Use Window Fans for Home Cooling

Electric fans can be an inexpensive, Earth-friendly alternative to supplement or even replace air conditioning. The best application for window fans is in areas and seasons when it is hot during the day and cool and dry at night. The object is to cool the house with window fans during the night using outside air, which can delay or even eliminate turning on the air conditioner during the day when the window fans are removed. Since this method uses electricity at night instead of during peak usage during the day, it can also help in areas subject to electricity blackouts. To use window fans for home-cooling, follow these guidelines.

Steps

  1. Evaluate if your situation is appropriate for this cooling method.
    • If the temperature is uncomfortably hot and/or humid both day and night, then this method isn't appropriate for you. If this is only the case during the day, a window fan can be successfully used to bring the temperature down at night.
    • If you live in a very polluted area, using a window fan will pull this pollution inside.
    • Window fan ventilation is not recommended for those without adequate window screens, as insects or animals may enter through the open windows. Gnats and other small insects often get in right through window screens, so be prepared to accept that or don't use this method.
    • In high Fight Crime areas, windows accessible from the outside are also likely to be used as a means of entrance by criminals.
    • Noises outside the home will also become louder inside with the window open, although the fan noise may mask some of this.
  2. Choose your fan(s). Ideally, each fan should be the largest that will fit inside the window. Avoid fans that are too large for the window, as positioning them near the window, outside the window frame, frequently results in their falling over. Your house should have an approximately even capacity blowing inward as outward (bearing in mind that smaller, less powerful fans should be counted as a portion of a fan for calculation purposes). If you have an uneven capacity that can't be balanced, it's better to have more blowing inward, as that creates a slight positive pressure inside the home, which prevents carrying dust and insects in when doors are opened and stops "bad air" from backing down chimneys.
  3. Decide on the placement of window fans. This will also determine which fans will blow inward and which outward. There are many considerations here:
    • Blow inward on the coolest sides of the house. This will typically be the sides in shade.
    • Work with the prevailing wind direction, pointing fans in the same direction as the wind blows, rather than fighting the wind. On days when the wind is strong enough, you may not even need the fans.
    • In a single-story flat, arrange fans to blow inward on one side of the house and outward on the opposite side, with the doors open in between for maximum air flow.
    • For multi-story houses, another option is to use the fact that heat rises to assist the air flow by blowing cool air into the lower floors and hot air out of the upper floors, including the attic (with the attic door left open if possible).
    • Avoid blowing inward near garbage cans or parking areas, where fumes and odors may enter the house. Air intake near trees or plants often provides pleasant smelling air, unless pollen presents a problem.
    • Fans blowing inward toward a refrigerator/freezer may blow cool air out quicker than usual (when open), thus increasing the load on the device, so avoid this.
    • Bear in mind that an inward blowing fan may disrupt loose papers, so avoid this in areas like a home office, or secure all papers first.
    • Avoid placing inward blowing window fans above valuable items, like an antique desk or expensive oriental rug, to prevent water damage.
    • Rooms with fans blowing inward will both seem cooler (due to the increased circulation) and will cool down quicker than rooms with fans blowing out.
  4. Place fans in windows. Close the window as tightly as possible around the fan to hold it in place and prevent local circulation. Local circulation is where the same air blown through the fan then goes back around the fan and gets sucked back in, repeating the cycle indefinitely. This just results in the motor warming the air.
  5. Mask window gaps adjacent to the fan. If the fan is blowing inward, the air will want to go back out around the fan due to a local pressure increase. Placing drapes or even paper at the sides of the fan will often work in this case, since they will be suctioned to the window screen. Fans blowing outward are more difficult to mask, as the air around them will want to blow inward. You could place paper or cardboard on the outside of the window, if it's accessible, or tape it down on the inside. Or, you could opt to skip the masking in this case and accept the lower efficiency instead.
  6. Turn on window fans whenever it is cooler outside than inside. Turn them off, remove the fans and close the windows when the house is cool enough to offset the predicted daytime temperature. A general rule of thumb is that the inside daytime temperature will be the average of the outside daytime temperature and the inside nighttime temperature. So, if you want to keep the inside temp down to {{safesubst:#invoke:convert|convert}} and are expecting a high of 80 degrees outside, you need to lower the inside temp to 60 degrees at night. This will vary from home to home, but you can use this rule of thumb until you figure out the formula for your area. In this example, the fans could be turned off once the inside temperature dropped below 60.

