I'm building a new 3400SF w/ additional 500SF bonus room 2-story home in NE Ohio. I have done the load calcs myself, both with an online version and with the HVAC-Calc (homeowner's edition) program I purchased online, and I am puzzled between what I've computed, what I'd expect, and what contractors are bidding.
By the HVAC-Calc program, for the almost 4000SF home, I have come up with a total heat gain of 43,609 BTUH (3.5 ton) and a heat loss of 96,574 BTUH using "average infiltration", 95/5 outdoor temp specs w/ 94 grains of moisture, and 75/72 indoor temps with a 50% RH. (Cleveland, OH)
I was planning on using spray-foam insulation on the 2x4 constructed walls, as well as the ceiling, so when I change from "average infiltration" to "tight, new construction", my heat gain drops to 38,207 BTUH (3 tons). Again, this is for about 4000 SF! As far as I can see, I've entered all the correct info for windows sizes, low-e glass, fireplace, square footage, directional info, and everything.
I'm trying to find out if I've done something wrong, because of the 4 contractors I've had bid the job, 3 have insisted on 5 tons, and 2 have said that a 2-unit system (2.5/3 ton) is REQUIRED for the size of the house. One guy came in at 4 tons (he had the Whirlpool rep do the calculation), but I'm not so sure the other guys have even done the actual calculation (one mentioned the old "rule of thumb" of 1 ton per 800SF...). As a matter of fact, the ones who quoted 5 tons said they'd have me sign off on a release stating that they wouldn't be responsible if I chose to go with a lower tonnage unit.
I was planning on having zone dampers for up/down with a single unit located in the basement. I just want to make sure that what I'm describing (3 to 3 1/2 tons) isn't too crazy sounding for the size of the house, and if I were to have to increase the size, if 4 tons would be a happy medium.
As a side note, I'm wondering about anyone's experience with Heil A/C and furnaces, as well as the new-comer Whirlpool.