Understanding MERV air filter ratings for HVAC systems BY BOB JACKSON, CAFS, NCT PRESIDENT, NORSPEC FILTRATION LTD.
MERV ratings are used to rate the abili-
90 per cent, etc. This system was rela-
ty of an HVAC filter to remove contami-
tively easy to understand. However, it
An air filter’s performance is deter-
nants from the air as it passes through
had some major deficiencies in that it
mined by measuring the particle counts
the filter. Higher MERV ratings mean
did not provide a very good guide for
upstream and downstream of the filter
fewer dust particles and other airborne
selecting filters for particular contami-
being tested. Particle counts are taken
contaminants pass through the filter;
nants. In order to do that effectively, you
over the range of particles six times.
the
(Minimum
need to know two things – one, the par-
One begins with a clean filter and then
Efficiency Reporting Value), the higher
ticle size of the contaminant you are try-
uses that same filter five additional
the efficiency of an air filter.
ing to remove and two, the level of effi-
times.
higher
the
MERV
Obtaining the Data
Prior to the MERV rating system, air
ciency of the filter on that particle size.
The particle generator creates parti-
filters were tested according to a stan-
To better address those concerns, a new
cles of a known size in the air stream.
dard known as ASHRAE 52.1. This test
test standard known as ASHRAE 52.2
The objective is to create particles of
provided an average efficiency of the fil-
and the MERV rating system were
sufficient numbers to obtain meaningful
ter over its lifetime, and air filters were
developed to provide this particle size
counts in all of the measured particle
identified as a 30 per cent, 65 per cent,
efficiency data.
ranges which are the following:
Air Filtration Specialists 52 Ops Talk • Spring 2011
4704 - 91st Avenue Edmonton, AB T6B 2L1 Tel: 780-468-9296 Fax: 780-468-5806
