Some tasks on a gas furnace belong in your hands. Others belong to a licensed technician, and the line between them matters for safety and for your paperwork. For how the unit ages over its life, see the gas furnace page.
What stays with you
Check the air filter on the schedule the filter itself lists, and replace it with the same size, with the airflow arrow pointing the right way. Keep the area around the furnace clear of stored boxes and cleaning supplies. Keep the outdoor vent termination free of leaves, snow, and debris. Keep the thermostat batteries fresh. Write each task in a log with the date you did it, since many warranties ask for proof of routine care.
What goes to a pro
Burner cleaning, gas valve checks, heat exchanger inspection, flue and draft testing, igniter or sensor replacement, and any gas line work belong to a licensed heating technician. Do not open the gas valve housing or the burner compartment to make a repair. Do not try to adjust gas pressure yourself.
If you smell gas
Leave the house, leave the door open behind you if it is safe, and call the gas utility or emergency line from outside. Do not run switches or appliances inside the building. This is the one task that never waits.
Plan the visit
Use the fall furnace walk-through to set the pro visit before the heating season starts. Ask the technician to note what they cleaned, tested, and replaced. Keep that note with the warranty file, since it shows the maintenance conditions were met.