Furnace Maintainance

Check filters.
Check burners.
Clean and lube blower
Make sure the burners light smoothly.
Check the temperature rise to ensure that its within the limits listed by the
manufacturer.
On newer furnaces, which prove the flame-by-flame rectification principle, measure the flame current.
Check vent motor performance.
Inspect the vent system.
Check fresh air ventilation
Check the heat exchanger for cracks, corrosion, or sooting.
Check out the humidifier and electronic air cleaner for proper operation.

Are there any abnormal noises?
How are your utility bills?
Are there any hot or cold areas?