There are several steps you can take to maintain your furnace and help extend its life span and efficiency. Do the following at least once a year for proper furnace maintenance: Turn off the electrical power and fuel supply before handling any maintenance work. Vacuum anywhere you see dust and soot, especially in the combustion chamber and blower compartment.  Change the furnace filter as often as you need (usually every three months), depending on its type and furnace usage. Oil the motor bearings. Remove all flammable materials from around the furnace.