Which way do I go

Questioner: Leroy
Category: Heating, Air Conditioning, Fridge, HVAC
Private: No

Subject: inducer fan running backwards
Question: QUESTION: While helping a friend replace the main fan motor of his gas furnace, I noticed that the inducer fan was turning the wrong direction. The unit had been operating like this for approx 6 years. we switched the wires, and the fan ran in the correct direction (verified by checking the airflow at the flue). what are the issues with this condition? was it pushing the exhaust into the house? are their efficiency issues? how could it have operated all this time with that condition?
thanks!

ANSWER: It wasn't doing anything just spinning and I cannot imagine the furnace working like that so it must be a recent failure. If it is a capacitor motor (PSC) then the capacitor may be bad if it is a shaded pole motor (no cap) they will do that sometimes you need to go ahead and replace the motor as it will fail soon.

---------- FOLLOW-UP ----------

QUESTION: This wasn't a recent failure... it has been operating like this for 6 years. we swapped the wires on the draft inducer fan motor and it was definitely pushing the air up the flue. only the main blower motor has a capacitor. We replaced both the main fan motor and its capacitor, and only after we checked that the new blower motor was working properly and everything was spinning down did I notice that the draft inducer fan was spinning in the wrong direction.

ANSWER: Like I said I have a hard time believing a furnace would run for 6 minutes let alone 6 years with a draft inducer running in the reverse direction.

---------- FOLLOW-UP ----------

QUESTION: I know it is hard to believe, but we both saw it spin the wrong direction. We switched the wires (there are only two wires for that motor) and when we started the heat cycle, it was turning the correct direction. we removed the sheet metal flue and could feel that it was in fact blowing out the vent. the only thing we didn't do was reverse the wires again (to their original configuration) to check the air flow at the vent.

Answer: I am not questioning that is was turning backwards, as I said shaded pole motors often do this when they are getting ready to fail. I just think it happened recently. A draft inducer utilizes a wheel instead of a propeller blade and if you turn a wheel backwards it doesn't move any air at all as the horizontal blades on the outside of the wheel are turning against the outside of the curve instead of the inside, it is like trying to shovel sand with the back of the shovel, it's easier to do but not quite as effective.