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Treebeard's Stumper Answer
3 Oct 97

Fall is a changeable time. Last week it rained, but it's been hot this week. The max/min thermometer on the science building porch recorded a high of 105 degrees in the shade over the weekend! We've been running our fans at school and at home trying to beat the heat, so here's a practical stumper about fans. What's the best way to place a fan by an open window for maximum cooling effect? Should the fan blow into the room from the outside, or should it blow out the window towards the outside? Why?

What's the best way to place a fan by a window? The kids at school agreed 6 to 1 that a fan should blow out, at least when it's hotter inside. I usually wait until afternoon to turn on my fan, and point it to pull the hot air out so cooler air will replace it. This is also how computer fans work. But I'm still not convinced. During the day, I sometimes turn the fan around just to make a breeze. The fan only moves the air, but it makes the air more cooling by increasing the evaporation of perspiration from our skin. It's complicated!

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Marc Kummel / mkummel@rain.org