Air filtration w/ whole house fan

[Jim Brown]

A guy I work with just gave me a never-used whole house fan (24" diameter). I don't need it for its intended use, so I'm thinking about making a downdraft sanding table / air filtration device out of it. I don't know how many CFM this thing will move, but if it's anything like the one we had in our old house, I think it will do the job.

I'm considering a design like this

with a timed switch.

So ... before I embark on this project ... can anybody tell me why this is a bad idea? I'm grateful for any wisdom you can toss my way.

Jim Brown in PA

[Larry Jaques]

The motor most likely isn't rated for hazardous duty like a dust storm, Jim, so it'll likely burn out very early. Hopefully it won't cause a fire while doing so. Use it to ventilate the shop, not the sanding table. Figure 800-1,000 CFM.

I had a 30" 2-speed and adored it in the hot summer months in LoCal. I could come home after work, 90F inside the house, and in 15 minutes, the inside air matched the 75F outside air. It was used as a whole house fan, BTW.

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[J Brown]

Larry Jaques wrote in news: [e-mail]:

Thanks, Larry. Had one in a house we rented in SC, and it was great in the spring and fall ... the louvres were rather noisy but tolerable in short bursts. There was another fan in the other end of the attic to help the hot air on its way out. Here in northeast PA we don't have as much need, and I'd have to get a louvred ceiling kit for it, so it's not worth the trouble to use as a whole house fan.

This basement is a whole 'nother story ... two tiny windows in one end of the place (one leading to the coal bin), no door to the outside, and when we bought the house, no straight shot down the stairs, so forget about even getting a sheet of plywood down there. Electricity? One outlet and four single-bulb lights for more than 2000 square feet. We added a door from the garage to the cellarway, so at least we can get 4x8 sheet goods up and down the stairs now. But there aren't lot of options for ventilation ... hence my interest in pulling some of the dust out of the air. I didn't like working out of my garage, but I miss being able to raise the doors and fire up the leaf blower ...

[RonB]

Not disagreeing outright but don't underrate the environment a whole house fan has to live in (hot, insulation, dusty). This is probably a better application for a squirrel cage blower but I have seen several examples of sanding tables and dust filtration systems made from these fans.

[Robert Bonomi]

The kind of fan you have is designed to move large volumes of air against virtually -zero- resistance. OK for an "air cleaner", not so good for the sanding table. (squirrel-cage blowers -- like the woodcentral pictures show do a _much_ better job of moving air against some resistance.)

It needs 3-4 sq ft of "unrestricted" air intake, and the same for the outflow.

For air filtering: Using 'el cheapo' fiberglass filters, figure minimum 50% more cross-section. Using 'high grade' pleated ones, double the original numbers. at least.

In addition, you need the filters 'far enough' away from the fan itself, that it draws relatively evenly through all the filter surface, *not* just the area directly in front of the blades.

With elcheapo filters, I'd go for something like 4 16"x20" ones, spaced about 3' in front of the fan.

[Larry Jaques]

The evidence makes it clear that you should simply make a proper dungeon out of the basement and build a REAL shop out back.

Heh heh heh. I need to do that again, too. I just clea^H^H^H^Hstraightened up the shop and need to finish blowing out what didn't get sucked up by the DC or swept up. While the floor sweep is a definitely nice addition to the DC, a leaf blower gets into those crevices that the brooms and vacs miss.

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[J Brown]

[e-mail] (Robert Bonomi) wrote in news: [e-mail]:

I think go this route ... make a filtered air cleaner. The sanding table can come later, either with the DC or a squirrel cage. Thanks for the advice. When I get it done, I'll make a report.