ASHRAE Journal - November 2019 - 76

COLUMN IEQ APPLICATIONS
Jeffrey Siegel

Residential Filtration
BY JEFFREY SIEGEL, PH.D., MEMBER ASHRAE

Residential ﬁltration has always been the neglected sibling when compared to
commercial ﬁltration. Filter standards are usually based around commercial uses and
HVAC systems. However, residential ﬁlters experience very different conditions than
commercial ﬁlters. Some of these differences include lower average ﬂow rates, system
operation (thermostatic cycling vs. continuous), and a much higher fraction of recirculating systems rather than systems with mechanical outdoor air ventilation.
There are also some fundamental differences in context: commercial ﬁlters are largely changed according
to a contract by a professional on a ﬁxed schedule rather
than by a homeowner who likely changes the ﬁlter when
they remember and may select a ﬁlter based on factors
other than performance.
Residential systems are often smaller and they are
much less standardized, which can lead to important
differences for ﬁltration. Although there have been
many studies of residential ﬁltration, most are relatively
short-term and only some have characterized the buildings and systems. As a result, the ﬁltration community
lacks long-term data to make recommendations to
homeowners about ﬁlters.
When we embarked on the ﬁeldwork for ASHRAE
Research Project RP-1649: Indoor Air Quality and Energy
Implications of Filters in Residential Buildings, I anticipated
that we would ﬁnd that higher efﬁciency ﬁlters performed better than low efﬁciency ﬁlters and I also
anticipated some variation in performance for the same
ﬁlter in different homes. To a certain extent, this is
what we found, but the story that emerged was almost
entirely one of variation. The same ﬁlter performed very
differently in different homes and in some cases, high
efﬁciency and lower efﬁciency ﬁlters performed surprisingly similarly in the same home. The project thus
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became largely about exploring this variation and trying
to understand what it means for ﬁltration use and ﬁlter
standards in residences.

Methods
The project monitoring subcommittee selected four
ﬁlters: a MERV 8 uncharged ﬁlter and MERV 8, 11, and 14
electret ﬁlters (hereafter called MERV 8E, 11E, and 14E),
all in a 1 in. thickness. We found 20 homes in Toronto
that were willing to tolerate frequent visits and continuous monitoring of their HVAC systems and particle concentrations in their living room for one year. The homes
were mostly single-family residences in central Toronto,
two were units in high-rise condominiums and one was
a unit in a large home converted into smaller apartments. All had forced-air systems, all but one without
mechanical ventilation (outdoor air), and all provided
both heating and cooling. We installed each ﬁlter for
three months in a random order in each home to allow
us to compare the performance of different ﬁlters across
the study without seasonal or other biases.
The measurements for the project included both
short-term measures of ﬁlter efﬁciency, effectiveness,
airﬂow, and ﬁlter pressure drop at the beginning,
Jeffrey Siegel is a professor in the Department of Civil and Mineral Engineering at the
University of Toronto.

ASHRAE Journal - November 2019

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