Furnace Vent Fan Replacement

We have a builder-grade furnace that came with our house (a Comfort Maker FBF100F14A4).  It’s terribly inefficient, on 80%, and the quality is not so great either.  One component that has to be replaced routinely is the “Furnace Vent Combustion Draft Inducer Motor”.  It’s easy to tell when it needs to be replaced, as it resonates through the duct work sounding like the furnace is going to fall apart.

The vent fan is used to evacuate all the flu gases up the chimney, and since our furnace is 80% efficient, that flu duct-work gets really hot.  As it get’s hotter (especially on really cold days), the fan would get louder.  Before the ignitor does it’s job, the vent fan will spin up creating a slight vacuum that enables a switch through a rubber hose.  Once the switch is made, then the furnace will allow the gas to be ignited.

Replacing the fan is straight forward, only a one tool needed for the job:  A nut driver to remove the mounting screws.  Before getting started, I waited a little after the last cycle so the duct would cool off some.  After a couple minutes, the power switch was flipped to the “off” position.  Now the work can begin.

  • Remove the metal screws that connect the duct to the fan.
  • Remove the four mounting screws.
  • Disconnect the two wires connected to the motor, being careful not to damage the connectors.  They were easily removed without any tools (e.g. pliers).
  • Disconnect the hose.
  • Carefully remove the fan, slight rocking will be required to loosen from duct.
  • On the furnace where the surface mates to the fan housing, there is the remnants of the fiberglass gasket.  Remove that taking care to not drop any pieces inside the furnace.
  • The replacement unit should come with a new fiberglass gasket, install it on the back of the fan.
  • Reverse the process used to remove the fan, making sure all mechanical connections are secure.  Don’t forget to reconnect the hose.
  • Turn the power back on.

In the spring the furnace will be cleaned out with a vacuum, but for now at least the furnace is running quietly again!





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