Most of the time I caution people away from attic fans and then I give them a copy of 4lorn1’s well written and humorous take on the “benefits†of an attic fan.
Here’s the old link in case anyone cares to read it:
From: DerfGreen Jul-23 11:10 pm
To: ALL (1 of 7)
60964.1
However one aspect of this thread that wasn’t addressed was the question of retrofit HVAC in the attic. If you have a retrofit in your attic would the fan help the AC unit run more efficiently?
Dan
Replies
Having an attic fan, I'm interested.....but I can't seem to make out the link. Could you repost the link?
Thanks
Mike D
Doh! Finally figured out how to plug in the link number.
Pretty good thread - thanks.
Mike D
Edited 6/29/2007 9:02 pm ET by Mike_D
"he exhaust fan in the attic can literally suck the conditioned air out from inside the house. A double whammy because not only are you blowing out air you paid to cool but this causes the inside of the house to draw uncondioned air from outside the building envelope. Your literally pumping in hot air."
Except change it from sucking conditioned air out of the house to sucking conditioned air out of the house and the leaks in the duct work.
You should make sure that the all of the connections are sealed and verify with duct pressure tests.
Likewise insulate all of the ducts and what you can of the airhandler.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
So, if everything is super- insulated and taped off, the heat level in the attic doesn’t affect the air handler in the attic? Is that basically the bottom line?Dan
Your point is one I have pondered myself. Several years ago I installed a Unico AC system (high velocity). I put the airhandler in the attic, which means all my ducts and return are there also. I actually have a flat roof with a "crawl space" of about 28" on the high end of the pitch and 8" on the low (roof and ceiling joists actually overlap each other). It gets plenty hot up there and I wondered if I was "taxing the system" with that additional heat. I looked into attic fans and found some solar operated ones on line, but with a flat roof I have to mount the fan on a curb, which one web site mentioned causes the "Venturi (sp) effect" -- and I am still trying to figure out what that is. If you made sure you had adequate intake vents to replace the air the fan takes out, and that all your AC ducts are properly sealed, I don't know how it could hurt to have a fan. Of course, does the cost of running an electric fan exceed any savings on the AC. Is a solar fan powerful enough to move the necessary amount of air. Are the intake vents properly sized and placed in relation to the exhaust fan. And what about that Venturi effect? hmmm Is there a NASA engineer in the house? I gotta go lay down.
Yes..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
You're talking an attic ventillation fan, not a whole house fan, right?
The only advantage I can see would be for those (somewhat idiotic) cases where the condenser unit is in the attic. The AC fan motor will be cooled by house air.
The only things that might suffer from the heat would be fan control circuitry (of which there's little in a conventional split AC unit) or dampers and associated zoning controls.
Of course, any time ductwork is outside of conditioned space it should be tightly sealed and well insulated.