The proper way to size an air conditioning system is with Manual J load calculation program, which is a calculation used to determine the heating and cooling loads of a home or building. This determines how much heating and cooling a house actually needs. It used to be performed by engineers with pen, paper, and slide rules – now it’s almost always done with computer programs.
Would you buy a pair of pants twice your size so you have that extra capacity just in case you might need it? This happens all the time…
Because HVAC load calculations require time and attention to detail, most HVAC contractors rely on rules of thumb to determine the sizes of the cooling systems they install. Usually it’s based on square footage of conditioned floor area, and contractors in many areas generally use 400 to 600 square feet per ton as their rule. But every house is different. Even the same house rotated ninety degrees could vary in cooling load by 25% or more.
You may think to cover all your bases it would be safer to just purchase a bigger system, but this is not always true when it comes to air conditioning systems. Why not? The following are undesirable results of the wrong system installed:
A clammy house because the system isn’t running long enough to dehumidify the air, and in FLorida humidity is no joke!
Shorter lifetime for the system because it turns on and off frequently (also called short cycling). Since it’s so big, it doesn’t take long to cool off the house.
More expensive to install. That extra size isn’t free!