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All-Day Fan Cooling

July 13th, 2016
cooling, fan  [html]
When it's 90F in the middle of the day, you're going to be hot even with a fan. But by taking advantage of the day/night temperature difference, you can keep your house pretty cool without AC.

During the summer in Boston we'll typically have nights that get down to 70F with days that get up to 90F. If you also have >15F between your lows and your highs you can use this difference to do a lot of work! Here's how:

  1. Run as much air through the house as possible overnight. Open windows, put fans in them, maybe get a whole-house fan. You're not just trying to cool the air in your house, you're trying to cool anything that can hold heat.

  2. In the morning, turn off the fans and close the windows. Now that your house is cooler than the outside you don't want to let in that hot air.

  3. Additionally, draw the curtains. Sun shining through the windows does a lot to heat your house. The more light your curtains block the better for keeping cool.

Our thermostat is in the center of the house, and the extremes feel like they vary more, but typically it will read 70F when I leave the house around 7am, and 75F when I get home around 6pm, despite an 85-90F high. It's much better than what we used to do, keeping the curtains and windows open all summer. Additionally, it's much cheaper than AC, and the air isn't uncomfortably dry.

One thing people can miss with leaving the windows closed is the feeling of a cooling breeze. Which makes sense: we're lowering the temperature in the house, but with the still air our skin is missing the chance to cool evaporatively. To fix this, set up some fans inside to get the air moving. I like ceiling fans because they stay out of the way and have no setup time, but any sort of fan that can blow at you works.

Caveat: this only works if your house has good insulation. But if it's not well insulated, fixing that would probably pay for itself by lowering your heating bills.

(When everyone spent the day elsewhere this didn't matter much, just slightly warmer nights, but now there are now seven people [1] home during the day here so it's important that the house be livable.)


[1] Julia works from home, Lily and Anna are home with a nanny, and my sister and her husband are home with their newborn.

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