N. Thornton wrote:
wrote in message ...


I like Grainger's $73 4TM66
3-speed 16" reversible window fan with thermostat, which moves 5850 cfm
with 90 watts on the highest speed.


thats way cheap. I've been looking at 9"/12"ers at £100, about 150usd,
and 550cfm.

But more importantly most fans dont seem to have dB ratings, and that
is a real issue considering the fans would be above bedrooms and run
at night, and mounted on a springy PB ceiling.


Our current whole house fan is in the hall ceiling just outside the
bedroom, and we often run it on low speed at night on a timer, set to
turn off around 2am or so. The noise is kind of a low frequency
rumble that is not very loud, and does not keep anyone awake. But, I
suppose this could vary from brand to brand.

The fan is a 30 inches in diameter, and is belt driven through a step
down pulley -- not sure what the final rpm is, but you can see the
individual blades turning on low speed. If you are concerned about
the noise, I would be sure to get one with two (or more) speeds.
I think the price was about $150ish.

Some of the WHFs are fairly awesome on the highest speed -- the one we
had in our last house would pull the drapes in at a 30 deg angle on
several windows :-) -- good for a quick cool down.


Doing that well may require 2 fans, one to move outdoor air through the
house and another ceiling fan to mix it around in the house. The outdoor
air won't cool much mass if it just passes through the house in a compact
stream. It's also nice to have moving vs stillish air near the mass
in order to raise the surface airfilm conductance.




Thats my #1 concern here. A WHF will move air through the already
coolest parts of the house, but not through the rooms where cooling is
needed most. Not sure how to address that. Would still be a benefit
though, and much less cost than multiple fans.

You can control which rooms gets cooled by just opening windows in the
rooms you want cooled. To get the flow balanced the way you want it
between the different rooms, you may have to close the windows in some
of the rooms part way (usually the rooms closest to the fan). Overall
we find it to be a pretty flexible system. Although, if you have a
good place to locate a high capacity window exhaust fan, I don't see
why that shouldn't do the same thing. I think that a good window fan
location would be one that can pull air through other open windows
throughout the house, and in a location where you don't mind a fairly
high velocity of exiting air.

Don't overlook the fact that if you use a WHF, you will have to
provide an exit vent in the attic. Normal attic venting does not
provide enough area.

Regards, NT