Whole house fan -- belt or direct drive?

[Wild Turkey]

LOML wants a whole-house fan for those days when it's very pleasant outside but no wind -- we have quite a few days like that -- or when Fescue cooks something and fills house with smoke or pepper fog


I'm having a hard time choosing between direct and belt drive.  Belt drives will eventually need maintainence but I'm afraid a direct drive will burn out the motor.

Anyone with much experience?

[fixtureman]

I have had my belt drive for over 40 years and it just needed a new belt.

[fredhargis]

When we had one I insisted on belt drive. That worked out very well for the time (8 years) we had it.

[Admiral]

My brother is going on 35 years with his belt drive and hasn't done a thing to it. Not that he would know how to fix anything, I was in the mechanical line when genes were handed out, he was in the personality line, so when something goes kaput in his house I get the call.

[TDKPE]

LOML wants a whole-house fan for those days when it's very pleasant outside but no wind -- we have quite a few days like that -- or when Fescue cooks something and fills house with smoke or pepper fog


I'm having a hard time choosing between direct and belt drive.  Belt drives will eventually need maintainence but I'm afraid a direct drive will burn out the motor.

Anyone with much experience?

I've had a number of whole house fans.  My last house was the best with a 36" Chelsea panel fan, which hung on chains on springs with a cloth plenum to the outside wall.  It had a single-speed motor, but I replaced it with a 3-speed (which is now in my air filter in the basement
).  Normal rated speed was only 400 rpm, so it was very quiet.  The motor I put on was 1800/1200/900 rpm, and at 200 rpm fan speed you couldn't hear it run at all, and it was in the gable end of the house right over my head in the attic and pulled a nice gentle breeze through all the upstairs windows for sleeping.

One big advantage of belt-driven designs is that you can change max speed simply by changing sheaves.  For a fan like that, cheap die-cast sheaves are fine.  If you go that way, get a 2-speed model, as it'll have an 1800/1200 rpm induction motor (super common), and running at 2/3 speed is a lot quieter than at full speed.  But you can always slow it even more with a sheave change.

I'm guessing you're considering putting it into an upstairs hall ceiling.  Mine was in the gable wall, so it had two shutters.  I added a shutter motor to the outside wall shutter, and the ceiling shutter already had one.  If mounting the fan in the ceiling, you probably won't need a shutter motor unless you slow the fan down to where it can't pull it open.

I have pics of the installation somewhere but can't find it right now.  Below is some generic pic of the same unit, and my old house with the shutter visible.

[attachment=27379]

[attachment=27380]

If you do ceiling mount it, the blades will made a good bit of noise simply because they're close to the shutter.  You can quiet it down by either building a chimney to raise it up, or better, a right-angle duct elbow (out of plywood) and mounting it so the shaft is horizontal.  It'll be much farther from the shutter, and you can use some interior duct insulation to dampen some noise.  If you have the room, mounting it another 8 ft away at the end of a big square duct (since it's plywood) would be even better.  And use resilient mounts, as the sound will travel through the structure.

Speaking in general terms, for the same air flow, larger and slower is quieter than smaller and faster.  And by the affinity laws (aka 'fan laws' or 'pump laws'), the air flow varies with the speed, the sound generated varies as the square of the speed, and the power required varies with the cube of the speed.  So if quiet is a primary concern, get a large one and slow it down if it's too loud.

[Cooler]

I have a belt drive whole house attic fan for 22 years.  The beginning of last summer it stopped working so I bought a new one and my handyman was going to install it, but found that a wire had pulled loose.  So now I have a spare fan.

Belt drive fans are quieter than direct but still noisy.

I fantasized building a small shack outside my house and setting the attic fan in the shack and running a duct up to the attic and through the same vent as an attic fan.  That would be quiet, but would look like a mess from outdoors.

Adding a transom to bedroom doors allows you to close the door and still get the effect of ventilation.  You get ventilation and privacy that way.

It brings in dust and pollen.  

I have had two different controllers for my attic fan  at different times.  I used to have a timer.  I set it to go off when I left for work and to cycle back on 30 minutes before I got home.  That worked well enough.

I then switched to a thermostat.  That is much better.  My electrician had a hard time locating one to work for this application.  My only issue is it has an accuracy of ± 4 degrees.

So if I set it on 70 it will go on, but likely will not cycle off until it gets to 66 degrees.  And it won't cycle on until it gets to 74 degrees.  It does not sound bad, but it is enough to make you feel cold at night before it finally cycles off.  Some nights I walk up to the thermostat and tap it and it will cycle off. 

It would be nice to find a thermostat that is more sensitive. 

I do have A.C., but I only use it when the humidity is high and the temperature is well above 80 degrees.  

It does bring in dust and pollen.  And you do need adequate venting for the hot air to exit the attic.  If that is not supplied, then the hot air will exit the soffit vents and can be sucked right back into the house through the nearby windows.

Even if you have air conditioning, running the attic fan will purge the attic of the super-heated air and make the A.C. more efficient.

[TDKPE]

I then switched to a thermostat.  That is much better.  My electrician had a hard time locating one to work for this application.  My only issue is it has an accuracy of ± 4 degrees.

A house I used to rent many moons ago had an attic fan in the hall ceiling (quite noisy), with a thermostat that you had to manually start, but it would shut off automatically.  I've never seen one like that since, and I've looked.  

That style won't allow it to start automatically, especially when you don't want it to start, but for night cooling, it shuts the fan off once the interior temperature goes below the set point.  Saves you from having to get up in the middle of the night to shut it off.

Oh, and those Chelsea fans came with a fire switch, which was basically just a normally open toggle switch that was held closed by a soft link that would let go in a fire, shutting the fan off if it was running.

[Cooler]

A house I used to rent many moons ago had an attic fan in the hall ceiling (quite noisy), with a thermostat that you had to manually start, but it would shut off automatically.  I've never seen one like that since, and I've looked.  

That style won't allow it to start automatically, especially when you don't want it to start, but for night cooling, it shuts the fan off once the interior temperature goes below the set point.  Saves you from having to get up in the middle of the night to shut it off.

Oh, and those Chelsea fans came with a fire switch, which was basically just a normally open toggle switch that was held closed by a soft link that would let go in a fire, shutting the fan off if it was running.

When I didn't have a dog or cat, the timer was very good. It only went on a half hour before I came home, at which time I either left it as is, or switched to the A.C. 

With the pets in the house I wanted the fan to come on.  And if it promised to be over 90 that day I left the AC on for them (and for me, but don't tell anyone).

[Stwood_]

Belt drive fan here.

[Wild Turkey]

Picked up a belt drive this morning. I will discuss the installation with the contractor tomorrow.

Thanks for the advice!