed up.

Now I did get the thinking which is kind of dangerous… It might be because of the 2 zone system on the lower unit that it would just be too much (heat output) if only one zone is being used. My heat-pump is all electric and mine won’t go into auxiliary heat unless I crank up the thermostat. It can get very cold here but very seldom do we get below 20°F. That’s the only thing I can think of is this because of the zones is why it is smaller. The electric service is very cheap here. I all electric heat-pump is less to run than someone that uses gas for heating here.

Ok first, depending on the design of the house you may need more heat on 2nd floor. You need to add up the SF of the walls, floors, and ceilings on the second floor that do not have a conditioned space on the opposite side. You may have a garage under some floors, the attic is not conditioned, and as someone said, windows.

Second, the lower floor has a zoned system. One of the advantages of a zoned system is that you can use smaller equipment as the two zones do not call at the same time or temp. An oversized unit costs more to run, and it over heats and cools when only one zone is calling. This can make things very uncomfortable, and will not extract latent heat properly causing moisture issues as well.

Need more house information…


Too many variables, size, insulation, fenestration, orientation etc. But looking at the general info you provided the system looks too big, imo.
Here is a website that I was using recently, try it.

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Thank You everyone for the input. I’ve decided to NOT call this out in the report, however I’m going to call my client and explain how it is beyond a home inspection to figure out sizing for equipment and even if it was, there are too many variables to consider and I just don’t have the information available to determine if there is a problem or not. I thought it best to verbally inform him of my concerns and have him ask the Builder/HVAC contractor to explain the reason for the larger heating unit for the smaller area. Could be a very good reason.

Since they did screw up on the control of this system (Heating when set in cool at thermostat) And didn’t bother performing an operations check after install (how can anyone not RUN a system and check to see if it is operating correctly before walking away??) I don’t think it is out of bounds for me to Question if they know what the hell they are doing (in a diplomat way).

Now it just could be that the HVAC contractor knew beforehand just how bad the Insulation contractor was going to insulate the attic…and is trying to compensate…(Actually used the words “Was Installed in an Unprofessional like manner” when I called out the crap insulation job (ceiling drywall showing).

  • They also did not put the PVC rain cap on the Direct vents at the roof. Combustion air (and rain) dumps directly into (both) the unit’s housings.

One round up narrative could help.

Due to numerous issues such as a,b, and c. Recommend a complete technical evaluation of the entire system by a qualified HVAC contractor.

I would make sure my narrative was written in such a way that a follow-up phone call is not needed.


I like that, Thanks Brian, Have a great weekend!

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Thanks, you as well kind sir.