Do you simply want to evacuate warm air or do you also want to feel air
movement? In the former case, just
compare the CFM of proposed with the two current to know how much air they
move, then figure volume of your house to determine length of time for an
air exchange. I imagine the whole house fan will win hands down.
But CFM isn't the only factor for a breeze...much depends on where the air
comes from, where it goes and what obstructions there may be. Size of
intake opening matters too...the larger the opening the less fan generated
breeze through it.
You say you have one fan blowing east, the other blowing west but where are
they relative to each other along a N-S line? And where is the bedroom
relative to them?
To give you an example, years ago when I was in college I had a long, narrow
apartment with a passageway between rooms like this...
Windows were on the north in kitchen, east & south in living room and east
in others. Closing all windows except one would result in a nice breeze
through that window.
I could just open my bedroom window and get great air flow, but if I keep the
kitchen door open it cools the thermal mass (concrete floor and ceramic tile) in
their which helps moderate the temp during the day and it also helps cool what
it can in the living room
The quiet ones tend to be belt driven, at lower rpm.
You usually have to insulate and seal it for winter.
I got around that building an upper box and door.
The one I have and the old one were too noisy. I don't like to run it,
maybe for a few minutes. I have been known to turn it on high, and get my
stihl gas blower, and dust the house out. I still want to instal a lower
If your satisfied with what you have, don't do it.
I found the whole house fan does a much better job of getting outside
air in and the air freshens the house. If you are the kind to worry
about heat loss in the winter they can let a lot of warm air into the
attic if you don't cover them during the winter season. Moving air
around can be noisy or it can be done quietly. Blade size, air speed
etc. and they bring in pollen, something to consider if someone has
allergies. All in all I like my whole house fan and I use a lot.
On 8/28/2011 11:39 PM, Malcom "Mal" Reynolds wrote:
I had a whole house fan (36") for about 15 years in a previous house and
liked it very much.
There are a number of gotchas of course:
1. If the nights are *not* cool then you are just moving hot air but if
they are cool then you can cool your house off in 10 minutes or so in
the evening. They are not of much use during the hot daylight hours. If
your climate is damp and/or pollen prone whole house AC may be a better
2. If you decide to go the whole house fan route get a belt driven
model. Eventually the motor will go and just replacing the motor is
easier and cheaper than replacing the entire unit. Get one that has a
motor rated for a rheostat for a wide range of speed adjustment as they
can be noisy at high speed and mostly useless at low speed. Every house
3. Build an insulated hinged box (that is easy to get to) to cover it in
cold weather as it will leak heat like you wouldn't believe.
4. Attic ventilation is key and should be based on the house square
footage not the fan's CFM. Its been probably 30 years since I researched
this so don't take my word for it but ventilation area needs to be
really large, something like 1/4 or 1/3 the square footage of the house.
I ended up ventilating about 1/2 of both gable ends. That is a *lot* of
cutting and vents so do take the cost, bother and view from the street
of this retrofit into the equation. Try to space the vents as equally as
possible on either end of the house to cool the entire attic rather than
just one end. One hot end of the attic will definitely be felt
downstairs. I didn't have a ridge vent as they weren't common then (at
least in SW PA). I am not so sure that they would be a good thing as
attic insulation would tend to cool off slower using radiation rather
than air blowing across it.
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