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Office of Energy Efficiency Links


Personal: Residential


Cooling and Ventilation Equipment -
Central Air Conditioners

Operating Tips

A central air conditioner uses a great deal of energy, but you can still promote energy efficiency as you use it. Selecting an energy-efficient air conditioner is the first step in reducing your energy costs.

Follow these steps for more savings:

  • Do not block the air conditioner vents with drapes or furniture.
  • Set the indoor thermostat between 25°C and 27°C, depending on your comfort requirements. A setting at the higher end of the range will result in lower air-conditioning costs. If the humidity level is lower, temperature settings can be at the higher end. Humidity levels can be reduced by using a bathroom exhaust fan when you bathe or shower and an outside-vented range-hood fan when cooking on the range top.
  • Use central air conditioning only when ventilation is inadequate to ensure comfort. One effective approach is to use the natural ventilation of the house at night, when it is relatively cool, and to run the central air conditioner only during hot days, with the house closed up.
  • Continuous indoor fan operation can keep the temperature more uniform throughout the house by eliminating temperature differences due to stratification. It can also help keep the air cleaner, especially if there is an electronic air cleaner installed.
  • However, continuous indoor fan operation can result in higher operating costs than with on-off or automatic fan operation. In more humid climates, the moisture removed during compressor operation is re-evaporated by the fan operation when the compressor is off. This can increase humidity levels and cause discomfort.
  • Adjust the thermostat to save energy and reduce operating costs. If the house is unoccupied for more than four hours, the thermostat should be set at about 28°C. Shut off the cooling system when the house will be unoccupied for more than 24 hours. An automatic programmable thermostat will reliably adjust the temperature for you to help you save money on cooling costs.
  • Turn off the power to the central unit when the cooling season ends. Most central air conditioners have a small electric heater on the compressor to keep refrigerant out of the lubricating oil. Flip the circuit breaker to turn this heater off. To prevent damage to the compressor, remember to turn the power back on a day or two before you need to operate the central air conditioner.
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Maintenance Tips

Proper maintenance is critical in ensuring that your central air conditioner will operate efficiently and have a long service life. You can do some of the simple maintenance yourself, but a competent service contractor should inspect your unit periodically, preferably just prior to the cooling season.

Filter and coil maintenance can have a dramatic impact on system performance and service life. Dirty filters and dirty indoor and outdoor coils and fans reduce airflow through the system. This reduction in airflow decreases system efficiency and capacity and can lead to expensive compressor damage if left for an extended period of time.

Furnace filters should be inspected and cleaned or replaced, depending on the type of furnace and the furnace manufacturer's instructions. The outdoor coil should be vacuumed or brushed clean to keep it clear of dirt, leaves and grass clippings. It can be carefully cleaned with a garden hose after debris is vacuumed off. Consider a professional cleaning if the outdoor coil becomes badly plugged.

Both the furnace fan and outdoor unit fan should be cleaned and lubricated where applicable and following the manufacturer's instructions. Check and adjust the furnace-fan speed at the same time to ensure peak performance.

Ductwork can be professionally cleaned if needed, but the need for cleaning can be reduced by a proper filter replacement and cleaning routine. To ensure that all ducts are airtight, seal the joints with a special duct mastic (sealant). This should reduce or eliminate air leaks. High-temperature duct tape may work, although it tends to degrade or permit air leaks over time. Be sure that vents and registers are not blocked by furniture, carpets or other tems that can impede airflow. Extended periods of inadequate airflow can lead to compressor damage. For professional cleaning or supplies, look in the Yellow PagesTM under "Furnaces – Heating" or "Furnaces – Supplies and Parts."

Using a high-efficiency air cleaner on a central cooling/heating system is one way of ensuring a clean indoor coil and a cleaner indoor environment.

Hire a competent service contractor to undertake more difficult maintenance or service, such as annually checking the refrigerant level and making electrical or mechanical checks and adjustments.

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