This article is from the Woodworking FAQ Collection 2, by multiple authors.
From: guido@twitch.UUCP ( G.Bertocci)
Date: 4 Jan 89 13:10:27 GMT
The most recent Workbench magazine recently had an article on dust
collection systems and they made a rather key mistake that
throws off most of computations in the article resulting in
grossly undersizing the requirements for a dust collector.
They used the max cfm and max static pressure numbers for dust collectors
together as in 500 cfm at 6 inches. The implication of this spec is that
system can move 500 cfm into a load of 6 inches.
These numbers are mutually exclusive. Max cfm is measured without any
load whatsoever while max static pressure is measured with the inlet
These specs should be read as pairs. For example, the above two
numbers would be 500 cfm @ 0 inches, and 0 cfm @ 6 inches.
Clearly what you want is all the points in between, but very few
manufactures provide this information.
Cincinnati Fan which makes many 2 stage dust collectors including the
Deltas has a pamphlet that includes plots of cfm vs length of
duct work of various diameters for different machines.
It is rather useful information.
I also went back and looked at Fine Woodworking articles on dust
collectors and they also make the same mistake of pairing
max cfm and max static pressure as a single point.
As a rather crude conclusion, if you are willing to move a dust collector
around and use less than 5-10 feet of duct work you can use a 3/4 - 1 hp
collector. If you want to centralize a permanent installation you need
a minimum 1 1/2 - 2 hp collector.
5 inch pipe is close to ideal for a home shop with only one machine
running at a time. You will get close to 500-550 cfm with a 2 hp machine.
4 inch pipe will also work, but you will limit the volume to about 350 cfm.