"Edwin Pawlowski" wrote in message
t...

"DonC" wrote in message
But we're talking about a different animal here. A WH fan "moves"
existing cool air supplementing AC at a much, much cheaper cost.


I hope you mean instead of AC, not supplementing. You don't run both at
the same time do you?

As for the flat roof, how much space do you have up there above the
joists? How much venting? It may be possible, but you may be better off
looking at the mushroom cap type of roof ventilator.


I guess I wasn't very clear on that. By supplementing I meant using cool
air during the night and early morning so as to delay turning the AC on --
if turning it on at all. If the wind is blowing the fan isn't really needed.
But that's not usually the case. The fan just gets things moving.

There's 2x12s so I guess that's 11 1/2" +/-. I'm not sure a typical
ventilator pulls enough CFM. A typical WH fan is rated 3000 to 4000 CFM.

An example of the economies of a WH fan using Atlanta as an example (The
savings would be much greater here -- south of Tucson):

.. Operating a properly sized 2-ton air
conditioner with a seasonal energy
efficiency ratio (SEER) of 10 in Atlanta,
Georgia, costs over $250 per cooling
season (1,250 hours), based on
8.5¢/kWh, or roughly 20¢ per hour
of runtime.

.. By contrast, a whole house fan has a
motor in the 1/4 to 1/2
hp range, uses 120
to 600 watts, and costs around 1¢ to 5¢
per hour of use.