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 improvisation, 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. Natural ventilation works well in "climates with cool summers or cool nights and regular breezes," according to the National Renewable Energy Laboratory of the U.S. Department of Energy. Despite its many microclimates, the San Francisco Bay Area overall has mild humidity, another characteristic that makes natural ventilation work well.
Adding Box Fans
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. According to the U.S. Environmental Protection Agency fans, in general, save energy and are an inexpensive alternative to air conditioning. But the EPA notes you need to consider the entry of humidity, pollen and dust when using box fans in or near windows. While the motors of true window fans are rain resistant, box fans improvised as window fans do not have the same protection and should not be placed directly in windows.
Filtering Dusty Air
Some homeowners use box fans to help filter air in small spaces. According to the Woodworking Tips website, 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.
Improvising a Swamp Cooler
A swamp 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 a 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. The Good Human website suggests placing refreezable ice packs in a bowl of cold water and rotating them back into your freezer when they thaw.
- U.S. Department of Energy: National Renewable Energy Laboratory: Cooling Your Home with Fans and Ventilation
- Linhai East-Ocean Industrial Co., Ltd.: What Is a Box Fan?
- U.S. Environmental Protection Agency: Reducing Energy Use
- General Electric: Frequently Asked Questions: Fans
- Woodworking Tips: Box Fan Filter
- The Good Human: Cooling Down Your Space Without Air Conditioning
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