Home Articles Resources Archives Mailing Lists Classifieds


Classes of Air Filters

by an author who asks to be anonymous
March 1997

As someone who has spent five thousand dollars on air cleaners/filters/ whatever over the past five years, here's a bit of advice:

If you know exactly what you need to take out of the air, it is fairly easy to choose the right filter to get it, if one exists. If you are trying air cleaners at random to try to find one that helps more than it hurts, you will spend a lot of money and may get nothing for it. Try the cheap ones first, and know the upside and downside of each before trying it!

Classes of air filters:

Furnace filter: takes out the bigger particles. Best of these I've found is 3M Filtrete, but it costs close to 20 times as much as a cheap one. Replacing the cheap one five times as often would be better for someone dealing with very large particles. Dasun "final filter" is a unique alternative here.

HEPA: takes out particles down to 0.3 micron. Some pretty good ones at discount stores like Target. Noisy. Bought one with a plastic housing that offgassed intolerably. If the problem is particles smaller than 0.3 micron, these will stir up more than they take out of the air. Note that the electronics industry has more advanced HEPA-type materials good to 5 9's at 0.12 micron; there are hospital-ICU-room filter vendors who can substitute these filters -- but at 10-20 times the price of a normal HEPA.

Carbon: takes some VOCs (volatile organic chemicals) out of the air. Used as prefilter on some HEPAs. An advanced topic here is to use a bed of something like Purafil, but don't know of an off-the-shelf version of this other than the Dasun zeolite bags.

Ionizers/Electrostatic filters: Idea is to get particles out of the air and stuck to something using electricity. Cheap ionizers just throw it onto the nearest wall. The Clearveil unit I mentioned seems to keep it all inside on the collection paper. These all produce some ozone, which is a downside.

Oxidizers: ozone generators, "Second Wind" units, etc: attack both VOCs and particles which can be rendered harmless by oxidation. Quite useful on some things, useless on others. Downside is the effect of ozone on people; either turn it off 15 min before anyone comes in or use a "Second Wind" intermittently on a low setting.

UV-C light: kills germs when used appropriately, not for amateurs like me -- damages the eyes, need to get it intense enough to work at given duct dimensions and air flow rate...

(I am a customer of but have no interest in the devices mentioned here, cos who make them, or distributors.)

This article is copyrighted. No reprints without permission

Home Articles Resources Archives Mailing Lists Classifieds

Cyndi Norwitz / webmaster@immuneweb.org / Last Modified: 1/25/98