My furnace recently started emitting a burning smell, this only occurs after it has been running for 2or more hours. I have had the blower motor replaced even though the repairman said he belived the motor was still okay he did notice while replacing it that the barrings were slightly worn. The strange thing about this odor is you cannot smell it in the basement near the furnace it is the strongest upstairs. We are at a loss to the reason. I have had the frunace for 11 years.