I'm in the process of replacing my 80k single stage heater upstairs with a 60k trane modulating unit. The heat load is 41k.
I'm considering taking advantage of soon to expire rebates, and replacing the AC. It is 3 tons, and 17 years old. It is on the second floor, 1500 sq ft. The load calc program I used (as recommended here) came back at 24k btu. However, when it is mid 90's outside, the temp upstairs rises to 81 or so. The old "oversized" unit can't keep up. Is it because the calc is bad, or the unit?
If i were to replace it, what size should I get?