I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

On Mon, 07 Feb 2005 22:02:05 GMT, habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan.

If you've got decent wind, windows and draft can do a very good job
without power.


I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

Look at options for heat exchangers, and see what gets you the right
number of changes of air per unit of time. I forget how many changes
of air you're supposed to have per day to have good ventilation, but it's
a surprisingly high number.

It also might help if you say what climate you live in.

"habbi" wrote: (clip) Can any motor be slowed with a speed control (clip)
^^^^^^^^^^^^^^^^
No. Undoubtedly, your fan will be driven by an induction motor. They do
not respond to the usual speed control methods. The easiest way to reduce
the volume of air would be to partially close the open windows. Think of
the windows as valves.

6 changes per hour is considered about right.
Don't bother fitting a sped controller. Just put a damper in the exhaust
from the fan and adjust it to what you want.


"Dave Hinz" wrote in message
...
On Mon, 07 Feb 2005 22:02:05 GMT, habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My
idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I
want
it for cooling the house in the summer. Open the a window at opposite
end of
house, open window in the door between garage and turn on fan.

If you've got decent wind, windows and draft can do a very good job
without power.


I have no
idea what CFM to get but was thinking about an 18" model rated at 3200
cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is
moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

Look at options for heat exchangers, and see what gets you the right
number of changes of air per unit of time. I forget how many changes
of air you're supposed to have per day to have good ventilation, but it's
a surprisingly high number.

It also might help if you say what climate you live in.

I thought about that but the velocity of the air would increase creating
more noise. the other option would be to bend the fan blades to reduce the
pitch.


"Leo Lichtman" wrote in message
...

"habbi" wrote: (clip) Can any motor be slowed with a speed control
(clip)
^^^^^^^^^^^^^^^^
No. Undoubtedly, your fan will be driven by an induction motor. They do
not respond to the usual speed control methods. The easiest way to reduce
the volume of air would be to partially close the open windows. Think of
the windows as valves.

habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

Better check the building code carefully before
you put much money into this scheme. Most places
want a fire-rated wall and door between the garage
and living-space. They might not allow the window
in the door.

I thought about that but the velocity of the air would increase creating
more noise. the other option would be to bend the fan blades to reduce the
pitch.


I think a variable speed fan motor would be way handy. If you shop used
(ebay) a three phase motor and VFD control would be one way to go.

Another route would be a DC motor and speed control. A place called surplus
center has them both.

Karl

habbi wrote:

I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage.

Can these be slowed down if to much air is moving.


The attic exhaust fan I bought at HD came with a speed control.

Kevin Gallimore

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If you can figure out how to pull the air from close to the top of the
vaulted ceiling. The air there will be warmer. It would be really
nice if you could design it so the fan will pull the air from the top
of the valted ceiling and either direct it into the garage or back into
the house. Then you could use it in the winter to prevent the air from
stratifying and to cool the house in the summer. Blowing air into the
garage will get rid of welding smoke. Probably not sawdust.


Dan

That fan is more likely to be too small than too large. Look at
Grainger for recommendations on attic fans.

Dan

We do this at our 1300 sq ft. house, we have a 24 inch fan with two
speeds, and basically use the slow speed all the time. Our fan moves
air from the garage to the attic.

During the day, we open the big garage door an inch, and turn on the
fan. This keeps the attic and garage cooler. The windows in the house
are kept closed. When the sun goes down, we close the garage door and
open the door between the garage and the house. We then open some
windows in other parts of the house to cool down the house. (We live in
a dry climate with typically 30 degree day-night temperature swings).
In HVAC terminology, this is a night cooling system. My spouse does not
really understand how to use the system to best advantage. For example,
if you want to cool the bedroom, you open the bedroom windows and close
all the other windows in the house. She just doesn't grasp that closing
windows in one room cools another room more quickly. The airflow in the
one bedroom can be pretty substantial if all the other windows are
closed. I doubt if you will need to or want to slow the fan down.

The system works well for us, except on the hottest days.

As someone else said, this is almost certainly a code violation, due to
the requirement of a 45 minute firewall between the attached garage and
the house. As soon as you prop the door open between the garage and
house you are in violation.

If you are designing a new house, build in an exhaust fan for the attic
that comes on automatically whenever the attic gets hot. You can build
in a separate fan between the house and the attic or the house and the
outside for night cooling. If you want to automate it you will need
something called a differential thermostat that compares inside and
outside temperatures. (We have an inside-outside thermometer which lets
us determine when to start night cooling). Then you would have a
separate exhaust fan for the garage. Note that window fans will also
work for night cooling of the house, but you might need more than one
fan. That is the code way, and the best way to do it.

My two cents, or maybe a dime since I actually do what you say you want
to do, practice being worth more than theory.

Richard


habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

Almost forgot. We quieted the fan considerably by mounting it on foam
rubber, prevented the fan vibration from transmitting noise to the
rafters. Well worth the trouble.

Richard


habbi wrote:

I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

Richard,

Be careful...a fire in the garage would take your house down faster
than you could believe it could.

