PLEASE HELP....HOW ACCURATE IS HVAC-CALC
Here is our quandary. We have been taking a crash course in HVAC as it seems that the contractors in our area go with "if the house cooled with what you had in the past, then that is what you should go with." We had one contractor (who we are going with who did measure - NOBODY ELSE WOULD DO IT>>>SAID IT WAS A WASTE OF TIME IN AN OLDER HOME).
This is a 1 ½ story house that is going to be ONE Unit zoned upstairs/downstairs with one Infinity 19. (We need to switch to one unit.) Contractor proposed single 5T. Carrier Infinity 19 and zoned to replace 3T. down and 2T. up.
After reading, asking questions, etc. for weeks, last night we pulled out old blueprints and a measuring tape, bought the HVAC calculator for $50 and spent the entire evening doing our Manual J. (My husband is an engineer and is very precise.) The house came out to 2362 sq. ft of "conditioned area".
Using HVAC-Calc 4.0 with conditions set to: outside = 95F and129 grains H20; inside: 75F and 50% RH (based on New Orleans which is closest city listed) and using the best estimate of insulation, we came out at a recommendation of 3 1/2 tons.
In trying to understand how the contractor might have arrived at 5T, he changed to outside: 100F and inside: 70F, construction tightness poor (leaky farmhouse), dropped the low e-glass and the foam insulation in exterior walls and added 8 people; but still only got a recommendation of 4 Tons from HVAC-Calc.
Are we missing something?
Does HVAC-Calc give accurate results for New Orleans area?
Do you oversize because you are using one unit, zoning and 2 floors?
Please help us.