Change the filter. Dirty filters kill your AC’s efficiency, so replace it once a month for central and window units, or clean them if they’re the washable type. Look for the filter’s minimum efficiency reporting value, or MERV, which ranges from 1 to 12 for home air conditioners. The higher the number, the better filtration it provides.
Fix air leaks. Ducts can lose up to 30% of airflow. To find leaks on a window unit, light a stick of incense and hold it where the unit and the window frame meet; for central units, hold the stick near duct connections. If the smoke blows around, then a leak is present. For ductwork, use foil tape to seal small gaps and duct mastic for larger ones. For window AC units, stuff foam between the device and the window frame; taping is essential.
Use a timer. Why use the A/C to its full potential while at work? For central units, install a programmable thermostat to set higher temperature when away and cooler temperature once you’re home. Newer window units have built-in timers and adjustable thermostats; make sure it matches your device’s voltage. Even if you’re going to be gone for awhile, do not shut off the system because the air compressor will need to work harder to cool your house later.
Insulation is key. Ducts in hot attics or crawl spaces should be wrapped to keep the cool air in. You can use spray foam, batt insulation, or rigid-foam insulation. Seal batt and rigid insulation with foil tape only. Many people make the mistake of using duct tape, which is inefficient.
Keep the compressor and condenser free of obstructions. A central A/C system’s air compressor and condenser are usually located outside the house. It works best when there’s about 2 feet of space in all directions, so get rid of nearby shrubbery. Build a screen to protect condensers or window units from the sun, as direct sunlight reduces their efficiency by as much as 10%.
Don’t make it work so hard. It’s recommended to keep blinds or shades down during the day; installing awnings is also a good solution for shielding windows that face south. Use portable and/or ceiling fans while the air conditioner is on for better circulation of cool air.
Get a professional on maintenance. The dealer who installed your central A/C should put you on a yearly cleaning schedule. Schedule a checkup before the cooling season starts and make sure it includes cleaning and inspecting coils, cleaning / replacing filters, adjusting and replacing fan belts, lubricating motors and bearings, cleaning and checking blowers and fans, inspecting controls and safeties, checking refrigerant and pressures, and verifying operating temperatures.
Don’t close off rooms. Too many closed doors can cause central A/C systems to be unbalanced, resulting in less airflow in the entire house. It’s better to keep doors partially or fully open instead.
Consider an upgrade. For central A/C, look for the seasonal energy-efficiency ratio, or SEER. For window units, the measure is called the energy-efficiency ratio, or EER. The standards mandate a SEER of 13 and an EER of 8, but devices with higher numbers will cost less to operate.