Pick the right filter
CONTAMINANT’S vs. REQUIRED AIR EXCHANGE RATE
Nuisance dust lint – 15 minutes (4 ACH)
Light odor, chemical – 10 minutes (6 ACH)
Moderate odor, chemical, tobacco smoke – 8 minutes (8 ACH)
Heavy odor, chemical, tobacco smoke – 6 minutes (10 ACH)
To determine room volume: Volume = length X width X
ASHRAE Standard 52.1-1992 is used to measure the performance
of most filters used in HVAC systems and air cleaning systems. Besides measuring air flow resistance,two filtration
performance measurements can be made depending on the type of filter. The dust weight arrestance test indicates
how well a filter captures larger,heavier particles (greater than 10 microns). It is used to evaluate panel filters
used in HVAC systems and as prefilters in air cleaners. These filters usually are not very effective on fine dusts
and smokes. It is usually used to elevate pleated filters, bag filters and electronic filters. Military standards
282(not an ASHRAE standard) measures the percentage removal of 0.3 micron particles of D.O.P smoke. These are very
high efficiency filters. A high-effiency particulate air filter (HEPA) is 99.97% effcient using this test. By comparison,
a 95% dust spot filter is about 65% D.O.P.
Prefilters are used in air cleaners to filter lint, dust, and other large particles. Usually a flat panel or a
1/2 inch pleat is used. Minimal performance should be at 80-90% arrestance. Better prefilters are at least 30%
dust spot efficient. Frequent changing of disposables or cleaning of reusable filters prolongs the life of the
The main filter removes fine particulates. The minimum efficiency should be 60% dust spot. If tobacco smoke is
a concern, the minimum efficiency should be 95% dust spot. Special air cleaning requirements may call for a 95%
D.O.P. or 99.97% D.O.P. HEPA filter.
Final filters are used when a high level of air cleanliness is required. Often a 95%-99.99% D.O.P. filter is used
after a 60%-95% dust spot fliter. This configuration protects the more costly final filter.
Absorbent filters are used to remove odors, chemical vapors and gases. No mechanical or electronic filter can remove
The absorbent material most often used is activated carbon or charcoal. It is capable of removing over 200 different
odors, vapors, or gases. Carbon is primarily used to filter organic odors, solvents, volatile organic compounds
(VOCs), and tobacco smoke. Carbon filters are available in three types:
Polyester pad (1/4"-3/8" thick) with carbon powder bonded to the fibers. for light to medium duty filtration.
May also be used as a prefilter.
Carbon web (1"-2" thick) has carbon granules suspended in a non-woven matrix. Good for medium duty requirements
and where high air flows are needed.
Granular carbon panels and cells are available in 1" and 2" depths. They are used for relatively high
contamination levels or when longer filter life is desired. However, these filters are restrictive to air flow.
Potassium Permanganate is used for gases and vapors like formaldehyde, hydrogen sulfide, and sulfer doixide. It
is impregnated in small alumina spheres. The contaminant is absorbed onto the sphere and chemically reacts with
the potassium permanganate. New unexposed spheres are purple. As reaction take place, they turn gray or brown.
When all the spheres have changed color, they are no longer active and cannot remove the contaminant.
Zeolite is a natural mineral which absorbs ammonia and
Type 5 is a proprietary material which absorbs and chemically reacts with acid vapors, chlorine, fluorine, bromine
and iodine. Color changes from yellow to white.