Quote:
Originally Posted by bakon
Some say they pull air from inside house, but with such low CFM, and all the soffit vents that’s not a concern. But pulling from the ridge vent in, well that would be counterproductive, possibly harmful. Cost at about $2k for two large ones from Solar Guys installed, I misspoke if I say cost for reverse airflow would not be a problem.
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In theory the fans (solar or 120v) pull air in from all sources (ridge, Soffit, and a/c cooled home via leaks) equally, this theory doesn't consider friction. In other words the fans pull air predominantly from the closest source as that air moves easily to the fan.
I've already illustrated that there is no HVAC savings to justify solar fans there are two other aspects that are worthy of discussion. Will your attic be cooler and will your roof last longer?
More ventilation would lower attic temp and this extend shingle life but only if there is enough of it. I can go though the math of it but frankly it's more effort than I'm willing to spend here. Suffice to say two fans aren't enough to make a measurable difference.
But additional static vents could make a difference as they are so inexpensive that you can put six to ten more on a designer home with ridge vents and effectively double your roof peak ventilation.
That's exactly what I did.