You're not the only one who needs a checkup once each year—your furnace does too. In addition to ensuring problem-free performance at peak efficiency, regular service also helps the appliance fulfill its estimated useful life expectancy. The HVAC technician should inspect each furnace component individually, making repairs as necessary, while also cleaning or replacing the filter. As the furnace filter goes a long way toward supporting indoor air quality and protecting the internal workings of the furnace itself, the technician may suggest that you clean or replace the filter on your own, perhaps as often as every three months. Be sure to ask.