on 10/7/2007 12:47 AM DonC said the following:
"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.


I have a whole house fan and CA, and we use the fan for a number of
reasons other than getting cool night air in the house. Did you ever
burn something in the kitchen and the whole house smells or fills with
smoke? The fan will clean out the smell and smoke in a short time.
I let the dog (large Golden Retriever) out one night and she came back
in after having an encounter with a skunk. This was 12 AM at night and
we spent the next hour washing her in the tub with tomato sauce, tomato
soup, ketchup, or anything else we could find with tomatoes in it. The
fan cleaned 'most' of the smell out.
In the case of having an accessible attic. In the summer, when the attic
is about 130º F (I have a black roof with no rafter insulation, but
soffit and gable vents), I turn the fan on and blow the hot air out of
the attic before going up there, and leave it on while I'm up there. It
saves getting drenched with sweat and having to take another shower.


..--

Bill
In Hamptonburgh, NY
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