Save $350 and your lungs -- so easy!!

[ken cierp]

I can't be the first to think of this air filtration idea -- I am tired of paying about $50 every time my big honking Delta air cleaners need filters. I got to analyzing exactly what that piece of equipment was actually doing -- and that is sucking air through a couple of fabric or electrostatic filters which BTW are not HEPA grade. Top CFM is 1200. Plus the thing weighs a ton and at high speed I don't like the whiny noise it makes. So I look up the CFM specs of the $16 Lasko 20 x 20 box fan --- over 2500!!! And they are very quite -- to the design board -- here's what I came up with -- works great, I use MERV 12 furnace filters ($4.50 ea) which do perform on a par with HEPA -- so effective that when I tested the flow with a smoldering piece of wood the smoke odor was gone. I made room for a pre-filter not sure its necessary. I wanted the unit to be very light so its made of CB and foam with wood framing. Pretty cool I am going to make a couple more -- even thinking about possibly offering a kit.

[Tim Benware]

Interesting Ken. When I was spraying water base lacquer in my tear down spray booth I did the same thing (sorta). My box was smaller and only had one filter but suited its purpose. I bought a used Wood River air cleaner and within 2 weeks the electronics went so I hook it up to power single speed and use cut down regular filters. Should have done what you did.

[Dave Bagwill]

I like it.

[peter havriluk]

That is just so damned smart!

[ken cierp]

I should note that the filters are taped like hinges and care has to be taken to get the direction of flow correct. The location stops (made of wood) are hot glued to the pink foam top and bottom. In the perfect world the stops could be made of soft foam to provide a better seal. The lid is held in place with Velcro. This configuration has 2000 sq. inches of filter surface the Delta has 1728 sq. inches. If you wanted something a little smaller you could adjust the filter size to say, 16 x 20 or 12 x 20 etc.

[John Link]

Is there any reason against mounting the filters parallel to each other, successively - so that the first one catches most of the dust and therefore would tend to be the one that got changed most of the time?

[ken cierp]

You want lots of surface area so it allows free air movement -- the pre-filter could and should have a lower MERV rating (more porous) to capture the largest particles (same as my Delta). I just copied how these things are made commercially. I don't think the "strainer" concept has any advantages and would greatly reduce CFM as well the potential to overload the fan motor. If you look at a 2 or 4 inch thick furnace filter its still a bunch of longer folds -- more surface area.