What size fan (30", 24") are you looking for? The desired fan is one that installs horizontally in a ceiling, right? With shutters?

Yes, horizontal in attic, with shutters in the ceiling below. It's not a lot of house so either 30" or 24" could work; a bigger fan running slower would probably be better/quieter anyway (a good reason for the variable speed switch).

Can cut the joists, or not, no concern there. Need shutters but don't mind buying them separately. Also don't mind buying the motor separately if need be.

I am not an electric motor expert, but your question sparked my interest for a solution. The speed of an AC motor is a multiple of the 60 Hz line frequency. The frequency has to be changed in order to change the speed. The speed control you found uses a triac device to change the shape of the sine wave. It will probably work with the motor found on a $350 belt driven whole house fan you can buy at Home Depot or Lowes. However it could cause the motor to overheat. You could buy the fan and before installing it connect it to the variable speed switch as a test. This will allow you to see how much is the speed variation, if the motor gets too hot, and if motor emits a humming sound.

Another way to do this would be to replace the AC motor with a DC motor. DC motors are much more expensive and then you would need to find a compatible speed controller. The high expense is probably the reason you can't find a whole house attic fan with a variable speed DC motor.

@mike_home Thank you.

While they didn't explain why, I suspect this is why the manufacturers where saying a variable switch would burn up their motors. I called a few before making this post, specifically including to the ones making the brands sold in the big box stores, IIRC. I can't see buying and burning up those particular fan motors on a gamble when they said it wouldn't work.

I'll take a stab at finding the right DC motor, but am not very confident in this area where I'd be likely make a purchase, plus then I'd have to do some sort of conversion from AC power, not sure what's involved with that, only ever did the other direction from car batteries to power some small things like lights/hand-tools. I know the variable switch emits some heat, but they have heat syncs for that reason, not as scared by that so long as I can match the rated amperage.

Whole house fans used to be common in the market with variable speed switches, can't figure out why they're so hard to find now...

Re “why they’re (sic) so hard to find” is because of: noise and fire codes.

Those fans were 80’s technology.

@mike_home

Grainger has a motor-buying tool to narrow down to an application; this DC motor is a budget buster as you said to expect, but fits the description you gave, I think:

https://www.grainger.com/product/DAYTON-DC-Permanent-Magnet-Motor-2M509

Is this what you had in mind?

That motor is 1/3 HP at 1800 RPM and would seem a good fit for an attic whole house fan. There is a second one listed for $399 which is a good candidate. Grainger also has 90V variable speed controls.

You would think someone would have a better solution on the market.

mike, if you were licensed......and insured, you would know why.

there is a reason why those whole house fans are not available. Something about house fires.

@User not sure what info you're contributing, but let's not take down those trying to help. I think it is just that the solid state switches can eventually fail, especially if they don't have a high enough amperage rating compared to the motor.

Jim,

Whole house fans are readily available. I would not recommend them for any house that has central air where the windows are kept closed in the summer. I agree turning on the fan with the windows closed would be dangerous if you have any gas appliances. My comment about a better solution was for a variable speed electric motor. Tesla won the current wars over Edison and now we are stuck with all these AC motors.

Doug,

I know you said you are not interested in a 2-speed fan. Would 3 or 4 speeds be of interest at a reasonable cost? You could find a 1/3 HP blower motor with multiple speeds for less than $100. You could then wire it to a rotary switch to select one of the speeds. That the ideal solution be may be a good compromise at a reasonable price.

Whatever you do please use caution.

Doug, those fans do not meet fire codes.

I have had two whole house fans in California. First one was in the early 80’s. It was replaced in 2010 because it did not meet fire code. The 80’s fan was a ceiling mounted “air plane “ fan with the lead fire safety thing. When I had A/C installed in 2010, my fan did not meet code. The whole house fan was replaced with a local fire code compliant fan. Same “hole/whole” just a different fan.

Does your fan meet local fire code?

@mike_home I suppose at a point, having many speeds to choose from gets close enough for me if true variable speed becomes impractical. The 2 speed motors hardly seemed to have much CFM difference between the high and low, probably because they're trying to stay above what is needed to keep the louvers open. I get it that a minimum draw is needed to keep the louvers open if relying on gravity, so that'll be my problem to resolve if the lowest speed is under that. I suppose if the 'low' setting isn't low enough I can look at reduction ratios on the belts.

I may have just found an old fan & motor. Seems a little silly to go that route but could get it done.

@User I don't want to burn my house down for sure and am not going to rush into anything since this isn't an area of expertise. That said, there needs to be some evaluation of risk versus benefit where I can acknowledge and accept risk (am the homeowner), which I suppose would need the 'why' behind whatever the code states. Rather than get into all that though, is there a way you'd be comfortable with that provides more control over fan speed even if it isn't exactly like we had in the good old days?

