In order to determine exactly how big or small your home’s heating or air conditioning system should be, your HVAC contractor needs to calculate the system’s heating and cooling capacity in relation to indoor comfort. The result is called the “load” of the home. A home’s load is partly dependent upon its square footage, but a true load calculation goes beyond that to include the building’s construction; orientation to the sun; R-value (a measurement of thermal resistance) of the insulation; number, size and placement of rooms, windows and doors; thermal efficiency of windows and doors; number and arrangement of floors; and climate.
Residential load calculations make use of mathematical formulas that take all these variables into consideration. Determining the load by using non-mathematical methods almost always leads to installing an oversized system, which results in increased initial costs, monthly utility bills and maintenance. It can also shorten the lifespan of the equipment by making it cycle on and off too frequently.
Who does the load calculation?
Your HVAC contractor should be able to perform a load calculation—the process has been computerized in recent years, so it’s not as time-consuming as it was in the past. If the contractor says it isn’t necessary, you may want to look elsewhere. In some areas, local utility companies will perform load calculations.
Why is it important to have a correctly sized HVAC system?
Having an improperly sized heating or cooling system can lead to multiple problems. Your cooling load consists of two parts: the temperature of the air (the sensible load) and the moisture or humidity in the air (the latent load). An oversized cooling system cools down the temperature very quickly, but it doesn’t run long enough to remove sufficient moisture from the air. Many people turn down the thermostat to make the air conditioner run longer, which increases utility costs. In some cases, the insufficient moisture removal resulting from oversized cooling equipment can lead to mold growth and other types of moisture-related damage.
A correctly sized cooling system runs long enough to “wring” moisture out of the air. This will allow you to be comfortable at a slightly higher thermostat setting and save you money on your utility bills. It’ll also take care of “mugginess” without making you feel too cold.
