(also posted in alt.hvac... the more opinions the merrier!)

Hi!

I'll start by saying that I know the correct answer is "consult a
professional to do a load calculation", but I've consulted two
professionals who are coming up with much different answers so I'm
feeling stuck.


The house is 2076 square feet, new construction, two-story with most of

the square footage on the ground floor. R-19 insulation in exterior
walls and ground floor joints, R-30 in ceiling. One big air return,
about 12 registers. 2x4 (I'm pretty sure, a slight chance it's 2x6)
frame construction. Furnace in crawl space under house. Have some
large windows in great room and a glass slider in dining room but these

all face north, otherwise normal sized windows. Located in Flagstaff,
AZ, elevation 6900'. Average high temperature in July (the hottest
month): 82 degrees. All-time record high: 97. Humidity: tends to
be quite low.... this is the Southwest. This is a town where most
people don't have A/C, and the unit won't be heavily used. You can
usually get by with your windows open and ceiling fans. It just gets a

little toasty now and then, which is why we want the air.


Once contractor says a 3 ton unit is the way to go, another says 5 ton.

Any opinions regarding who is right?


Thanks!


Tom in PA