Efficient Operation of
Air Conditioners

How you operate your air conditioner can make a big difference in what it costs to cool your home.  Here are some tips that can help keep your operating cost low without sacrificing comfort.

Minimize Use - In mild weather, using natural ventilation or fans at night, and keeping the house tightly closed during hot days, is usually less expensive than operating an air conditioner. Use air conditioning only when ventilation can't maintain comfort. During extremely hot, humid times of the year, it is usually more efficient to seal up the home and air condition around the clock. This is because every time the outside air is brought into the home, the air conditioner must work extra hard to remove the moisture in it. For the same reason, if your air conditioner has an option to bring in outside air, use it sparingly. It is far more economical to recirculate and cool the indoor air than to cool the hot outdoor air down to comfortable temperatures and remove the moisture in it.

Seal Up The House - Keep all doors and windows closed tightly when operating an air conditioner. Be sure all air conditioner ducts passing through unconditioned basements, crawl spaces, and especially attics are well sealed and insulated.

Minimize Area Cooled - Don't cool unoccupied rooms, however, with central systems, don't shut off too many registers because closed registers increase system pressure, which can damage the compressor.

Raise Settings and Use Fans - Keep thermostat settings at 78° F or higher. Moving air with ceiling fans can increase the comfort range. And remember, you save 3-5% on air conditioning costs for each degree the thermostat setting is raised.

Reduce Humidity - Another way to improve comfort at warmer temperatures is by reducing humidity. Keep as much moisture out of the house as possible. Run a bathroom exhaust fan while showering, be sure your clothes dryer is vented to the outside, and keep house plants outside during the summer. Most of the water you pour on them ultimately ends up in the air and must be removed by the air conditioner when it is running.

Regular Service - Air conditioners and heat pumps need regular maintenance in order to perform at top efficiency. On room air conditioners, clean the air filters monthly. They should never be allowed to get dirty enough to restrict air flow, which can damage the unit. The condenser should be cleaned by a professional every other year, or even yearly in dusty conditions.

Central air conditioning units should be inspected and tuned by a professional once every two to three years. While servicing your unit, have the refrigerant charge checked. The charge impacts how efficiently your air conditioner operates. A system undercharged by 10% can operate at a 20% lower efficiency and overcharging can damage the unit and reduce its life. The service technician will also check the temperature difference between the air entering and leaving the air conditioner. If it is greater than 12°F, air circulation may be inadequate. The rate of air flow must be matched with the unit's capacity. If the air moves too fast over the cooling coil, it will not be sufficiently dehumidified, and too little air can result in ice forming and blocking the coil.

Shade - To achieve its greatest efficiency, the outside part of a central air conditioner, the compressor and condenser coils, should be located in a cool, shaded place that allows good ventilation. The best place is usually on the north side of the house under a canopy of trees or tall shrubs. Also, try to avoid placing the compressor on the roof or on the east or west side unless it is somehow completely shielded from the summer sun. Sunlight hitting the condenser unit will heat it up and reduce its ability to exchange heat. Be sure bushes and other vegetation do not choke air flow. The compressor needs good air circulation around it to effectively exchange heat with the outside air. Shading the outside portion of a window air conditioner can be tricky, but is worth some effort because the unit will operate more efficiently when it is exchanging heat into a cooler environment.

With heat pumps, because they heat and cool, location of the outside unit is a little more complicated. Heat pump compressors should be located on the south side of the home, especially in colder climates, so they can take advantage of winter solar heat gain. In the summer, it should be shaded with a sunscreen or tall deciduous vegetation.

Turn It Off - At the end of the cooling season, turn your air conditioner off. Left on, the heating elements in the unit could consume energy all winter long. Simply flip the circuit breaker to turn it off if the unit doesn't have its own switch. Turn the power back on a day or so before starting up the unit to prevent damage to the compressor.