Nothing in your house affects your comfort more than your heating and cooling systems. Yet unless the heater conks out during a blizzard or the air-conditioning goes on the fritz in the middle of a heat wave, most of us pretty much ignore our heating, ventilation and air-conditioning (HVAC) equipment. We shouldn't. When it's not kept in shape, even the best system can cost you. How much? Depending on how you heat and cool your home and the climate of the area you live in, clogged filters, dirty thermostats, sooty flues, leaky ductwork and unlubricated fan motors can reduce heating and cooling efficiency by up to 25 percent. Some of these maintenance tasks are simple, while others require a trained pro. You'll also need an HVAC contractor if your system is at the end of its useful life. Here are some tips for dealing with HVAC equipment and the pros that service it. Routine Maintenance The good news here is that some systems require little attention. A heat pump only needs a yearly service call by a technician who will check belts and filters and replace them as needed. He should also oil moving parts and inspect the wiring. A gas-fired, forced-air heating system has simple requirements too. Furnace filter should be changed every month or two during heating season, and the circulating fan oiled once a year. Call in a pro to check the heat exchanger, flue and ducts and to adjust the burner every other year. Other systems, like an oil-fired boiler, require annual maintenance—flue cleaning, a fuel-filter change, cleaning and adjustment of the jets—and often need attention more often than that. These chores should be handled by a professional. Air-conditioning units are a little less maintenance-intensive. At the beginning and end of each cooling season, you should clean or replace the filters, vacuum out the unit and lubricate the motor. If the unit is not cooling properly, call a technician to check the pressure level of the refrigerant. Arrange for service calls before the start of heating or cooling season. You'll get better attention and have more flexibility when scheduling the appointment. When hunting for a company to maintain your system, look for one that designs, installs and services the type of system you have. Full-service companies tend to be up to date on the latest advances in the field. Besides checking that liability insurance and workers' compensation policies are in force — standard operating procedure with any hire — check with neighbors, friends and family who have used the company over several years. How did the system run under the company's care? Did the technicians always leave the working area clean? How quickly did the contractor respond to emergencies? Were the service people punctual when you called with a problem? A quality provider will have an emergency number that's staffed 24 hours a day, seven days a week and enough technicians to respond when the weather is awful and the calls pile up.