An electric forced air furnace's filter should be cleaned or replaced every month during heating seasons and once every three months for the rest of the year. A technician should also inspect and service the furnace once every year.
It is important to perform maintenance on a forced air furnace to prevent higher energy bills and repair costs as well as increase the appliance's life and heating efficiency. When not cleaned often enough, the system becomes clogged, forcing the furnace to work harder and run longer in order to produce heat. Some filters can be washed and reused, but some must be replaced.