Heat Pump vs. Air Handler sizing

12 years ago

I've gotten several estimates for a new heat pump.The most recent company is Angile's List A rated, Carrier Factory Authorized, and claim all their techs are NATE certified. Compared to other companies, the rep did a much more thorough job of measuring the duct sizes, including the returns, measured the square footage of the house, and used a computer program to calculate sizes. (The others used a paper slide-rule sort of thing)

But he's recommending a variable speed 3 ton to 5 ton air handler(Carrier FE4ANB006T00) to go with a 3 ton Greenspeed heat pump. I'm concerned about such a large mismatch in capacity. I asked him about humidity control, and he said the larger coil in the 5 ton air handler would improve dehumidification. But if the lowest airflow it can supply is 3 ton, vs. a smaller unit varying from 2 to 3.5 ton.... I just don't know. He also says this combination of 3 ton compressor and this air handler has the highest SEER and HSPF ratings.

Does anyone have any expertise and thoughts on whether this is a good match or not? The house is about 3800 sq. ft, and the ducting (he says) supports about 1420 CFM on the supply side and 1250 on the return, but he's also going to enlarge a too small return duct in the basement.

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Comments (3)

bsmith
12 years ago
I personally would ask him how many of these variable speed units specifically has he installed, because it sounds as though he doesn't fully understand or appreciate them.

Forget about the fact that generally oversizing the air handler above 1/2 ton (especially without mention of an expansion valve) might mean potential future compressor failure. Better yet, I personally would get a quote from another dealer.

If you are worried about dehumidification, get a whole house dehumidifier. Although my aunt in Florida has a 3-ton Greenspeed and has found no need for dehumidification with these variable speed units.
mike_home
12 years ago
The contractor wants to install a 3 ton condenser to cool a 3800 sq. ft. house? I am skeptical about the sizes. What is your location? What area of the house does the 3800 sq. ft. include?

It is common to install a coil larger than the condenser as long as it as valid AHRI match. Ask the contractor to provide all model numbers and the corresponding AHRI certificate number. This will confirm whether is a valid equipment match.

There is a debate among HVAC pros whether a bigger coil improves humidity removal or not. I have over sized coils with my Carrier Infinity AC condensers and I found it works very well.
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sktn77a
12 years ago
I wouldn't worry too much about the condenser/coill size difference. Just make sure he did a "Manual J" estimation of heating and cooling needs (as opposed to a Billy Bob's freebie HVAC calculator spreadsheet that divides sq ft by 600 and then adds a ton)! Unless you are in a very mild climate and/or have a super well insulated home, 3 tons may be a little skimpy.