The most important maintenance task for both heating and cooling systems is something you can do yourself—replacing the air filter. Check your filter monthly until you see how quickly it gets dirty at different times of the year. Depending on your equipment, your home, and the types of filters you use, you will need to replace it three to six times each year. When a filter has a matting of dirt—i.e., it’s difficult to see through when you hold it up to a light—it’s time to replace it. If you aren’t sure how to tell when a filter is too far gone, ask your technician to show you what to look for during the next service visit.

A dirty filter makes your system work harder than it should, reducing performance and energy efficiency. A dirty filter also makes your system spread dirt throughout your house. An extremely dirty filter can be especially bad for heat pumps and air-conditioners, since it can cause evaporator coils to freeze up and, possibly, cause the compressor to fail.

Gas and Electric Furnaces

Gas and electric furnaces usually need less professional maintenance than other types of equipment. But it can be worthwhile to have a professional visit every year or so to clean and adjust your equipment for the sake of efficiency, and check for existing or potential leaks of fuel or combustion products.

Oil Furnaces

An oil-burning furnace is the piece of equipment most likely to need regular preventive maintenance. Replacing nozzles and oil filters, adjusting excess air levels, and cleaning soot from the firebox can increase heating efficiency by 10 to 12 percent—even more in badly maintained systems. Find an expert who has the equipment and know-how to measure carbon dioxide, flue gas temperature in the stack, “smoke number,” and the stack draft to perform this maintenance. Have the expert also check for dangerous smoke leaks and improper safety shutdown.

If you have a large house, where a few percentage points improvement in oil furnace efficiency would save the cost of a service visit, arrange for a professional to visit annually. But if your house is small, you can skip a year or two between visits.

Air Conditioner/Heat Pump

One task you can do yourself for either an air conditioner or a heat pump is to clear debris away from the outdoor unit. Keep the unit’s grills free of grass clippings, leaves, and other debris which can inhibit airflow. Typically, outdoor units should be installed atop a platform several inches above ground level. If not, have a contractor raise your unit. An obstructed outdoor unit overworks the compressor and can cause a costly premature failure.

Other maintenance tasks are usually performed only by professionals. Condenser coils need to be checked for surface dirt and dust, and cleaned if necessary; contractors often use a special chemical bath for the cleaning. Electrical connections and contacts need to be checked visually, and capacitors should be tested. Controls designed to protect the compressor from high or low pressure should also be tested. Finally, the refrigerant level should be checked, with refrigerant added as necessary.

Under no circumstances add or release refrigerant yourself. As part of U.S. Environmental Protection Agency regulations written to comply with the international ban on ozone-depleting substances, all heating and air-conditioning contractors that handle refrigerant must be trained and certified, and they must possess equipment that will capture the refrigerant and prevent it from escaping into the atmosphere.

Proper maintenance enhances your equipment’s performance, energy efficiency, and durability. If you do the tasks you can do yourself, however, it’s not clear how much benefit professional maintenance service provides.

Contractors will argue in favor of air-conditioner maintenance visits each spring before the cooling season, and heat pump visits each fall. But heating and air-conditioning contractors have an obvious bias: the more visits you pay for, the more money they make, and the better their equipment runs. Best of all from the contractor’s standpoint, maintenance visits take place before peak heating and cooling seasons, providing a welcome flow of revenue and a way to keep technicians busy.

Equipment manufacturers have less reason than contractors to endorse maintenance visits. Although regular maintenance may make manufacturers look good by helping equipment achieve maximum lifespan, performance, and efficiency, a manufacturer can look even better by claiming that its equipment can do without expensive maintenance. Nonetheless, most manufacturers recommend annual professional maintenance of air-conditioning and heat pump systems.

Yet there appears to be little hard data indicating that reductions in energy use or increases in equipment life offset the cost of professional maintenance. Clearly some systems run well despite forgoing years of professional maintenance. And contracting for yearly maintenance visits for air-conditioning equipment, for example, seems rather arbitrary. Why not twice a year, or once every two or three years? Why not more or less often depending on conditions? It is clear, for example, that the need for maintenance is greater if your system is old, heavily used, has much dust and pollen around it, contains aluminum wiring, or frequently breaks down. Also, maintenance is more justified in large houses, where a small percentage improvement in energy efficiency can produce substantial savings.

In the end, decisions on professional maintenance will be much like decisions about how often to change your car’s oil or have your teeth cleaned: There is no absolute right answer. As with those decisions, ask the professional you deal with to explain why a particular maintenance interval is right, given your individual circumstances.

If you don’t plan to have yearly professional air-conditioner or heat pump service, test your system before the usage season begins. That way, if there is a problem, you can order a service visit before the peak-season rush.

Getting a Good Price

It’s not difficult to compare prices for maintenance-only service visits. Call companies that rate high for quality on our Ratings Tables and ask their price for a maintenance-only service visit, assuming no repairs will be needed. Find out exactly what is included in maintenance service. (Will they clean condenser coils, for instance?) Expect to pay between $90 and $125 per visit. But bear in mind that maintenance visits sometimes reveal the need for repairs, so use a high-quality company that charges reasonable prices.