Originally Posted by bennelson
The way I see it, it's all about "Delta-T", that is, the DIFFERENCE in temperature.
The bigger the difference on one side of the wall than the other, the more heat tries to push through to the other side to even out the temperature.
Insulation slows down this process, which is why we insulate our houses, to keep warmer longer in the winter, and cooler in the summer.
I recently put the remote reading sensor from my wireless indoor/outdoor thermometer in the attic of my house. It's been hot lately, and we've been running the air conditioning, set to 80 degrees F.
In the attic in the middle of the afternoon, it's been 120-125 degrees. So, that's a 40-45 degree difference than in the house. If it were winter, we might have the furnace set to 70 and the outside temperature might be 25 or 30. That's that SAME 40-45 degree difference!
Basically, the AC is working as hard in the summer, as the furnace is in the winter when it's below freezing! Imagine if you had a way to warm up the outside in the winter - your furnace would have to run that much less because of it.
That's kind of what you are doing if you can cool your attic. If you can drop the temperature there, it's that much less heat trying to beat its way into your house!
Anything you can do to reduce the Delta-T (including raising the thermostat in the summer) reduces how much energy is used to heat and cool the house. It just seems like a good attic fan is a simple, cheap, way of doing that.
(The summer/winter comparason isn't perfect. In the winter, heat loss is sort of everywhere - walls, attic, foundation, etc. In the summer, the attic is the hottest thing, but you also have to consider solar gain, and that the walls of the house are unevenly heated as well)
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