Will 2.5 ton air conditioner cool 3100 square feet?

Answer 1

The rule of thumb is 2.5 tons per 1000 sq ft. so you will need at least 4.5 tons to do the job but I would go larger so the unit is not over worked.

It is just as bad a mistake to oversize a unit as it is to undersize it. An a/c unit which is too large for a house will turn on and cool it down quickly. As a result the house would be cool and humid, The unit needs to be properly sized so as to run long enough to de- humidify the house before it reaches temperature.

I agree, the rule of thumb in the first answer is close for an average. But in order to arrive at 4.5 tons for 3100 sq feet, he either did not use his own rule of thumb or his math is wrong.

You might also search wikianswers for somehting like "How_many_square_feet_does_a_one_ton_central_air_unit_cool"

There are rules of thumb to get an idea of how big an AC system needs to be but they are not intended to be used for design purposes at all. The answer which stated that the size being too big or small is ABSOLUTELY CORRECT. To properly size an A/C system a load calculation needs to be performed by "qualified" individuals who will be considering the style of the structure (i.e. multi level vs. single), the number of windows, door and openings, the R value of all surfaces including windows and doors, lighting load, occupancy load, set point of space versus outside conditions. The Btu's required to cool a space is a complex calculation but is critical to a well installed, good operating efficient cooling/heating system.