I tested air filters at my family's old company. I used 20 x 20 x 1
filters in a test stand. I used 800 CFM as a standart air flow, using a
flow hood to measure air flow and a damper to control it. A standard
fiberglass filter had a pressure drop of 0.75 to 0,8 inches water
column (IWC) at 800 CFM. all the 1" thick pleated filters that I tested
had a pressure drop of 0.2 Inches Water Column. That is 2-1/2 times as
much as a standard fiberglass filter! After being used in our HVAC
system for three months as recommended by the filter manufacturer, the
pressure drop on one of them was 0.35 IWC! I wrote an article about my
experience and it was published in the October 1999 issue of
Contracting Business Magazine. I can email you a copy of the article
if you can send me a copy of your email address that I can read.

Stretch
843-385-2220
O'Neill Bagwell Cooling & Heating
sixfoot7 @ sccoast . net