It’s often recommended that window fans be used to draw cool air into dwellings at night, which in hot weather or heat domes may reduce the need for air conditioning.  This is good advice but there are other actions you can take to cool your living spaces more effectively that can further minimize the use of electricity.

1.  Window fan cooling at night: 

Turn on your window fans when the air outside is cooler than the thermometer reading inside your home.  You can use a fan to exhaust warmer air out of your home or to blow cool air in, depending on your needs. 

It’s often recommended to draw air into your home from the ‘cooler’ side of the dwelling.  While that advice is useful if the air outside is still, if the wind is blowing, cooling your home will be faster if your fan is blowing in or out with the wind rather than against it.  Opening windows and checking the direction of the air flow is the best way to know how to orient your window fans.  Weather reports and phone weather apps also report wind direction, but those report overall wind direction over a large area and may not be an accurate indication of how the air is flowing around your home.  Because local terrain and structures, and houses and apartment buildings, create wind eddies, the local air flow at your home could be different or even the opposite of the reported wind direction. 

Turn off your fan in the morning when the outside temperature exceeds the indoor air temperature of your home.  A couple of inexpensive indoor air thermometers will give you a good estimate of indoor air temperatures. If you can, remove the fan and close the window, or otherwise block hotter outside air from entering your home through the fan. 

Cool the object in your home, not just the air:  Your home will stay cooler for longer if you open closet doors, kitchen cabinets, dresser drawers and other enclosed spaces overnight.  The goal is to use the outside night air to cool the objects in your home, not just the indoor air, and cooling the objects (furniture, cabinet contents, etc.) will occur faster if cool air can circulate around them.  In the morning when the air outside becomes warmer than the inside, close closet doors, cabinets, etc. to slow down the rate of warming during the day.  It will be as if you have multiple cooler chests in your home that will help keep it more comfortable inside for longer during the day.

Using fans may not be practical if you are concerned about leaving a window open at night after you’ve gone to bed.  Also, window fans may let in street noise, light, and perfume odors from nearby clothes dryer vents, or other pollutants. 

If you have a two-story home or one-story with a basement, try using fans in the windows of the upper floor to blow indoor air out and opening the windows on the lower floor to let cooler air flow in (or having fans on lower floor windows blow into the home). By creating a ‘chimney effect‘ – when warmer air can move from the lower to the upper floor – you may get better overall cooling than if fans on both floors blow in the same direction.

Of course you can use box fans or ceiling fans inside your home to circulate indoor air, which may help keep your body cooler.  Having a box fan on the floor blow air through a wet cloth also will help cool indoor air in sleeping areas (but will increase humidity). 

2.  Window curtains and blinds:

Blocking the intense radiant energy of the sun from entering your home during warm weather is important.  I angle my Venetian blinds to block out the sun wherever it shines through my windows and then open them to let in the indirect light when the window is in shade.  Sun-blocking window drapes also can be helpful, as can putting automobile windshield sunscreens in windows when in direct sunlight.  If you are able to put up outdoor window awnings or other outdoor shades, that also will help keep intense rays from the sun out of your home.  Patio awnings and other man-made sun-blocking features, such as pergolas, also will keep your local environment, and therefore your home, cooler. 

3.  Blocking other heat and smoke entry into your home:

If you have a clothes dryer in your home, you may be surprised at how much hot outside air can get into your home through dryer vents; the same is true for stove vents.  In very hot weather, or when the outside air is unhealthy because of wildfire smoke, gasoline-powered lawn mower or leaf blower fumes, pollen, or other pollution, stopping entry of outside air into your home is important.  I have found that plugging the dryer vent with bubble wrap and sealing it with easily removed masking tape, and blocking the stove vent by enclosing the filter in a plastic bag, helps keep noxious outside air out of my apartment.  I have access to an outside umbrella clothesline, so it’s possible for me not to use my electric clothes dryer at all for 8 months of the year – at least when it’s not raining. 

4. Create or preserve outdoor vegetation that provides shade: 

Trees and shrubbery that shade your home not only block the radiant energy from the sun from reaching the walls and roof of your home, but they also cool the air by releasing water vapor in a process called transpiration.  Several studies have shown that passive cooling from shade trees and other vegetation can reduce the temperature next to your home by 5-10 degrees (F), and that neighborhoods that have more trees and less asphalt are many degrees cooler than those with tree shade ‘deserts.’  Planting new shade trees or managing existing trees and shrubs to provide shade for your yard and dwelling not only will keep your home cooler but in the process will remove heat-trapping carbon dioxide from the air – all without using electricity.  Outdoor vegetation and shade near the windows also will further cool the night air via transpiration as you draw it into your home. 

I hope these low-energy and passive cooling techniques help you stay cooler in the summer and reduce your electrical bills! 

Please let me know if have other ideas for staying cool while minimizing electricity and air conditioner use at home.