Fans, not just air conditioning, can help houses beat heat
YTim Carter
ou might be one of the tens of millions of people who suffered in the blistering heatwave that gripped much of the country in July. I happen to live in central New Hampshire, and it was a withering 91 degrees with a dew point near 70 degrees on a recent weekend. That's rare for this part of the nation, and I know it's much hotter in other locations.
Summer heat is nothing new. Not by a long shot. If you dig deep into weather history and connect it to homes and how our ancestors survived, you will discover that builders and homeowners learned how to cope with the heat and humidity.
You might wonder what's in play when the sun's powerful infrared rays strike your home's roof and windows.
I used my infrared camera recently and captured a frightening image of my roof. The south-facing roof shingles, which take a direct strike from the sun, heat up to almost 163 degrees. That's hot enough to cause second-degree skin burns in seconds if you touched the roof surface. Believe me, that's the voice of experience talking.
That heat is transferred to the wood framing that supports your roof. Years ago, I recorded temperatures in my attic of 140 degrees. The entire roof radiates heat much like a campfire that has reduced to glowing embers.
This heat is further transferred to the inside of your home because the ceiling below your attic starts to get very hot. Once again, think of how a campfire keeps you warm.
Perhaps you're wondering about your attic insulation and why it's not helping to keep you cool. The reason is simple: Insulation is a building product that slows the transfer of heat, but it does not stop it. To stop a large portion of heat transfer, you need a radiant barrier similar to aluminum foil.
Keep in mind, as the temperature of your attic starts to climb as the sun gets higher in the sky, so does the temperature of the insulation in your attic and walls.
The trouble is, the insulation then does the job it's supposed to do late in the day and early evening. You want your house to cool down, but it's slowing the transfer of heat from the inside of your house to the outdoors. It's a vicious circle of one of the laws of physics.
I remember growing up in the Midwest without central air conditioning. My mother had all sorts of electric fans we used in the bedrooms to blow lots of air across us to help make sleeping possible.
Fans help cool you because they increase the rate of evaporation of your body's perspiration. As the sweat turns into water vapor, it takes some of your body heat with it. The faster you can make this happen the cooler you will be — to a degree, of course.
Years ago, homes were built with large overhangs so the sun would not enter windows during the hottest part of the day. You don't see generous overhangs in new homes too often. This is an example of a building practice that is going from history to legend to myth.
Older homes had drapes over the windows indoors, and people would pull these closed during the day to stop the direct influx of infrared rays into the living space. Now, if you don't like drapes, you can coat windows with nearly invisible films to reduce the absorption of infrared into your home.
Whole-house fans have been kicked to the curb for the most part as central air conditioning seems to be the way to combat hot houses. Whole-house fans can do a marvelous job of cooling you down, though, because you can control where the breeze is in your home depending on what windows you open.
Tim Carter writes for the Tribune Content Agency. You can visit his website (www. askthebuilder.com) for videos and more information on home projects.