How do you determine what tonnage air conditioner you need?

Answer 1

You measure the volume of every room that needs to be cooled, add the effect of warm air entering through doors and windows, factor in the amount of insulation in the attic and in the walls, determine the average and the peak difference in temperature between inside and outside, and presto - you have enough information to run the calculations. Two tons is enough for my 2,200 square foot home in north Idaho with pretty good insulation, and a temperature average difference of 20 degrees and a 35 degrees peak, and double-glazed sealed windows.