Questionable Size of Condensing Unit

[Rick Hurst]

2.5 ton Carrier Puron High Efficiency Unit

Living area is 1740 sq.ft.

Unit is on east side of structure.

West side has 3 windows, south side 4.

NO trees or shade.

8ft. ceilings throughout.

TD was only 15 degrees. Filter and coils were clean. Refrig. line was cold.

I suspect that this unit is undersized for the amount of square footage present. Here in N. Texas we see 1 ton for every 5-600 sq. ft.

I've been on the phone with several HVAC companies and they say it is on the low side on size but should be adequate.

The condensing unit ran for the 4 hrs. I was at this home without shutting down.

Any opinions.

Rick

[Ted Menelly]

I have run into this size unit for the same size home also. No matter what I figure with total openings, type of windows, insulation etc., my figures keep coming out to the unit is to small. HVAC techs I have talk to say that for the basic cubic feet of space to be conditioned it is properly sized to handle the home. I keep figuring 3 ton. With the unit being just the minimum size for the home it will run longer and you talk a higher efficiency unit and take a good part of that efficiency away.

[Jim Luttrall]

Hey Rick, take into account the humidity, outdoor ambient and indoor air temp when you arrived. If the air was off or indoor conditions were substantially warmer and wetter than normal, then the unit will tend to run longer to satisfy the latent heat load of humidity. Also, if this was in the last day or two with the tropical storm force winds we have been having, you will loose a good bit more of conditioned air than normal due to air leakage. Sounds like the unit may be on the small side, but running for 4 hours without shutting down during the heat of the day at design temperatures is actually the preferred method of sizing. Unless you have a variable speed unit, too large a unit will not reduce the humidity properly and will leave the air "clammy" and a unit the cycles on and off repeatedly will use more energy than a smaller unit that stays running.

Bottom line, I can't answer your specific question on sizing but I would not jump to condemn the unit as too small without more information.
Jim

[Nolan Kienitz]

Rick,

Ductwork installation (quality - or lack thereof) will also play into all mentioned. That is one of the key elements I see that can severely impact the performance.

The South & West facing windows are certainly going to make it work one heckuva lot harder without shade or solar screens. They could be added and that too would help.

I checked with my HVAC contact and he felt it "could" be on the margin of being small, but there are so many other elements as you noted.

[Rick Hurst]

Nolan,

4 out of 5 HVAC contractors I called said they thought it was going to be undersized.

The other 1 said it will probably be ok, if they would spray the attic with a radiant barrier.

Go figure.

rick