HOW OFTEN SHOULD I CHANGE MY AIR FILTER?
The filter helps to keep your duct system, motors, and coils clean.  If you have a fiberglass throwaway filter, you should change it every 30 days.  The same applies to electro-static and electronic air filters; you should clean these monthly as well.  I recommend that you change/clean your filter the same time you test your smoke alarm batteries (monthly).

HOW OFTEN SHOULD I HAVE MY SYSTEM CLEANED?
To most people's surprise, airborne dirt and household lint cause the most problems with your system.  Even if you change your filters every month, 90 percent of the airborne particles pass through your throwaway air filter.  These particles will collect on your blower motor, blower wheel and indoor coil.  Air filters help, but particles still get through.  Your outdoor coils collect dust, pollen and grass clippings.  These particles will become an insulator that has a huge effect on the operation of your system. I recommend that your Heating and Air conditioning system be professionally cleaned at least once a year to ensure that it is operating at its fullest potential. GMC uses special coil cleaners to remove all the particles and bacteria that become embedded in your system.