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For starters, once a year, vacuum out the area around the furnace’s blower.
If possible, also slide out the fan unit, clean each fan blade with a toothbrush, and then vacuum with a brush attachment on a vacuum cleaner.
While you’re at it, look for oil ports on the motor, normally located near the motor shaft. If the motor has these, apply two to three drops of non-detergent motor oil into each port (you may have to remove a cover plate to do this). Though most contemporary motors don’t require lubrication, do lubricate motors with oil ports once a year. For more about maintenance, see Maintenance Checklist for Central Heating Systems.