Conflicting Info on HVAC Size

10 years ago

First time poster hoping to get opinions. I have a 1500sq house built in 1978, all electric, forever home. I currently have a 2 ton Trane that is original to the house. After several estimates where they measured room size, windows, ceiling height and such, the way I understand it, my calculations come in somewhere between a 2.5 & 3 ton unit, but closer to 2.5 than 3. A couple of the contractors say I need a 2.5 ton and if I go bigger, the unit could cycle on/off too much and cause problems. Most are saying I should size up instead of down in Texas heat where AC is used 8-9 months per year. I am planning to get another Trane (not that I expect it to last 35 years too.) The 2 estimates I was leaning toward are both 3 ton. Company 1 proposed heat pump condenser model # 4TWR5 (XR15) with fan coil model # TAM4 (XR15) with 10yr parts, 5 yr labor warranty, and company 2 proposed 4twr3036c1000a (XR15) heat pump with gam5b0b36m31sa fan coil with 10 yr parts, but only 1 yr labor and 1st year free maintenance. Cost estimate for both is right at 6k. Both include replacing line set, touch screen thermostat and other misc items that appear to be equal. Company 2 included upgrade to variable speed tam7a036h31sc for $578.00. Company 1 did not include in their estimate but upgrade cost would probably be close. All the contractors have said the attic insulation and ducting is adequate, until my last estimate last night. A young little fellow said I only have 1000 CFM's of ductwork, not enough for a 3 ton unit. I won't use the young fellow. Among other things that happened, he did not remember to put my air filter back in. I'm not sure I trust his measurements, but it does concern me that no one else mentioned anything about CFM's that I recall. Now I'm 2nd guessing myself on everything. Maybe I need 2.5 & not 3? Is there anything else I need to consider to determine the correct size? Of the model #'s suggested, is one combination better than the other? Is it worth $578 to upgrade to the variable speed? Any other input is appreciated. Thanks in advance.

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Comments (4)

jackfre
10 years ago
"All the contractors say the ducting is adequate" Did they test it? If the acting is in fact tight I'd think the 2-2.5 ton would be best. Google www.DOEductleakage.com and read for a while. I think I would recommend a pressure test on the system first and make decisions testing and repairs.
TXTerri
Original Author
10 years ago
Thanks, I'll read it. Who would do the pressure test, the AC company providing the estimate? If it makes a difference, they are calling the ductwork fur down. I asked company 1 about the ducts. Here is his response. Does this make sense? "With a chase designed duct system you need more air flow so that the vents at the end of the chase get the same as the ones closer to the unit. This is why I went with a 3 ton system. If you go with a 2.5 ton unit the duct runs further away will suffer in volume." Thanks
mike_home
10 years ago
Did your 35 year old 2 ton AC keep the house cool in the summer? If it did then that is a strong indicator that 2 tons is sufficient.

I am skeptical that your house was built with a 2 ton condenser and duct work which can handle 1200 CFM of air flow. If you going to increase the size then I recommend no more than 2.5 tons. The duct work should be fixed if has leaks.
sktn77a
10 years ago
Living in Texas, humidity is as big a concern as heat. Oversizing a single stage unit will cool the house down but it will be cold and clammy - not very comfortable. Get a correctly sized system with a variable speed air handle that has a humidity controlling thermostat (this could be 2.0 or 2.5 ton). Unless your house is poory insulated or has lost of south facing windows, a properly functioning 2 ton system sounds about right. I'd be surprized if the ductwork for your previous 2 ton heat pump system could only handle 1000CFM but get this double checked.