Good points I had not considered with my attic situation. I do have ridge vents and two roof vents. As with some others, I always crack my attic door, which is in the garage, and then turn on a fan sitting in the garage aimed at the attic door. Temperature will drop to about 5 degrees above ambient temperature in about two hours. Now, I only fire this "system" up when I get home around 1700. I have a programmable thermostat in the house the cranks down to 73 degrees around 1600. I know it makes a difference come early evening when the house reached 73 degrees, say around 1830 or so. But, one day I was home and it was hot as all get out, opened the attic door and did the same thing as I always do in the evenings, but it really didn't make a difference. Temperature stayed about 115 up until the sun was not directly overhead. I've always wondered how much thermodynamics played into this. Once the attic reaches it's highest point and the whole attic is a heat sink, does dropping the air temperature really drop the temperatures of the substrate that much? Heat always travels from hot to cold. I got a boat load of insulation up there also. But heat transfers easily. It's funny. In the mornings I check the temperature. It will be a lot cooler than the ambient temperature up until about 1000, about the time the sun starts hitting the shingles directly overhead so I know the ventilation up there is pretty good. Hence, my dilema on putting an attic fan up there.
