Thread: Solar powered air vent

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I don't see a problem with it. But then that is the first solar powered attic power vent I have seen. I might make note of it and tell my client that this is an unconventional design and unconventional designs tend to perform in unconventional ways.

Also write up that operating an attic exhaust fan will depressurize the attic, which in turn will depressurize the house, which in turn draws in un-conditioned outdoor air to replace the conditioned air which was drawn out, which brings in excess moisture - which must be removed by the a/c running longer.

Making the probable net effect of operating an attic exhaust fan a net negative, i.e., net energy loss, even though 'the fan' "costs nothing to operate" because it is solar powered.

My experience is that the solar powered fans operate at a much lower air exchange rate than the ac gable or roof fans. The are very quiet and effective in venting the attic. Jerry has a point, but a cooler attic is going to result in a cooler house. It would be interesting to see a real study that analyzes the trade offs.

Originally Posted by John Stephenson

Also write up that operating an attic exhaust fan will depressurize the attic, which in turn will depressurize the house, which in turn draws in un-conditioned outdoor air to replace the conditioned air which was drawn out, which brings in excess moisture - which must be removed by the a/c running longer.


Well I never thought of that...is that true to all power fans? Do you have "data" to support your conclusion?

Dr. Joe L.

He explained it in one of his classes I attended.

and who is Dr Joe L?
Blasphemy!

Originally Posted by David Banks

and who is Dr Joe L?
Blasphemy!

Building Science Corporation

Keep in mind that some folks agree with his opinions and others do not.

In a conventional attic with conventional asphalt fiberglass shingles on the roof in the Southern or Western part of the country, I can't see not having ventilation in the attic to relieve the heat that builds up during the day.

Originally Posted by Scott Patterson

In a conventional attic with conventional asphalt fiberglass shingles on the roof in the Southern or Western part of the country, I can't see not having ventilation in the attic to relieve the heat that builds up during the day.

In my house down in South Florida, with a conventional attic, I installed an attic exhaust fan like the one in that photo (except not solar powered), then, a few years later attended a few of his classes, went back and disconnected it.

I believe that the house was much more comfortable feeling with that exhaust fan not operating than it was with it operating - the house was a 1974 house, on the beginning of the tighter and better insulated upward curve of building construction, and there was enough air leaks and loss from the house into the attic to make a difference, and standard non-energy efficient windows, which allowed outdoor air in to make up for that air lost to the attic. In South Florida, that make up air was very humid air.

I think one key to remember on attic ventilation is that in order for it to work effectively there must be an inlet (soffit) and an outlet (roof) and they must be balanced.
Too much roof vent in relation to the soffit vent and the attic will be mildly depressurized even without a powered exhaust vent fan if on a sloped roof application.
Conversely, IMO if there is enough soffit vent even with a powered exhaust fan there would be little depressurization.
I can agree with Dr. Joe when we are talking new construction and unvented attics, but existing construction that was planned to have attic ventilation needs ventilation.
I am NOT a proponent of powered attic vents, but if you use them, then provide enough inlet vents to avoid depressurizing the attic.
I would recommend anyone to attend one of his classes if you ever get the chance, he is a very knowledgeable guy and entertaining to boot.

I cannot think of any other person who has had me in a room for 16 hours (two seminars) and I didn't want to run away. The only thing I've ever heard him say that I didn't like was that all houses in our climate should have white concrete tile roofs. I agreed with his logic, I just am not a fan of how they look and I dread the day when the big one hits and all these millions of two pounds missles are flying everywhere.

Originally Posted by Thom Walker

I dread the day when the big one hits and all these millions of two pounds missles are flying everywhere.

That's where wind borne debris (impact) protection for windows comes into play.