3 ingredients for comfortable indoor temps
The plus is that they work for free, using the sun's rays. The minus is they work only when the sun shines. If a cloud drifts by, blocking the sun, the fan stops. Worse, as the sun moves through the sky, contact with the solar panel is lost and the fan stops. At best you'll get part-time cooling.
The hardwired version is thermostatically controlled to kick on when the attic reaches a certain temperature. True, they do use electricity from the grid, but usage is minimal. The bottom line is that you'll exhaust hot air when you need to regardless of the vagaries of sun and cloud movement.
Beefed-up insulation, vents and an attic fan could well be all you need. But if you want to go for the whole megillah, consider a whole-house fan.
Attic fans move hot air from the attic only. They do nothing to promote air exchange inside the house. A whole-house fan pushes hot air from inside while drawing in cooler air inside through open doors and windows. Placing a whole-house fan at or near the high point of the house will accelerate the removal of hot air to the attic while replacing it with cooler air from outside.
But a whole-house fan will not make the temperature lower than that of the outside air. Run a whole-house fan only when the temperature outside is lower than the house's inside temperature. Nights and early morning are the best times.
Some planning is required to choose a whole-house fan. You'll need to size the fan to work efficiently. Unless you're an accomplished carpenter, you may need help with installation. Also count on using an electrician to properly wire the fan. If a permit is required, get one.
Once more, though, your first line of defense against the heat is insulation and proper venting. Start from there, see how it works and if it's not good enough, check into the fans.
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