A neighbor of mine years ago had a similar setup.

The wife had just gotten home and had driven the car into the garage.
She then proceeded to go next door for a FEW MINUTES (less than five
minutes). When she came back, the house was engulfed in flames. The
house was a total loss along with their pets.

It would seem that the car had an engine fire and the air movement
through the house had spread the flames and had fanned the fire.

They were very lucky not one died in the fire.

While the reasons for code requirements may not be readily apparent,
they often are created after someone's death points out a design
oversight.

TMT

On Mon, 07 Feb 2005 23:03:39 GMT, "habbi"
wrote:

I thought about that but the velocity of the air would increase creating
more noise. the other option would be to bend the fan blades to reduce the
pitch.


"Leo Lichtman" wrote in message
...

"habbi" wrote: (clip) Can any motor be slowed with a speed control
(clip)
^^^^^^^^^^^^^^^^
No. Undoubtedly, your fan will be driven by an induction motor. They do
not respond to the usual speed control methods. The easiest way to reduce
the volume of air would be to partially close the open windows. Think of
the windows as valves.



It depends on how the motor syarts but some fan motors are speed
variable by voltage reduction. If the motor has a centrifigul starting
switch then you cannot lower the speed. If however, it does not then
you can try supplying lower voltaand see what happens. The motor may
heat up too much. But you can feel the motor and tell way before any
damage can occur.
ERS

habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

As others have said, this can be a bad idea for fire reasons.

If I was doing it, I'd want to make the inlet from the house through a
couple of meter conduit, with a couple of doors set to fall on 45 degree
closures, at the failure of a fusible link (both doors at once) at 50C or so.

I would be more tempted to seperate out the two fans.

I ordered the 24" model which is rated at 4200cfm. Do you know what yours is
rated at? My climate is eastern canada
0-85 F. What type of rubber foam exactly did you use for mounting.

wrote in message
...
We do this at our 1300 sq ft. house, we have a 24 inch fan with two
speeds, and basically use the slow speed all the time. Our fan moves
air from the garage to the attic.

During the day, we open the big garage door an inch, and turn on the
fan. This keeps the attic and garage cooler. The windows in the house
are kept closed. When the sun goes down, we close the garage door and
open the door between the garage and the house. We then open some
windows in other parts of the house to cool down the house. (We live in
a dry climate with typically 30 degree day-night temperature swings).
In HVAC terminology, this is a night cooling system. My spouse does not
really understand how to use the system to best advantage. For example,
if you want to cool the bedroom, you open the bedroom windows and close
all the other windows in the house. She just doesn't grasp that closing
windows in one room cools another room more quickly. The airflow in the
one bedroom can be pretty substantial if all the other windows are
closed. I doubt if you will need to or want to slow the fan down.

The system works well for us, except on the hottest days.

As someone else said, this is almost certainly a code violation, due to
the requirement of a 45 minute firewall between the attached garage and
the house. As soon as you prop the door open between the garage and
house you are in violation.

If you are designing a new house, build in an exhaust fan for the attic
that comes on automatically whenever the attic gets hot. You can build
in a separate fan between the house and the attic or the house and the
outside for night cooling. If you want to automate it you will need
something called a differential thermostat that compares inside and
outside temperatures. (We have an inside-outside thermometer which lets
us determine when to start night cooling). Then you would have a
separate exhaust fan for the garage. Note that window fans will also
work for night cooling of the house, but you might need more than one
fan. That is the code way, and the best way to do it.

My two cents, or maybe a dime since I actually do what you say you want
to do, practice being worth more than theory.

Richard


habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My
idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I
want
it for cooling the house in the summer. Open the a window at opposite
end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200
cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is
moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

On Tue, 08 Feb 2005 04:16:57 GMT, Richard Ferguson
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email
My spouse does not
really understand how to use the system to best advantage. For example,
if you want to cool the bedroom, you open the bedroom windows and close
all the other windows in the house. She just doesn't grasp that closing
windows in one room cools another room more quickly.

Hehe! I would advise "Buy and airconditioner, then!" but my SWMBO
cannot even handle that. There are all these complex bits, like
louvres that actually make the air cooler near you, and controls for
temperature. I just go by these days and fix it after she has turned
it on. I used to tell her, and we would argue, then I would correct
it, and we would argue. Now I just check it. After 5 years it's right
_most_ of the time.

She is not dumb by any means. She is an uppermiddle level exective.
She has degrees and left high school with good marks. But things are
supposed to be there to _work_, just as they are.

I fly trick kiste ( that typo s why I don't call them stunt kites
G)just to relax from time to time. One time I let my mother have a
go. She managed to stop pounding it into the ground, but then it got
to the top of its flight and she said "What does it do now?".
"Whatever you want. Pull a string gently, and it will go that way" sez
I. "But what does it _do_?". The tone was one of almost panic. IT was
supposed to _do_ something.

She _asked_ to use it after she had seen what it did.....

Real non-PC comment. I reckon the glass ceiling cuts both ways.

I have no doubt that my balls will not end up in my court after this!