Our unit is 21 years old. We have lived in the house for the last 11 years. It looks like the previous owner may have changed the fan/limit control at some time. There is a Honeywell fan/limit manual with the unit. The ventor motor has started to make a noise near the end of this years heating season. If the fan/limit is the only thing changed in 21 years that speaks for it's self. They are no longer making the furnaces in the same factory as they were 21 years ago so I don't know what today's quality is like but I would try a new Keeprite.

Units ok.

Had a Keeprite installed new & it is amazing!!! Only problem I ever had was the furnace shutting on & off which turned out to be the inlet pipe, (very, very important to be sure no leaves, or plastic bags get sucked up into the inlet pipe. Always check the inlet on your high efficiency furnace before you replace any parts. Sometimes condensation or snow can freeze inside an elbow, causing the furnace to shut off. Good tip from a happy Keeprite owner!!!!