Kate Hudson (X) Jan 10, 2007:

here is an explanation of what change-out pressure is Filter replacement
It is important to replace filters frequently. Pleated filters will load up with lint and dust
more quickly than lint filters. This buildup reduces the amount of air circulated by the
ventilation system. Inadequate air flow means less air supply to dilute objectionable air
particles, and less return air to remove such particles. How quickly a filter bank loads up
depends on the efficiency of the filter, how many particles there are in the air, and the
amount of air that passes through the filter.
A filter gauge installed across a filter bank indicates the pressure drop across the filter in
inches of water column (" W.C.). The pressure drop observed when new filters are installed
is called the clean pressure drop. For pleated filters this is usually about 0.25" W.C. As the
filter loads up, the pressure drop will increase. The filter is usually replaced when the
pressure drop increases by about 0.2" W.C. This is called the changeout pressure.
A filter gauge is the most effective way to track filter loading. Unfortunately, many filter
banks do not include a filter gauge. In the absence of a filter gauge, the filters should be
checked visually every month, and replaced when they are evenly coated with dust.
When a new set of filters is installed, the replacement date should be written on the
cardboard filter frame. This will help determine the average life of the filters.
This information is available at our website: www.nationaltbcenter.edu
What type of air filter should I use in my building’s ventilation system?