Ventilation system

A ventilation fan assembly comprising:

• a housing having at least one sidewall defining an interior space, an inlet opening into the interior space, and an outlet aperture spaced apart from the inlet, wherein the housing is configured to contain a blower assembly in the interior space;
• a backdraft damper configured to be coupled to the housing adjacent to the outlet aperture, the backdraft damper comprising,
• a main body having a wall defining an inner surface, an outer surface, a first open end and a second open end;
• an interior space defined by the main body wall inner surface;
• a damper door rotationally coupled to the main body wall and located within the interior space;
• the damper door defining a perimeter edge and configured to rotate between (i) a closed position, in which the perimeter edge is located adjacent to the main body inner surface, and (ii) an open position in which a majority of the perimeter edge is not adjacent to the main body inner surface;
• wherein the damper door is rotationally biased to the closed position;
• a block extending from the main body wall inner surface into the interior space adjacent to the damper door perimeter edge when the damper door is in the closed position.