When used in conjunction with natural ventilation, portable box fans are a good solution to cooling houses on hot days. Encased in shallow, metal frames with open-air grid panels covering blades and fan, box fans are essential tools if you don't have or don't want to use air conditioning. Box fans can create indoor air movement, help hot air exit and, with some creation, become swamp coolers and air purifiers.

Cooling a house or apartment through natural ventilation requires methodically closing windows, doors and shades during the heat of day and opening them at night to let in the cool air. Natural ventilation relies on outdoor wind and the chimney effect to cool a house. When cool air enters the basement or first floor, it soaks up heat there, rises upstairs as if traveling through a chimney and exits through upstairs windows.

Box fans placed in or near windows can help draw in cool air from outside or pull warm air out of a room depending on how they are placed. If the blades face the window screen, the fan helps pull hot air out of the room. Flipped the other way, it draws in air from outdoors.

Some homeowners use metal stand fans to help filter air in small spaces. It is possible to make an inexpensive air cleaner for a workshop by attaching a furnace filter to a box fan supported in overhead brackets mounted to floor joists. The fan sucks up the dusty air into the filter. Replace the filter when it becomes too dirty to shake out.

A swamp evaporative air cooler is an air conditioning device that is often installed in roofs of homes in hot, dry climates. Also known as an evaporative cooler, it decreases heat by circulating fine moisture through an entire house. A swamp cooler for a single room can be improvised by placing a large bowl of ice water in front of a box fan blowing into the room.