It Pays to Maintain Your A/C

Maintaining your air conditioner can save up to 30 percent on operating costs, protect it from early failure, prevent mold from developing in the system, and help it perform at its best. Follow these tips to save money and protect your health. They'll also keep you cool and comfortable this summer.


A dirty filter restricts airflow; that’s bad for the equipment and the occupants. How often you need to change the filter varies with the type of filter, how much the system runs, and the air inside your home. For a typical home, a standard filter should be changed (or cleaned, if washable) every month. Pleated filters have more surface area and can last two or three months before replacement. Pleated filters cost more, but they capture more and can help to keep your equipment and air cleaner. 

Some filters capture finer particles than others.  A MERV rating is a standardized measure of a filter's efficiency, the higher the number the more it captures.  A MERV 8-10 provides good filtration for most people without overly restricting airflow.  People who suffer from allergies, asthma or other conditions may desire higher MERV ratings but should consult with their HVAC contractor to ensure that the system operation and efficiency will not be impacted.

Be sure that air cannot leak around the filter. Seal gaps around the frame that holds the filter and make sure the return plenum (the path between the filter and the unit) is airtight. Leaky returns and drawing unfiltered air from the walls and attic are major culprits in dirty and moldy air handlers and ducts.

Indoor Unit

The indoor coil, also called the evaporator coil, is located in the inside air conditioner or heat pump cabinet. Air from the home is pulled across the coil for cooling. This can cause the indoor coil to become damp, and moisture attracts dirt and can harbor mold and other contaminants. The blower (fan blades) also collect dirt.

A dirty coil and air handler can endanger your health, waste energy, and cut the capacity of the cooling equipment. Dirty coils reduce airflow through the equipment. For each 10% reduction in airflow, the efficiency of the equipment drops about 5%. Naturally, reduced airflow means less cooling.

The indoor coil should be checked every year and cleaned as needed. This task generally requires a service technician. The indoor coil should be cleaned with a chemical solution; especially dirty coils may require two treatments. The cost of cleaning a coil depends largely on its accessibility. Typically, it will range from $50 to $200 and take one to two hours.

Outdoor Unit

The outdoor unit, also called the condensing unit, contains the condenser coils -- thin fins of metal with refrigerant tubes that discharge heat to the outside air. These coils usually are easy to access and should also be checked annually and chemically cleaned periodically. If the fins become bent, they should be straightened with a special comb. Most service contracts include cleaning and straightening these coils. This takes only about 15 minutes.

The outdoor unit depends on good airflow to work efficiently. It should be clear of tall grass, leaves, and other obstructions. Do not enclose this unit by placing it under a deck or near fencing or dense vegetation. A top-discharge unit (blows air out the top) needs at least two feet of clearance on all sides and 5 feet of clearance above the top. Avoid venting a clothes dryer within 10 feet of the outdoor unit. The lint from the dryer can block airflow, reduce the life of the compressor, and increases your air conditioning cost.

Temperature Check

The difference in temperature between the supply air (coming out of a register) and return air (at the filter) is a good indicator of air conditioning problems. To check the difference, set the thermostat setting low enough to make the air conditioner operate at least 15 minutes while the outside temperature is about 80 degrees. While the unit is running, use an accurate thermometer to measure the temperature of the air at the return and supply register closest. Once the mesaurements are taken, compare the results to the temperature of the inside unit (air handler and blower). The temperature drop from return air to supply air should be 14 to 20 degrees. If it is less than 14 degrees, have your air conditioner serviced.

Duct Leakage

Leaks and losses through the ducts in a vented attic typically account for 30 to 50% percent of a home’s total heating and cooling costs! Duct leaks are often the cause of uncomfortable room air temperatures and can lead to a negative pressure in the home, drawing in more air and moisture, and increasing risk of hidden molds. The best way to check for duct leakage is to have a trained professional  pressure test the ducts with a special instrument that measures the amount of air leakage.

However, if you don’t have access to this service, you can purchase a non-toxic smoke pencil or infrared draft detector online and try a visual inspection. With the unit operating, check around the cabinet, duct joints, connections, return plenum and supply grilles for  leaks (inward or outward). Look for signs of wetness and mold at joints as indicators of cold air leaks.  Often the duct connections are not sealed, or are poorly sealed with duct tape. Have all duct connections sealed with mastic, a thick paste designed this purpose. Never use duct tape to seal a duct.

3/15/2005 8:01:18 AM
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