I once saw a top-ten list of inventions that engineers selected as the greatest scientific achievements of the 20th century. I guess it’s not surprising that air conditioning was among the list. After all, just fifty years ago few people had a/c units and suffered through brutal heat waves with only fans and open windows. So it is understandable for us to crank up the air when summer comes. The problem is that people often use it much more than it is actually needed. Many homes in the northern half of the U.S. use air conditioning for at least three or four months straight, when it might only be necessary to use it half that much. The question is: How do you stay cool without air conditioning?
As air conditioning has become more prevalent in the last few decades, people seem to have either forgotten or completely missed the practical value of window fans. A relatively inexpensive window fan (with quality units normally costing between $30 and $40) can eliminate the need for any air conditioning on many nights and even some days, and generally cost a penny or less per hour to operate. They can also keep you more comfortable while you sleep by supplying a steady stream of cooler air from the outside, whereas central air units are off much of the time overnight which can make your living space feel stuffy. The continuous movement of air that window fans provide enhances the cooling effect on the body.
Generally speaking, nights will get the coolest when skies are clear and humidity is low. A dry air mass which warms to the mid-to-upper 80s by day will likely cool into the comfortable 60s at night, but winds usually die down in the evening which makes window fans essential for getting that cool air indoors. In fact, they can often make your living space cooler overnight than if you had left the a/c on with the windows closed. Two or three strategically-placed units can provide a surprising amount of low-cost comfort, and they are very lightweight and easy to move around as the weather dictates. When it is uncomfortably warm and humid, turn on your a/c and be thankful you have it. But give your wallet a break and take advantage of the many nights where the temperature drops well down into your comfort zone.
If the forecast low temperature is less than 70º F and the humidity feels comfortable to you, then you will likely sleep better and keep your house cooler overnight by using window fans. If the next day is not very warm, the cool air “buffer” that the fans provide at night is sometimes even enough to keep you comfortable during the day without any need for air conditioning. However, you do NOT want to keep fans blowing warm outdoor air into your home all day. Just close all the windows when you get up in the morning to help conserve the cool air as long as possible. Then if your home warms to your comfort limit during the day, turn on the air conditioner as needed. If you go to work or school all day, use a programmable thermostat (starting around $30) to have the a/c turn on an hour or two before you return so that you are not cooling an empty home unnecessarily.
For years I have heard the claim that you should not turn the air conditioning off for any period of time because the system will have to work harder when you turn it back on. Under certain conditions this may be true. However, if you normally keep your thermostat set at 74ºF but instead you use window fans to flood your home with cool 65ºF air overnight, which do you think will get your house cooler for less money? The next afternoon, if the house warms to your comfort threshold and you decide to put the a/c on, then you will have lost no comfort and will have likely saved quite a bit of money in the process.
Get in the habit of checking out the forecast overnight lows for where you live to judge whether you can benefit from putting window fans in place. Just keep in mind that low temperatures in the suburbs will likely be a couple degrees cooler than the official forecast low. With a little knowledge, planning and experience, you can use weather forecasts and daily trends to anticipate when you will be able to skip using the a/c and opt for window fans as your main cooling engine. Spend some extra money to get a better brand or model that will last you for many years. Late summer (before Labor Day) is a good time to buy a new fan because retailers start to discount them to make room for fall merchandise. Just be warned that some retailers sell very cheaply made units that are noisier and less durable. Shop around a bit before you commit to a purchase.
Although seasonal allergies, ambient noise or home safety may be among the potential issues in using window fans, their purchase price can easily pay for itself in energy savings in less than one season when you take advantage of cooler summer temperatures. If you become adaptable to our region’s summer weather patterns, you will find that Mother Nature offers up a surprising amount of cool air in-between her spells of hot, nasty weather. So take your air conditioner off auto-pilot whenever the weather allows, and start saving big on your summer electric bill.
Paul Hanley is a long-time Cherry Hill resident and Environmental Science professor at the Community College of Philadelphia. Look here on Sustainable Cherry Hill for more upcoming blogs from Paul in the coming weeks. He can be contacted at phanley [at] ccp [dot] edu.