(Lacustral) writes:

I'd like to use an exhaust fan (fan from a ceiling grille to outside) to
run overnight in the summer, with the windows open, so that my house is cool
in the morning. I'm not sure how much CFM is needed. I don't want a big
powerful whole house fan because I'd like it to be quiet. Just a small
fan that keeps running overnight.

I had a wholehousefan growing up. It was large, but it wasn't that
loud.

The thing to know about fans is that you can have a large one with a
relatively low rpm, with a solid well constructed motor that moves the
same volume of air as a smaller one wizzing at deafing volume and rpm
with a cheaper motor.

My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.

Best Regards,
--
Todd H.
http://www.toddh.net/

Todd H. ) wrote:
My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.

I don't need a 1000 CFM whole-house fan - I don't need something to clear
out the house air in a few minutes. It would require larger ducts and be
more of a hassle to install.

Laura

Lacustral wrote:

Todd H. ) wrote:

My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.


I don't need a 1000 CFM whole-house fan - I don't need something to clear
out the house air in a few minutes. It would require larger ducts and be
more of a hassle to install.

Laura

Most whole house fans dont use ducts. They simply vent air from the
living space to the attic where it is forced out through gable, ridge,
soffit, roof, vents.

Your question can simply be answered by how quickly you want to change
the air in your home. If you want to cool your home in 1 hour then a fan
that exchanges your homes volume 2-3 times an hour would likely be
adequate. If you are going to leave the fan running longer and cool the
home slower/continuously exchanging the homes volume once every 2-3
hours would be fine.

It will really depend on how you intend to run the fan and how quickly
you will want to cool the home. I agree with Todd that a variable speed
fan will likely be best for any application as it will allow you to run
it for long periods on low to maintain airflow but also allow you to
kick it up to high for a quick purge/cooldown should you need it. Of
course controlling it thermostatically would be the best.

Mark

"M&S" wrote in message
nk.net...
Lacustral wrote:

Todd H. ) wrote:

My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.


I don't need a 1000 CFM whole-house fan - I don't need something to
clear
out the house air in a few minutes. It would require larger ducts and
be
more of a hassle to install.

Laura

Most whole house fans dont use ducts. They simply vent air from the
living space to the attic where it is forced out through gable, ridge,
soffit, roof, vents.

Your question can simply be answered by how quickly you want to change
the air in your home. If you want to cool your home in 1 hour then a fan
that exchanges your homes volume 2-3 times an hour would likely be
adequate. If you are going to leave the fan running longer and cool the
home slower/continuously exchanging the homes volume once every 2-3
hours would be fine.

I have used "attic fans" with limited results for years.

The temp difference, size and materials of the space are what is important.
In my humble attempts if there is less than 10 degrees difference the fan
does squat to very little difference. My home is masonry and has R-40+ in
the attic.

The fan I use is 6000 cfm. Roars like a banshee. I pull the air from one end
of the house to the other. It takes at least 3 hours of 10 degrees
differential to lower my home 1 degree F. Running all night sometimes I can
achieve a 10-15 degree drop. If the differential is greater than 10F then
the results are better. Still takes over night with the banshee running. My
home is ~1100 sqft with 8.5' ceilings.

Your probably wondering if I have tried a smaller fan, yup done that and
bought the T shirt. The banshee works.

Your results will vary

On 05 Jun 2006 17:08:16 -0500, (Todd H.) wrote:

(Lacustral) writes:

I'd like to use an exhaust fan (fan from a ceiling grille to outside) to
run overnight in the summer, with the windows open, so that my house is cool
in the morning. I'm not sure how much CFM is needed. I don't want a big
powerful whole house fan because I'd like it to be quiet. Just a small
fan that keeps running overnight.

I had a wholehousefan growing up. It was large, but it wasn't that
loud.

We had one too, but it was before they invented speed controls. And
it was only 4 feet from my head (and then go up to the ceiling). So I
hated the noise.

My mother had also given me an alarm clock that ticked. Life was
hell.

But I revolted and demanded an electric alarm clock, so she got one
out of the closet, and we actually turned off the fan before bedtime.
Life was pretty good, come to think of it.

But now they have speed controls which makes all the difference.

The thing to know about fans is that you can have a large one with a
relatively low rpm, with a solid well constructed motor that moves the
same volume of air as a smaller one wizzing at deafing volume and rpm
with a cheaper motor.

My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.

I must say that the whole house fan must have moved 100 times as much
air as my little bathroom fan. Maybe 500 times, although Im just
guessing.

Since I'm here, I'll express my preference for roof fans.

Best Regards,

"Lacustral" wrote in message
...
Todd H. ) wrote:
My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.

I don't need a 1000 CFM whole-house fan - I don't need something to clear
out the house air in a few minutes. It would require larger ducts and be
more of a hassle to install.

Laura

Don't forget that the walls and floor are warm not just the air. In other
words if you just change the air once and then stop the walls will warm the
air up again. You may need to change the air numerous times before the
temperature of the whole structure comes down.

SQLit wrote:
"M&S" wrote in message
nk.net...
Lacustral wrote:

Todd H. ) wrote:

My gut--without researching anything for you--is that a variable speed
whole house fan is probably what you actually want.


