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Ideally, try placing the box fan in a window that faces the wind. Install the box so that it faces inside the room and pushes cooler air into the space. To make your box fan most effective, close the window as much as possible after you place the box fan in the window. Put the second fan in a higher window if possible, as hot air rises, and set it to blow outwards. Place it in a window that's not facing the wind. Pull the window down to the top of the fan. This process creates a vacuum, drawing air through the room and cooling it down. Reversible fans give you the option of turning the fans around with little to no heavy lifting, so that you can have the coolest room possible. If the space is large, encourage air movement by placing another fan in the middle of the room. The fan should blow towards the fan facing outward to encourage the air to go out.

Summary:
Place a window-mounted box fan facing inward. Place a second window-mounted box fan across the room facing outside. Use reversible fans if the wind in your area changes direction frequently. Add extra fans in the middle of a large room.