Whole house fan - possible to add variable speed?

[Lee B]

Current house came with a whole house fan (not an attic fan, but the kind in a hallway ceiling that sucks air into the attic). I was happy to see that because I really liked the one in my old house. However the one in the old house had a variable speed dial on it, and the new house's fan has just one speed - high and loud with a simple off/on switch.

Is the variable speed a function of the fan itself or can that be added at the switch? I'd definitely be having an electrician do it, but I'm just trying to figure out if it's even doable, or if I'd end up needing an entire new fan. And if so, would replacing an existing fan and switch be difficult (ie cost me an arm and a leg)?

[DA]

It sucks conditioned air from inside the house into the attic? Is it a finished attic? Otherwise I can't see any logic in using this fan. Sounds like the only speed setting you'd want on it is OFF.

But as far as speed control, it would depend on the type of the motor. It is very likely a single phase AC, and so this controller Grainger sells might work:

(it's only 2.5A but cheap, and they have beefier models, too)

I guess, you'd need to get up there and see the motor first. Getting a wrong speed controller will most likely kill either the motor or the controller.

Good luck!

------------------------------------- /\_/\ ((@v@)) NIGHT ():::() OWL VV-VV

[Ed Pawlowski]

You need a switch that will handle the motor size in question. I cannot imagine running it on high all the time. I ru n mine ab out half speed after the first two minutes or so.

[Ed Pawlowski]

"DA" wrote

Whole house fans suck fresh air from outside through the open windows and door and push it out the attic. On cool nights, it is a very efficient way of cooling down the house. It does not replace AC on hot and humid days.

[JimT]

Only makes since in certain climates. Hawaii would be one. Areas near the coast etc. They work basically the same as a evaporative cooler but without the cooling pads. I've suggested it for people that have a very limited budget and a place to draw cool air in. Better than nothing.

[Oren]

Some homes in SW Georgia (in the late 80's) had just a fan like the OP mentions. It had just a light switch in the hall.

If you had very large shade trees and the Sun was right you opened a window on the cool side of the house. Create a draft. In the kitchen, close all windows and open the back door while cooking. It drafted the heat into the hall fan and out the attic.

At night only open a BR window.

[willshak]

DA wrote the following:

It also sucks non-conditioned air from the house and causes cooling breezes, which is its main function. You'd have to own one to know the benefits. Before AC, fans were the only choice for comfortable air. They still perform the same function. It may be comfortable in the house without AC, but the sun has been beating down on your roof all day, but if you have to go into the unfinished attic to look for something stored away, the fan can replace the hot attic air with outside air from open windows below the fan. Burn something on the stove? The fan can remove the smoky air in the house within a few minutes. You don't have to call the FD to aerate the house. Still smell last night's fish dinner? Suck the smell out of the house. Jasmine came in with the remnants of a meeting with a skunk? OK, you'll have to run the fan a whole lot longer. (N.B.) Jasmine was my Golden Retriever, and yes she did. I have a WH fan and central AC and I use either of them at various times of the year.

[Jon Danniken]

It is a function of the motor, which will be a split-phase induction motor. You either have a motor designed with multiple windings for multiple speeds, or you don't. If you don't, the only practical way would be to replace the motor with one designed with multiple windings, or get a new unit.

If you do have a motor designed with that feature, it will be a simple manner of wiring up an appropriate switch to select between the speeds available.

Jon

[Ed Pawlowski]

"Jon Danniken" wrote

Not quite true. Mine works with a simple dimmer switch of proper capacity. Multiple windings not needed.

[Lee B]

Thanks. Is that something an electrician could tell by looking at the unit? (No point in telling me what to look for, I'm not built for climbing a ladder up into that little trap door to the attic... or worse trying to climb back down!). I got the old fan at Sears and also got the variable speed dial there. I can't remember what I paid for that fan 20+ yr ago, but I know it wasn't a top of the line or anything special. I sort of assumed they all worked the same and was surprised when I encountered this one.

I can't use the fan too often, living in the mid-Atlantic where it's often too humid to suck that wet air in. But we've had a few really pleasant evenings where the humidity was low, and it would be nice to turn off the A/C and feel like I'm saving $.

[Jon Danniken]

Yes, an electrician will know in short order what type of motor is in your unit.

Jon

[LSMFT]

Yes, it's doable. There are variable AC motor controllers. They are not cheap. Might be cheaper to replace the motor with a 3 speed wound rotor motor or a DC motor with speed controller. Electrician can give you an estimate.

[RickH]

Whole house fans are great. Yes you can put on a variable speed controol, but I suggest you over-rate the control amperage you buy by double. For example if the fan draws 5 amps then get a 10 amp control. Also when turning it on make sure the control passes through the higher speed, then you lower it. This is so the motor gets enough starting current. I replaced the Off/High/Low switch on mine with a variable speed. You only use the High speed motor input wire, just cap the low speed wire.

[Nonny]

While a full variable speed controller would be nice, I wonder if it really adds that much to the benefit of the fan. For instance, the louvers of the fans require a minimum amount of pressure differential for the air to open them, eliminating the lowest speeds you could get with the controller. The one I installed in our first house had a 2-speed switch for High/Low operation and we seldom used it in any position other than High. Our second house had two of the fans and again, both were left on High.

If the OP investigates and finds that his fan is a 2-speed one, my suggestion would be to invest first in a DP switch and use the high/low speeds to see if it's worth the added cost of buying a full controller for anything intermediate or lower.

Nonny

[RickH]

I needed a speed adjustor because sometimes you choose to not open enough widows to keep up with the fan draw, so a nice slow fan is nice if you just want one bedroom window open at night. Even on low, may fan was overdrawing most of the time, its a 30 inch belt drive.

Also depending on how much output venting the user has in their roof and eves, a variable speed lets you not overload the amount of air your attic is capable of evacuating. Its cheaper than installing more vents. Also the variable speed saves kilowatts. The louver spring can be easily adjusted to require only a very light amount of air to open them, mine pops open very easily.

[keith]

That depends on the motor. If it's a universal motor it'll probably work fine. If it's an induction motor, probably not. Induction motors tend to be "constant RPM" or with a given load, "constant power" devices. As the voltage is reduced they'll want to maintain RPM, which requires the same power, thus current increases.

If the fan is belt driven it's probably an induction motor.

[Ed Pawlowski]

"Nonny" wrote

I always start my fan on high for a couple of minutes to get the air flowing. Then I can turn it to the lowest setting and it works just fine. I like the variable speed and set it according to the needs at the moment.

[Tony]

If you use an AC motor speed controller it will work fine. It does not control speed with changes in voltage, it changes speed with changes in the frequency. This type of speed control also lets the fan run at lower speeds without stalling. The days of the old rheostats are long gone.

[Tony Hwang]

Hi, Anything is possible. Like infinite speed control tied to the ambient temp. Wonders of electronic engineering....

[krw]

They're a tad expensive for a fan. Have you ever seen one on a whole house fan?