Yearly startup maintenance
Prior to the first fire of the year, the following things should be checked and cleaned as necessary. If the unit has a blower for circulating the warm air, then the blower ducts should be vacuumed out and the fan cleaned.
The draft (combustion) blower and vent pipes should be cleaned with a chimney brush.
It is a good idea to check the door seal by placing a dollar bill between the door and the frame with it closed. Then, pull on the dollar and if you can easily pull it out the gasket needs replaced.