Intertherm Furnace Blower Motor Fan & Housing Assembly Tested & Working. From an oil downdraft furnace, 1050 RPM GE motor 1/8 HP. Duct Dimensions 10″x 7″. Overall height is 15” length 17 1/2” x width 10′. Its easier to change the whole blower than try and replace the motor. MATCH THE WIDTH, MATCH THE BLOWER. TYPICALLY, ALL BLOWERS HAVE THE SAME DIMENSIONS, EXCEPT AS THE BLOWER GETS BIGGER, IT GETS WIDER. MOST ALL BLOWERS HAVE AN AIR OPENING THAT IS 11 1/2 TO 12 INCHES LONG.