SMCICT

Look for specific maintenance instructions attached to your furnace housing. Various designs call for different maintenance procedures.
Natural gas furnaces need only simple maintenance. Changing filters regularly, plus oiling the motor and keeping it clean, make for worry-free operation. The whole furnace needs occasional cleaning. Dirt gathers in the furnace closet, around the blower, and inside the furnace housing. Vacuum these areas once a month, when you inspect the filters. Make sure the whole furnace power circuit is off before you vacuum inside the furnace or blower casement. Never use your furnace closet for storage. Remove the registers and vacuum the heating ducts frequently. Wash grimy ducts and registers with detergent.
If you ever smell gas, open the windows to vent the fumes outside. The gas range pilot may have gone out or a burner valve may left open accidentally. If you don’t find the problem there, turn off your main gas valve. Call your gas utility and report a leak. It will receive their immediate attention. Whatever you do, DON’T light match; instant disaster could result. If you live in a mobile home park, call the management too. Get that leak sealed before you use any gas appliance, even if it means eating out or sleeping in a motel day or two. Gas explosions are devastating.