I don't need a 1000 CFM whole-house fan - I don't need something to
clear
out the house air in a few minutes. It would require larger ducts and
be
more of a hassle to install.

Laura

Most whole house fans dont use ducts. They simply vent air from the
living space to the attic where it is forced out through gable, ridge,
soffit, roof, vents.

Your question can simply be answered by how quickly you want to change
the air in your home. If you want to cool your home in 1 hour then a fan
that exchanges your homes volume 2-3 times an hour would likely be
adequate. If you are going to leave the fan running longer and cool the
home slower/continuously exchanging the homes volume once every 2-3
hours would be fine.

I have used "attic fans" with limited results for years.

The temp difference, size and materials of the space are what is important.
In my humble attempts if there is less than 10 degrees difference the fan
does squat to very little difference. My home is masonry and has R-40+ in
the attic.

The fan I use is 6000 cfm. Roars like a banshee. I pull the air from one end
of the house to the other. It takes at least 3 hours of 10 degrees
differential to lower my home 1 degree F. Running all night sometimes I can
achieve a 10-15 degree drop. If the differential is greater than 10F then
the results are better. Still takes over night with the banshee running. My
home is ~1100 sqft with 8.5' ceilings.

Sounds pretty much like my experience. I'd been idly wondering if
having the fan mounted in the attic in front of a vent or something
instead of in the ceiling would be quieter, but now I have AC. Oh joy.

In article ,
says...

Is that other people's experience? That taking cubic feet of airspace to
been cooled, multiplying by the fan's CFM, times a fudge factor of 2-3,
would give you about how long it takes to exchange out the air in the
airspace?

I just need to exchange the air on about 4800 cubic feet. Not
to have the fan strong enough to set up a breeze you can feel.

If I were exchanging the air 2-3 times/hour as you suggest, that would
be a 240 CFM fan. If I were only exchanging air every 2-3 hours that
would be a 40 CFM fan.

Just double-checking, do you have a very small home? 4800 cubic feet
would be a 600 square foot house with 8-foot ceilings. A 240 cfm fan
*would* be enough to create a breeze you could feel in that small a
space.


--
is Joshua Putnam
http://www.phred.org/~josh/
Updated Bicycle Touring Books List:
http://www.phred.org/~josh/bike/tourbooks.html

I don't know how many cubic feet I have, but my house is about 1600 sq.
ft. and I have 10-foot ceilings downstairs, 8 feet upstairs. When I
put my box fan in an upstairs window and open windows downstairs, I can
literally feel the breeze coming up the stairs. The method that works
best for me is to open windows at night and put the box fan in the
window blowing out, which exhausts the hot, stale air in the house and
brings in the cool night air. During the day, I keep the windows
closed and curtains pulled where the sun is coming in. I don't open up
again until it cools off in the evening. My house is well insulated
and has good windows but, at 100+ years old, is far from airtight.
This method works really well except during periods of hot, humid
weather when it stays hot at night. At that point I resort to a couple
small (5K) air conditioners and put my box fan on the floor to
circulate air. It's not high tech, but it works great.

Jo Ann

Joshua Putnam wrote:
In article ,
says...

Is that other people's experience? That taking cubic feet of airspace to
been cooled, multiplying by the fan's CFM, times a fudge factor of 2-3,
would give you about how long it takes to exchange out the air in the
airspace?

I just need to exchange the air on about 4800 cubic feet. Not
to have the fan strong enough to set up a breeze you can feel.

If I were exchanging the air 2-3 times/hour as you suggest, that would
be a 240 CFM fan. If I were only exchanging air every 2-3 hours that
would be a 40 CFM fan.

Just double-checking, do you have a very small home? 4800 cubic feet
would be a 600 square foot house with 8-foot ceilings. A 240 cfm fan
*would* be enough to create a breeze you could feel in that small a
space.


--
is Joshua Putnam
http://www.phred.org/~josh/
Updated Bicycle Touring Books List:
http://www.phred.org/~josh/bike/tourbooks.html

Lacustral wrote:
Joshua Putnam ) wrote:

Just double-checking, do you have a very small home? 4800 cubic feet
would be a 600 square foot house with 8-foot ceilings. A 240 cfm fan
*would* be enough to create a breeze you could feel in that small a
space.

Actually it's 640 sq feet (just measured it). x 8 feet high, = 5120 cubic
feet.

Laura


Stick a 3 speed 20" box fan in one of the upper room
windows.......blowing outward. Place a carboard shield on the sides as
needed to create a reasonable seal.

Open windows in the rooms you want to cool (open more windowns or open
them further in the "most impotant" rooms to cool)

The rooms with the open windows will cool FIRST & the room with the
fan will cool LAST.

Experiment with fan speed & window opening, adjust window openings &
fan placement to get the desired result.


fwiw I have a 2300 sq ft home in OC SoCal. It's a 1.5 story design
built in 1930 We typically get good nightime cooling (into the low
70's or less with low humidity) we can get temps in the mid / high 90's
& even low 100's.

I used to have a Nat Gas AC unit but it bit the dust & I haven't
replaced it.

A single 20" box fan funning on high speed will cool the house to
outside temp by morning & will provide a comfortable (& adjustable)
breeze in the bedrooms.

cheers
Bob