Owner Maintenance of Forced-Air Heating Systems

Cleaning or Changing the Air Filter

Important! Turn off the power to the furnace before opening the furnace access panel to check the filter or fan.


Few homeowners give the air filter in a furnace the attention it needs. It should be cleaned or replaced once a month. You can get permanent filters made of aluminum or plastic mesh that can be washed in a laundry tub, but these are not as fine as glass-fibre filters and do not trap as much dirt.

If you have added an electrostatic air filter to your furnace, you do not need a standard filter as well. Don’t forget that the electrostatic filters also need to be cleaned regularly; check your owner’s manual for instructions. To maintain clean ducts consider duct cleaning every few years.

Fan Care

Except for superficial vacuuming, there is no maintenance that a homeowner can perform on a direct-drive furnace fan with an internal motor. On belt-driven fans, some motors have small oiling cups over the bearings on each end of the motor, while others are maintenance-free. The ones requiring oiling should be given a few drops of oil once or twice during the heating season and again in the summer, if you use your fan for ventilation or air conditioning. (Check your owner’s manual or ask your furnace serviceperson about the type and quantity of oil to use.)

Also check the tension of the fan belt by pressing it firmly in the centre with your thumb. You should be able to depress it about 20 mm (3/4 in.) and no more than 25 mm (1 in.). The tension of the fan belt can be adjusted by loosening the bolts on the motor mount and moving it forward or backward. Make sure the fan and motor pulleys remain perfectly aligned. This job is best done by a qualified serviceperson.

Care of the Distribution System

Remove obstructions from ductwork, warm air registers and cold air returns so that air can move freely around the system. Use a special water-based duct mastic to seal cracks at duct joints,  At the same time, consider insulating as much of your warm air ducts as you can easily access.

Furnace filters.

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