Bigger is not always better!
It’s a serious mistake to buy more air conditioning capacity than you need. For example, a larger A/C will cost more to operate and give you less comfort. Why? Because it will have short “on” and “off” periods, allowing too wide a temperature range. The short “on” periods of an oversize air conditioner will prevent it from removing enough humidity from your home, an important part of its function. An air conditioner that’s too big will result in clamminess and mold formation.
A bigger air conditioner is more powerful but not better for your home. Here’s why… when an air conditioning system runs, it does two jobs. It lowers the temperature of the air, and it removes moisture from the air. In order to remove moisture from the air, the air conditioning system needs to run for a certain amount of time. While the air conditioner is running and the blower motor is pushing air over the indoor coil, or the evaporator, the air temperature will change. As a result, water vapor will condense on the evaporator coil. This occurs in over sized air conditioners too. However, over sized air conditioners don’t run for a long time because they satisfy the thermostat quickly and then shut off. The short cycling of the air conditioner does not remove enough humidity in the home and adds wear and tear on the air conditioner. When an air conditioner is over sized, it starts up and shuts down more frequently because it runs for only a short time to meet the thermostat set point. An air conditioning system that’s too large or too powerful for your home can waste money, energy and comfort.
“Lots of things are better if they’re bigger, like TVs or ice cream cones, but not air conditioning systems,” says Rick Fravel, Contemporary Systems owner. “An A/C unit is supposed to dehumidify the house as well as cool it. A unit that’s too large will turn on and off too quick, bringing the temperature down fast but not removing the humidity. So you’re losing comfort as well.” In your home if your air conditioner runs for only 5 to 10 minutes before shutting off, it’s over sized. If it runs over half an hour, it’s probably sized correctly.
If you’re building a new home or adding an addition, Rick recommends performing a Manual J load calculation to determine the heating and cooling loads. In fact, some counties make the Manual J load calculation mandatory when applying for an HVAC permit.