Clean or replace the furnace filter. The filter should be replaced monthly during the heating season. Check the belt between the blower and the motor and replace it if it is frayed or worn. Clean and oil the blower motor, first making sure that the power is off. Clean the blower monthly to remove dust accumulations from the blades and motor body.
Vacuum register grilles and gently clean the thermostat.
Looks for obstructions, cracks, or other deterioration. Check burner performance and adjust if necessary. Clean burners to maintain efficiency and safety. For oil systems, check the fuel supply and the filter in the fuel supply line. Look for and remove any dirt, soot, or rust in the heat exchanger.