IF, a fire started inside your home, AND the whole fan was running.......

My old “air plane” fan had a lead (metal) link in case of fire.

Doug, there is a reason why those fans are not available for home use....noise, fire codes.

Those fans were loud.

Why the desire to use 80’s technology? Is this a budget issue?

I'm not doubting they can be loud in the general case, but the one I had was quiet, especially on a slower speed, and was great to run low all night. If you really cranked it then it got loud, but you'd be enduring hurricane force winds throughout the house. The solid state switch was barely warm, didn't seem too concerning. If I had some 1989ish fan like that I'd just keep it running and change belts or whatever, but this is a new remodel situation and we can do whatever. Prefer fresh air over AC and often would just open the windows and run the fan at night, close the blinds during the day and that's it for cooling most of the year.

Budget is of concern to be sure, but I am especially trying to be able to run slow, partly because the attic space is small, possibly too small for higher speeds. This is also to keep noise down since it is close to sleeping areas. It's a finished attic, so the actual 'attic' that remains outside the conditioned air space is fairly tight; I'll be able to ensure I have a lot of net free venting and just enough clearance, but it certainly won't be roomy and might overwhelm the cavity at higher speeds leading to noise/cavitation. If I buy a 2-speed fan and the low setting is too loud or has too much CFM, then there won't be much I can do at that point.

Re attic space, there are tables.

Good luck with installing DIY whole house fan.

@kevin9408 Thanks, that's good stuff. I'm going to have to look some of these things up, I'm not at that level, but the exercise of doing it comes with the benefit of learning. I do get Mike's point about running a draft through a house that has a fire in it since you'd be adding oxygen to a fire, but it's just a risk I'm ok with. Have a wood stove for heat and buck up my own trees with a chain saw, should paint the risk tolerance picture ...

Hi Doug,

What you want is not available in California as a commercial product.

The Whole House Fan works well in some areas. I live in California, where it can get warm during the day, can be cool at night. I depended on the fan until ~2010. I had A/C installed, the City inspector did not like my Smoke Detectors, nor Carbon Monoxide Detector, nor my attic fan.

I had a code compliant fan installed.

Some code things are “grandfathered”, some are not.

@User I did some time in Cali near Sac, so I can relate to the regs & weather somewhat, could get hot during the day but cooled off nicely at night and was rarely humid. I did peruse Title 24 but am still not quite sure what makes for a code-compliant fan. It's moot in any case, I now live in a rural area in another state where we have virtually zero permitting or zoning or any of that; there will never be a time someone is in my house to inspect anything, at least until I sell where they can inspect/appraise/offer as they wish.

For the fan here and now, I'd like it to be relatively effective and safe; I'm ok with a fan that might get you hurt if you're stupid (overloading a solid state switch, not opening windows and sucking in soot or carbon monoxide, etc.), but I *do* want to avoid causing a fire in the attic just by turning the thing on one evening, sort of why I'm doing this whole exercise to begin with.

I did look for tables on the attic sq ft requirements as you suggested but I don't think it'll end up mattering as much as the intake/exhaust venting throughput do by what I've read. I'm thinking I'll buy a belt-driven fan, see how that suits while I work on eventually putting together and mounting variable speed components like Kevin described (which would take more time, if not money); I'd need the fan blades and assembly from that anyhow.

Maybe I will see you on cable TV sometime, one of the DIY/Wilderness Shows.

Didn't know anyone still watched cable. It definitely wouldn't be Reality TV if I'm on it providing DIY or lifestyle tips...

Doug if you used a PID controller set to auto tune your system could be 100% automatic. The PID, once set with your parameters will learn and can adjust and vary the fan speed depending on temperatures you input. Great project, and a great application for a PID. This isn't an insult but if you google "PID for dummies" you can study up to see if it's something you may like to work on.

@kevin9408 That'd could be really cool, especially without needing to go the whole internet-connected smart-house route to do it, I'll definitely check into that too. It's a gutted house with no electric at the moment, I'm going to put a OTS fan in and do all the framing, insulation and whatnot so I can get to moved-in, then circle back to the fan. I'll put in a word with an HVAC contractor to watch for the parts in the interim. It'll be a few/several months to get this but it'll be a fun winter project with the kids. Thanks for replying/putting thought into this.

Have you tried a place that sells and repairs electric motors, the type of place that looks industrial and closes around 4PM? They might even have an off-the-shelf solution for you.

The link is for information purposes only as I don't think you are willing to drive all the way to Montreal, Canada just to get a fan motor.