A diverter duct for a ventilation system includes a main body defining an inner surface, a first portion including an inlet, a second portion located downstream of the first portion, a third portion including an outlet, an opening located between the first portion and the third portion, and an air deflector positioned within the main body downstream of the first portion to deflect a portion of the air from the inlet of the main body towards the opening. A first contoured section is formed in the first portion of the main body. The first contoured section may direct air received from the inlet towards the opening at a first operating condition. A method of installing the diverter duct includes coupling the inlet with an upstream fan, and coupling the outlet with an outlet fan, such that selective operation of the inlet and outlet fans cause vary airflow though the outlet or the opening.