The Fasco A331 is a direct-replacement draft inducer blower motor engineered to restore proper combustion air flow in select Fasco and Lennox furnaces. With ball bearing construction, Class B insulation, and thermal overload protection built in, this motor is a reliable drop-in fix when your existing inducer fails -- no rewiring, no fabrication.
Draft inducer motors pull combustion gases through the heat exchanger and out the flue before the main burner ignites. When this motor fails -- or weakens enough to trigger a pressure switch fault -- the furnace locks out on a safety code. The A331 matches the original motor's frame size, wiring harness connectors, and performance specs so you can restore heat quickly.
Also sold under NBK Parts number 20577, this motor is stocked as a service replacement and is compatible with both 50 Hz and 60 Hz power supplies, making it suitable for North American residential and light-commercial furnace applications.
Permanent split capacitor motor provides reliable starting torque and efficient steady-state operation in continuous draft inducer duty.
Ball bearings deliver longer service life and lower friction compared to sleeve-bearing alternatives, especially in the heat of a furnace cabinet.
Internal thermal protector automatically cuts power if the motor overheats, protecting both the motor and the furnace control board.
Rated 2800 RPM at 50 Hz and 3200 RPM at 60 Hz -- one part covers both supply frequencies without special ordering.
The A331 ships with two sets of leads already attached:
These lead lengths and terminal styles are matched to the original Fasco and Lennox harness connectors. In most cases the motor plugs directly into the existing wiring without cutting or splicing.
The A331 uses an open enclosure with an over-air cooling path (open air-over). This is the correct enclosure type for draft inducer applications where the motor sits adjacent to the blower wheel and is cooled by the air stream it moves. The open design is not appropriate for wet or heavily contaminated environments.
Class B insulation is rated to 130 deg C winding temperature, providing adequate thermal margin for the ambient conditions inside a furnace cabinet (rated to 104 deg F / 40 deg C ambient).
The A331 (NBK 20577) is a verified replacement for the following OEM part numbers: