Checking Your AC for Efficiency

Whether you’re trying to get a handle on your summer energy bills or ensure you’re cool as a cucumber during that August heat wave (and probably both), you might want to be sure your AC is operating as efficiently as possible. Here’s an easy test to see if your unit is performing up to par.

Change Your Filter

Begin by installing a new air filter – a dirty or clogged filter can have a major influence on how efficiently your air conditioner does its job. Dirty filters mean wasted energy, which of course equals wasted money. A dirty filter may also lead to ice developing on the evaporator coils, preventing your AC from producing cooling air.


When the outside temperature reaches 80 degrees Fahrenheit or higher, set your thermostat a few degrees below the current room temperature. Let the AC run long enough to reach the set temperature, then place a home thermometer inside one of your AC’s air ducts closest to the unit. After 10 minutes, record the temperature reading. Next, locate the unit’s return air duct and use the thermometer to obtain the temperature inside there. Subtract the first number from the second. The difference should fall in a range between 14 and 20 degrees. If the difference is less than 14 degrees, your air conditioning unit may be low on refrigerant or have leaks and therefore be running inefficiently; a difference greater than 20 degrees could indicate a severe blockage. In either case, a call to a qualified repair person is in order.

Even if your test results fall within the “efficient“ range, there are other factors that may be causing your system to work harder than necessary. Although your AC may be in top shape, a lack of adequate insulation in the walls or ceiling and/or poor seals around the doors and windows could have your system straining to cool the outside as well as in. A certified home energy inspector can tell you where improvements need to be made.

Quick Fixes

There are also a few inexpensive actions you can take to keep the system from working any harder than it has to.

  • Install blinds and shades on any windows receiving direct sunlight throughout the day.
  • Turn off the unit and open doors and windows during cooler times of the day.
  • Use the unit fan and portable fans to draw in cooler outside air and increase circulation.
  • Avoid heat-generating activities like cooking and doing laundry during peak heat hours.
  • Use a warmer thermostat setting when the house is unoccupied.

Keep it Clean

Lastly, as your AC system operates, it accumulates dirt and dust in areas that affect its efficiency. Left unchecked, your system can lose as much as 5 percent of its operating efficiency each year due to this buildup, meaning it can’t cool your home as well as it could if it were clean. Most heating & air conditioning companies offer reasonably-priced preventive maintenance services that ensure your system operates at peak efficiency and is ready to keep you as cool as you desire when you need it most.