Tips

  • Close drapes or blinds when the fans are removed from the window during the day, to reduce solar heating.
  • Some security doors used in high crime areas have screens. If the security door is dead bolted, it can be used as a safe, secure screen to allow air in. If a fireplace fan is used as a whole house fan to exhaust the air, a route can be established through rooms using open doors to cool the entire house without compromising the security of the house.
  • Place outward-blowing fans as high as possible, such as in a second story window. Since hotter air rises in the house, these higher fans will remove the warmer air first.
  • You can dramatically increase cooling performance temporarily (~1 hour) by draping and securing an ice-cold soaked wet towel across the inward-blowing fan. The air propelled by the fan will push past the towel, taking with it cold evaporating water. Size of the towel should match the size of the fan, so use discretion (a beach towel is probably way too big.) Also, be aware of potential water damage and electrical hazards; don't use this method if the water will drip onto the outlet or power cord connection.
  • A bathroom fan can be used as an outward blowing fan. They are often located on a ceiling maximizing the warm air rising effect.
  • Fans produce cooling in 3 ways:
    • By bringing cooler air in from the outside and pushing warmer air out of the house. This is the main focus of this article.
    • By pushing the warm, moist air near a person away and replacing it with cooler, dry air. Ceiling fans, for example, cool in this way.
    • By increasing the rate of evaporation of a liquid to produce evaporative cooling. To cool spaces, this method only works well in areas with low humidity, such as deserts. When cooling people, it works well when the people are wet or sweaty, such as when coming out of the shower/bath/pool, or after exercising strenuously.
  • If a house is not built to handle the electrical load of central air, window fans are less likely to overtax the electrical system, as they use less wattage, use it during off-peak hours, and distribute usage evenly throughout the home.
  • Fan maintenance:
    • Leaving fans on for substantial portions of the day will shorten their lives, especially if they are left in the window during rainstorms. Performing maintenance on them will extend their lives somewhat, however.
    • Don't operate a fan that isn't working properly, especially if the blades aren't moving at all or you detect a burning smell. Such a fan could pose a fire hazard.
    • The most common problem is a lack of lubrication. A sign of this is the blades rotating more slowly, especially at startup, than when new, and eventually not rotating at all, and making more noise. If this is the problem, unplug the fan, move it to a garage or other area where fumes won't be an issue, then lubricate the area around the fan blade assembly drive shaft. It may be necessary to remove the fan housing/safety grating, or even the fan blade assembly, to access this area, although a can of WD40 (or equivalent) with a spray tube may be able to reach the lubrication points more easily. Rotate the blades during and/or directly after the lubrication process to distribute the oil more evenly. Be careful to avoid spraying oil (or allowing drips) on the electronics, such as those around the power switch. Let the fan sit for a few days until the excess oil fumes evaporate. Use this fan to blow outwards initially so that any residual fumes are blown outside the house.
    • Another common problem is an electrical fault – typically a wire which has come loose from a solder point or other connection. If you feel confident with a soldering iron, you may be able to repair this yourself. The power switch is the most common area for this type of electrical fault. If necessary, you may also bypass the power switch, so that the fan comes on whenever plugged in. This will mean you will lose the ability to use multiple fan speeds, of course.
  • Fan cleaning:
    • Fans tend to get dirty during continuous operation, picking up dirt and dust from the air they circulate. This actually serves the function of cleaning the air, but is also unsightly. They will pick up grease if used near a kitchen and yellow smoke tar if used near smokers.
    • Unplug the fan to clean it, then use water, window cleaner, or diluted dish detergent on a paper towel. If using detergent, wipe it off afterwards with a damp paper towel. Again, you may need to remove the fan housing/safety grating to access the blades. Set fans cleaned with solvents or detergents to exhaust initially, so any fumes are blown outside the house.
    • Another option is to simply hide the unsightly fans in windows in less often used rooms, such as a utility room, while using new fans used in areas everyone will see.
  • If fan ventilation is not appropriate for your home, fans can still be aimed at people inside the home, with the windows closed, in order to cool the people directly. In this case, be sure to turn the fans off when everyone leaves the room, since fans produce heat without any corresponding cooling effect when nobody is in the room to benefit from the increased air circulation.
  • Removing fans from windows when not in use helps in maintaining the proper temperature, but might be difficult for the elderly or other individuals. In such cases, the fans can be left in the window. However, during rain storms, fans should be removed if at all possible to prevent water damage inside the home.
  • This cooling method can make it uncomfortably cool inside at night. Wear warm clothes and use a thick blanket in bed if this happens.
  • You may also use box fans that are also designed to be also used as window fans, such as the Lasko Weather Shield Box Fan, since it is also designed for the purpose.

Warnings

  • Avoid having fans too close to ground level. At night this will bring excess humidity into the home and could cause mold problems.
  • Avoid using fans around small children who might put their fingers in the fan blades. The gratings in the front and back of a fan are often spaced widely enough for a child's finger, a pencil, or other object to be inserted.
  • Don't leave fans in the window during rain showers, as water may come in through the window and damage the house. This is particularly a problem where fans are blowing inward. Roofs with large overhangs can help to reduce this problem, especially on the top floor, except when there are strong winds.
  • Don't use a malfunctioning fan. If the blades aren't rotating at the proper speed or you get a burning smell, disconnect the fan immediately. Otherwise you could get a fire which could spread to the drapes.
  • The window fan method may be hard on wooden furniture, as daily temp and humidity variations can cause cracks or warping.
  • Ensure fan cannot fall out of the window.
  • Be prepared to accept a 10-20 degree F temperature range from day to night inside if using this method, as window fans won't allow you to control the indoor temperature as closely as an air conditioning unit does.
  • Be careful with the electrical cord:
    • Don't pinch it with the window or have it hang across the floor where it could be a trip hazard. If necessary, use a properly rated extension cord so that it will lay flat on the floor, against the wall, to eliminate this Prevent People from Tripping over Cords, Wires and Cables.
    • Don't run cords under carpet, as this can allow heat to build up to combustion temperatures.

Things You'll Need

  • Window fans (the more the better, up to the total number of windows in the house). There are units specifically designed to be left in the window for the season, typically with two small fans, a method provided to secure them to a window, waterproofing, and baffling on the sides and masking around the fan to prevent local circulation. Many also provide the ability to reverse the fan direction without turning the fan around. Box fans may also be used in windows, and are often more powerful and easier to remove.
  • Extension cords rated at or above the wattage of the fans you are using (optional).
  • Inside and outside thermometers (optional).
  • Electrical outlet timers to turn fans on and off automatically at preset times (optional). Ensure that these timers are rated at or above the fan wattage. Note that using electrical timers requires leaving fans in the windows all day long, which decreases cooling efficiency. (Also, if using timers, set fans blowing inward to start slightly earlier and turn off slightly later than those blowing outward to prevent creating negative relative pressure inside the house.)

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