Whole house fan with conditioned attic?
Pete Dusenberry| Posted inMechanicalson
We’re building a house in the Northeast and the owner is insisting on a whole house fan in addition to central AC.
The attic will be a semi-conditioned space with foam insulation in the rafters. This means no outside air exchange.
Is there a way to put in a whole house fan and vent directly outside?
House is about 3000 sq ft.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
You can do it, but in the snowy northeast it's better to put the fan on a gable end, not the roof.
If you HAVE to go through the roof (or even if it's a wall), something insulated and reasonably air-tight like the Tamarack's TTi-HV3400 with the R38 automatic doors is probably your best bet on a house that size.
http://www.tamtech.com/HV3400-R38-Insulated-Ghost-Whole-House-Fan-Up-to-3400-sf_p_10.html
I haven't seen the installation manual on that unit- don't know for sure if a horizontal mounting would be disallowed, but I expect it should be OK in any orientation.
It sounds like you've warned the owner about the drawbacks and he wants to go ahead; there's still an opportunity to educate him about smart operation, in particular checking the dew point outside and only running it if the outdoor dewpoint is lower than say 55 F, or better, comparing to the indoor dewpoint and only running it if the outdoor dewpoint is lower than the indoor dewpoint. There are weather apps that can give you current and forecasted dewpoint, and there are consumer weather stations that can display dewpoint for a remote sensor.
I agree that a gable end mounting is what you want, and that Tamarack is likely the best source. I'd ask their advice about which unit could be mounted in that orientation.