I just finished my own shop-built air cleaner.
A friend in the heating / cooling business gave me a used furnace blower of
unspecified, but generous, capacity. It's outlet is about 12" x 15". I built
a box around it with a 2-by frame to keep the filters from being sucked into
the blower and to give the air some mixing room inside the box. I also
wanted to leave the possibilty of using the back for filtration area open in
case the side openings were too restrictive. I have a three layer filter.
The first filter layer is the 56 cent spun fiberglass variety to keep out
large bugs / small birds. The second stage filters to 7 microns and the
third stage filters to .3 microns (about .000012" -- filters bacteria and
molds, some viruses). I used a total of six filters on each side (2, 20"x20"
filters taped into a 20"x40" rectangle per layer) giving 20 x 40" outside
filtering surface on each side (800 sq inches, not counting pleating) for a
total of 1600 sq inches exposed filter surface.
That's clear as mud.
I ended up with two filters, 20"x40"x3" with a coarse outer layer and a .3
micron final layer sandwiched around a 7 micron pleated filter. Each filter
is thus 800 sq inches for a total external filtering area of 1,600 sq
inches. The intake is on the sides and the exhaust is out the front. There
is a doubled layer of 1/2" plywood for a top to which are mounted my belt
sander, grinder and task light. The whole arrangement is about 40" wide by
40" tall by 24" deep. I'll probably put some hardware cloth in front of the
exhaust to keep the safety harpies at bay.
My shop is 11' by 31'. (About 1/2 my basement.)
I exhaust the air lengthwise across the middle of the floor. At the far end,
it raises up and follows the outside walls to return ... carrying dust away
from my face. My HF 2 hp chunk collector bleeds 30 micron dust but is
between me and the air cleaner along the outside wall. It's really nice to
fetch the DC bags a whack and see the dust immediately head for the air
Cost to build? Approx. $40. I used salvaged dunnage plywood and 2x2's for
the casing, glue & drywall screws to hold it together, a slap of old paint
to spruce it up and salvaged wiring parts. About $38 of the cost went into
the filters and I can feel the strong breeze all the way to the back wall.
Sawdust and lathe shavings still fall to the floor ... but there doesn't
seem to be any dust anywhere anymore. Even when the DC is turned off, I
leave the air cleaner running.
FWIW ... I still wear my respirator ... I'm down to my last pair of lungs.