" wrote in
:

On Thursday, July 25, 2013 5:04:53 PM UTC-4, Ed Pawlowski wrote:
On Thu, 25 Jul 2013 12:10:50 +0000 (UTC), DerbyDad03

wrote:









It's not like you can go buy a fan that lists "doesn't suck outside
air

into the house" on the spec sheet.





Sure you can. Any fan, in fact, can be made to do that. All you need

is a gable vent at each end of the attic. Air comes in one end, goes

out the other. No air enters the living space. Cools the attic.


Now I have to disagree. DD has a point. Even with a gable vent in
each end of the attic, you can't guarantee that no air is going to
come from the conditioned space of the house. I'm assuming you mean
that you put the fan in one gable and use the other to supply the
incoming air. That fan lowers the pressure in the attic. The air
will then come into the attic from any and all available routes. Most
of it will likely be from the other gable vent. But some can be from
leaks from the conditioned living space, eg around recessed ceiling
lights, around switch plates, bathroom fan openings, etc. That is one
of the big arguments against power venting an attic. And the effect
depends on the CFM of the fan, the available intake openings, etc.

Yes, some measure will enter from the conditioned living space. How much?
Well, the path of least resistance like water and electricity. If the
venting of the attic sucks like having one gable vent, undersize soffit
venting, blocked soffit venting and the like, the attic fan is gonna suck
more conditiond air from the house as it becomes a lesser path of
resistance.

And keep in mind someone decides to put an attic fan in a gable vent and
has ridge venting, path of least resistance === in the ridge vent and
out the gable fan.