DIY Shop air cleaner?

[James Williams 007]

I've assembled the parts to make a good quality air cleaner for my small shop.

- Furnace or squirrel cage fan
- variable speed switch
- timer
- wood, wiring , etc...

My question is on filters. I have access to a large supply of high quality, free, 25x20x3 MERV 11 filters. Would these work with a lower quality prefilter? I know a MERV 14 would be better but Free is hard to pass up!

[Larry Edgerton]

Free are the best kind. I bought a box truck full of 20x25x4" industrial filters for $200, and that is what I use.

I did a lot of research on filtration when I was racing off road, and the most important factor in efficiency is reducing the vacuum on the inside of the filter. With a motor the only way was to increase filter area, but with the filter we are talking about you can not only increase filter area but reduce the speed of the blower as well. The less vacuum, the less chance that a particular size particle will be drawn through the filter medium which no matter what filter you are talking about is a series of holes.

Put your squirrel cage fan in the center of the unit so that it is drawing through the filters. I experimented and in my seriously large shop, the lowest speed of the fan did the best job, and would still clear out a cloud in minutes. As a bonus it will use less power. Its not a race to see how many times you can circulate the air, the objective is to catch the most and smallest particles. as far as I am concerned the little things they sell to hang on the ceiling are just too small, and have too little filter area to be of any real use in a busy shop. most squirrel cage fans I salvage are three speeds, just wire the speed and forget the variable speed control. One more thing to go wrong with no real benefit.

As to the "Catch the dust at the source" Bologna, that is all fine and well in a perfect world, but in reality fine dust just happens in a busy shop no matter what precautions you may take. The material comes in the door covered in dust. So having a ambient air filter makes the shop a better place to live, in my case that is close to the truth unfortunately.

I originally designed that filter because I wanted to paint my delivery van in the shop. I parked it underneath the filter and within minutes of starting the filter was gray, and when I was all done there was no gray paint on the floor. I lucked out the first time and got a winner.

I wired mine to come on with the lights, so if I was working, it was on. Filters would be vacuumed a couple of times and changed twice a year. Keep in mind that this is in a commercial shop, so as a hobbyist your filters will last much longer. Do not be excessive cleaning the filters, when they get a cake built up they are becoming even more efficient. You will hear a change in the sound of the squirrel cage fan when it needs cleaning or changing as it starts running at a higher speed due to not enough air movement.

Happy fabricating!

Larry
http://www.sawmillcreek.org/showthre...as-Air-Cleaner
I thought this was part of the other thread, the picture of my unit is in here:

[Keith Westfall]

I made mine from an old furnace blower fan and cage, and when I made the box for it, I designed it to use a double stack of furnace filters, and put them on two adjacent sides. Even though they are cheap filters - more is better - right? So i'm pulling air through 4 filters, and will sometimes when changing, bring the one from the inside to the outside and put the new ones on the inside.

Seems to work.