I have a 1700 sq. foot house without A/C, I installed (2)whirly-bird
ventilators last year, I counted 12 -- 4 X16 soffit vents. My house
has many ceiling fans but it does warm up in the afternoon if the
outside temp. reaches 80F and above, my attic temp. reaches about
110-120F on those warm/hot days. Would a power attic fan (roof
mounted) be better or a whole house fan work with my current vents??
Home is in Southern California, warm 80F-90F days and 65-75F nights....
I would say you are doing well. I would not go to a power roof fan.
If you like and you are not using central air, I would consider a whole
house fan mounting in the ceiling into the attic. It not only will help
reduce the temperature in the attic, but it will bring fresh (hopefully
cooler) air into your home.
Ideal is both.
If you have no AC, go with the whole house fan. The advantage is that it
will draw in cooler air from outside and push the hot air out of the attic.
The disadvantage is that on a very hot day, it will draw in the hot outside
air and replace what may be cooler inside. That is when the power vent in
the attic is best.
If you do add AC, you don't want to use a while house fan at the same time.
Ditto that, but using the fan for double-duty. In my case, during the
day the power vent fan in the attic switches on around 100 deg. F, with
the attic sealed off from below. When temps drop outside in the
evening, I open some windows at the (N) side of the house, farthest
from the door to the attic, and open that door, then drop the setting
on the fan t-stat. Soon, I'll just put in a manual switch in parallel
with the t-stat, or a timer.
Starting a power vent fan in the attic when it's only 100 degrees is a
waste. Attic insulation should be more than adequate to handle a 25
degree temp delta. What yo need the attic fan for is to keep it from
getting to 140. I have mine set to go on at about 110
When temps drop outside in the
FWIW, I have mine set to go on at 90, and I don't think that's a waste;
it can't keep up, so needs a head start -- any higher and the peak attic
temp gets too high. So the devil, as always, is in the details. If you
have a relatively small fan, as I do, having it come on early might make
a lot of sense.
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On 20 Jun 2006 16:35:10 -0700, firstname.lastname@example.org wrote:
I'm one of the few people here who loves his roof fan, and has no
desire for a whole house fan. Use google to search on
fan roof and words like that, and my from- address in the headers
here to find long posts about my views, for what they are worth.
Comparing the two, roof fans work during the day to keep the attic
from getting much hotter than the outside air. I'm guessing on most
days it gets no more than 10 degrees hotter than outside, but I really
should check sometime. Mine starts about 10 in the morning and turns
off between 6 and 10 at night depending on how hot and sunny it is.
It's always off by the time I want to go to sleep, so it's quiet then,
but it's only a small noise even when it is running.
They work just as well with AC as without, because the cooler attic
transmits less heat to the second floor than a hot attic does.
Whole house fans work when it is cool out, or at least cooler out than
it is in. If all you have is the whole house fan, during the day,
the attic will get as hot as it does now, and will transmit as much
heat to the floor below as it does now. (And if you store anything in
the attic, it will be exposed to temperatures as high as 130 or 140
for hours during the day) If you or someone in the family comes home
early, and on weekends, and even some days when you come home at 5:30,
it will be too hot outside to turn on the whole house fan. Some times
it doesn't cool off outside until 10 or 11, iirc. It will also bring
in, with the fresh air, all the humidity that is outside**. It will
also bring in the dust and pollen etc, except that which is caught by
the window screens. I don't know any details about how much the
**Now when I don't run my AC, I leave the windows open 24 hours a day,
with screens, so I get the humidity, but I think I get less dirt,
because the natural breeze is light and I'm not trying to replace all
the air in the house with outside air, every day.
I keep a fan just above my bed, one above my desk chair, and one on
the tv's in the living room and the kitchen. When I'm in a room, I
run that room's fan at a speed where I can't hear it, or can barely
hear it. The fan on the window sill above my bed has a thermostat I
got from an old 21" square fan, that I spliced into the wire, so that
it turns off it if it gets too cold during the night. (Rember that
there are heater thermostats and fan thermostats, and they work
opposite from each other.)
A ridge vent will lower the attic temps better than the powered roof fan
and at no operating cost. I don't currently have a ridge vent here in NY
just because I am too lazy to climb on the roof and put one in. I do
have a ridge vent on our 12' x 16' cathedral ceiling pool house and I
insulated between the 2" x 6" rafters with insulation made for 2" x 4"
walls, allowing 2" of airway from the soffit to the ridge vent. Even
though I have black shingles on the roof, it is always cooler inside
than outside. In my house, I do have continuous soffit vents and a
thermostatically powered gable fan, a whole house fan and Central AC.
I prefer the whole house fan for a number of reasons.
Used sparingly, it can replace all the air in a house, whether it is hot
air, smoky air (burned food), bad smells (spilled chemicals, dog came in
with skunk smell, etc.) and, if I have to go into the attic in the
summer, it will blow all the hot air from the attic, so I can work in
reasonable comfort. They are noisy though, especially when located near
bedrooms when you are trying to sleep.
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