Cost: $200-$300, depending on where you live.
How often: at least once a year.
When: spring or fall. Heating, ventilation and air conditioning, or HVAC, companies aren't as busy, and you're not in dire need of heat or air conditioning.
What an inspection might find:
The furnace blower is not working properly. Cost to repair or replace: $100-$150. Possible consequence of letting it go: a broken heat exchanger. Potential savings down the road: $300-$1,000 to replace the heat exchanger or $750-$3,500, depending on the energy efficiency, to replace indoor or outdoor furnace components.
The reversing switch in the heat pump is broken. Cost to repair or replace: $100-$300. Letting it go results in no heat from the heat pump, and the system switches to a more expensive auxiliary heat. Potential savings: lower heating bills.
Bottom line: "Things that happen often happen at the worst possible time in the worse possible conditions and you're looking at the maximum rate," says Terry Townsend of Townsend Engineering in Chattanooga, Tenn., and former president of the American Society of Heating, Refrigerating and Air-Conditioning Engineers. Remember, continual maintenance prolongs the life of the equipment. "You're sitting there with an investment of thousands in your HVAC system and you're investing a few hundred dollars in maintenance."