MERV, or Minimum-Efficiency Reporting Value, is a measure of the efficiency with which filters remove particles of specific sizes.
According to the Standard 52.2 application guidelines, particles in this size range include pollen, dust mites,
mold spores, hair spray, powdered milk, and, of course, snuff. Higher
MERV ratings (from 13 to 16) are needed to remove bacteria and smoke
particles. At the top of the scale are HEPA filters with MERV ratings
from 17 to 20, which can filter out particles smaller than 0.3 microns,
including some viruses.
It stands to reason that the ability to filter smaller particles would come with the penalty of increased resistance
to air flow. Could the shift to better filters mean that they could
cause problems with inadequate air flow or greater fan energy use? Are
all high-MERV filters equal, or do some have less pressure drop than
others? How much better are 2-inch and 4-inch-thick pleated filters than
1-inch filters? Are larger ducts required to offset the added pressure
drop of the filter? With a pat on the back from our Building America
program sponsors, my colleagues and I at Davis Energy Group, in Davis,
California, decided to run some tests to answer these questions.
Read David Springer's article in the November/December, 2009 issue of Home Energy.