Flat Filters

( Fractional Efficiency of Several Air Cleaners
over the 0.01 --10µm Diameter Size Range)

Flat or panel filters usually contain a low packing density fibrous medium that can be dry or coated with a viscous substance such as oil to increase particle adhesion. Dry-type filter media may consist of open-cell foams, non-woven textile cloths, paper-like mats of glass or cellulose fibers, wood fill, animal hair or synthetic fibers. They may also consist of slit and expanded aluminum. Media filters of various materials are available in a wide range of sizes and thicknesses. The typical, low-efficiency furnace filter in many residential HVAC systems is a flat filter, one-half-inch to one-inch thick, that is efficient in collecting large particles, but removes a negligible percentage of smaller, respirable-size particles. Figure 4 demonstrates how the efficiency of the typical furnace filter over the 0.01 - 10 micron diameter size-range compares to other types of air cleaners which are described.