A multiple fan array system for use in conditioning air in a structure by drawing air from an inlet area and expelling it into a discharge area, the multiple fan array system comprising: at least two fans, each fan having an inlet and an outlet and being operable to draw air in through the inlet and expel air out through the outlet; and a backflow preventer operatively associated with each of the at least two fans, each backflow preventer comprising: a main body having a top wall, a bottom wall, and opposed side walls extending between the top and bottom walls, the main body defining an open front end and an open rear end, the main body being attached to one of the at least two fans adjacent the inlet of the one fan such that air flowing into the inlet must first pass through the main body; and a pair of doors attached to the main body, each door being hingedly attached to one of the opposed side walls for pivoting about the vertical axis, the doors being configured for movement between an open position in which air is permitted to enter through the open front end to be drawn into the fan inlet and a closed position in which air is prevented from entering through the open front end to be drawn into the fan inlet; wherein the doors of each backflow preventer in the open position form a tapered intake passageway having a wider opening adjacent the open front end and a smaller opening adjacent the open rear end. at least two fans, each fan having an inlet and an outlet and being operable to draw air in through the inlet and expel air out through the outlet; and a backflow preventer operatively associated with each of the at least two fans, each backflow preventer comprising: a main body having a top wall, a bottom wall, and opposed side walls extending between the top and bottom walls, the main body defining an open front end and an open rear end, the main body being attached to one of the at least two fans adjacent the inlet of the one fan such that air flowing into the inlet must first pass through the main body; and a pair of doors attached to the main body, each door being hingedly attached to one of the opposed side walls for pivoting about the vertical axis, the doors being configured for movement between an open position in which air is permitted to enter through the open front end to be drawn into the fan inlet and a closed position in which air is prevented from entering through the open front end to be drawn into the fan inlet; a main body having a top wall, a bottom wall, and opposed side walls extending between the top and bottom walls, the main body defining an open front end and an open rear end, the main body being attached to one of the at least two fans adjacent the inlet of the one fan such that air flowing into the inlet must first pass through the main body; and a pair of doors attached to the main body, each door being hingedly attached to one of the opposed side walls for pivoting about the vertical axis, the doors being configured for movement between an open position in which air is permitted to enter through the open front end to be drawn into the fan inlet and a closed position in which air is prevented from entering through the open front end to be drawn into the fan inlet; wherein the doors of each backflow preventer in the open position form a tapered intake passageway having a wider opening adjacent the open front end and a smaller opening adjacent the open rear end.