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Originally Posted by Maker
What issue are you trying to solve?
What factual data do you have to document that there is a problem?
Can any of the attic fan sellers provide you with a written guarantee for performance, temperature reduction, and cost savings?
Would spending the money on better insulation be a better choice?
Would spending the money on more efficient AC hardware be a better choice?
Have you asked your energy supplier to conduct a free energy audit? See if they have a thermal imaging camera to look for insulation and window problems.
Are the existing soffit vent openings clear or blocked with insulation? Are there more than enough vents? Are baffles in place?
Why did they say "two fans"? Why not one, or three, or four? How did they come up with that?
You can put a remote temperature sensor in your attic and see what the actual temperature is. Maybe your attic is not as hot as you think.
Outside air moves via convection from your eaves to exit the vents at the top of the roof. Adding a powered fan often changes that. Air gets drawn into the existing vents by the fan. Natural convection is reduced, and the entire attic remains about the same temperature. This will always happen when the fan is placed anywhere near existing vents. The airflow becomes into the peak vents, and then out the fan. There is no airflow into the attic from the soffits. The attic air space below that fan height is stagnant, and hotter. Exactly opposite from expected.
The only fan I have ever witnessed being somewhat minimally effective was in a 2 story house, on the ceiling at the top of the stairs. They would open windows and turn it on after the outside temperature dropped below the inside temperature. That cooled off the living space and brought in fresh air. Effective only at certain times of the year; when weather conditions were right (low humidity); and when timing worked out (not hours after coming home to a hot house).
He was a geek and wondered if he could cool the attic space. Collected loads of temperature readings. When running it all day to see if it cooled the attic on a sunny day, or lowered the interior temperatures, those numbers showed no detectable change between running or not, comparing similar days. That was a different use case though... pressurization of the attic space, vs putting it into a net vacuum.
That unit had insulated metal fireproof baffles that closed when it was off. It also was not quiet. Because of the limited usage, he said he would not have put it in if he were able to go back in time.
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I agree. Use non-powered ridge vents and soffit vents with baffles that actually work. (Are there any here?) As hot attic air rises, if it has a way out, it will go out, and cooler (relatively) air will take its place.
As for paying $600 for a fan to suck air from your hot garage into your attic, remember that the air pulled in from outside May still be 90°, so you may not notice a difference. I didn’t. Waste of money, even though beautifully installed.
The reflective bubble wrap stapled to joists just below the roof turns out not to work very well. This was established by Fine Homebuilding magazine over thirty years ago, but people keep buying it because it’s not illegal to sell it. It just doesn’t work.
Insulation in Villages housing is the minimum allowed by code, and it is often trampled down by people wiring things in the attic. Blowing in another foot of insulation would cut electric usage a lot. If you are paying $250 a month for electricity in a 1600 sq ft house, it is probably a good idea, with a payback of several years. But my electricity bill runs under $100 a month, so the payback for me might be more like twenty years.