mad hatterŪ wrote:
To the OP--
Either get a qualified hvac person to do a load calc or use the rule
of thumb that you need 1 ton per 800 sqft area (for southern climates,
decent insulation, normal ceiling heights) which sounds like what the
contractor is using. You could also talk to others in your area and
see what size homes and ac's they have and with a little math, figure
out what size your's should be. If you are that worried (tho I think
2.5 ton is okay) go with the 3 ton unit.
I guess you didn't read the article.
http://www.proctoreng.com/articles/bigger.html
The "square-foot-per-ton" sizing method avoids calculating the cooling
load of the building and proceeds directly from the square footage of
the building to the size of the air conditioner. No contractor submitted
such a method for approval but a number of contractors reported that
they often used this method, or knew others who did. In a study by the
Florida Solar Energy Center, 25% of the contractors reported that they
size by floor area (see "How They Size Air Conditioning Systems in
Florida," above).
While this approach is rapid and simple, it does not account for
orientation of the walls and windows, the difference in surface area
between a one-story and a two-story home of the same floor area, the
differences in insulation and air leakage between different buildings,
the number of occupants, and many other factors. In some cases
contractors attempt to cover these variables by categorizing the home as
low (a new home in a moderate climate), average, or high (an old home in
a hot climate) but this method also falls short of properly sizing air
conditioners.