A traditional home comfort system (known as a "split system") has three parts: an indoor furnace/air handler (which circulates the indoor air), an indoor evaporator coil (which removes heat from the indoor air), and an outdoor condensing unit, better known as "the air conditioner." Air conditioners cool the house by removing the heat absorbed by the indoor evaporator coil.

All three units should be matched and designed to work together to get maximum efficiency and longer system life. The Seasonal Energy Efficiency Ratio (SEER) is a measure of the cooling efficiency of your air conditioner. The higher the SEER number, the more efficient the system (similar to gas mileage in a car).