ASHRAE Journal - May 2013 - 85

MERV
Standard 52.2

Intended Dust
Spot Efﬁciency
Standard 52.1†

1 to 4

<20%

5 to 8

<20 to 60%

9 to 12

40 to 85%

13 to 16

70 to 98%

17 to 20*

Removed from Standard

Average Particle Size
Arrestance
Ranges
60 to 80%

>10.0 mm

Typical Applications

Typical Filter Type

Residential/Minimum; Light/
Commercial; Minimum/
Equipment Protection

Permanent/Self Charging (Passive);
Washable/Metal, Foam/Synthetics;
Disposable Panels; Fiberglass/Synthetics

Industrial Workplaces;
Pleated Filters; Extended Surface
Commercial; Better/Residential;
Filters; Media Panel Filters
Paint Booth/Finishing
Superior/Residential; Better/
Non-Supported/Pocket Filter/Rigid Box;
>90 to 98%
1 to 3 mm
Industrial Workplaces;
Rigid Cell/Cartridge
Better/Commercial Buildings
Smoke Removal; General Surgery;
Rigid Cell / Cartridge; Rigid Box/Non>95 to 99% 0.30 to 1 mm Hospitals & Health Care; Superior/
Supported/Pocket Filter
Commercial Buildings
80 to 95%

3 to 10 mm

Clean Rooms; High Risk Surgery;
Hazardous Materials

HEPA; ULPA

This table is intended to be a general guide to filter use and does not address specific applications or individual filter performance in a given application. Refer to manufacturer test results for additional information. *ASHRAE does not have a test procedure for HEPA testing and has dropped the MERV 17 to 20 classifications; †ANSI/ASHRAE
Standard 52.1 ranges are provided for reference only. Standard 52.1 was discontinued as of January 2009.

Table 2: Table 1 from NAFA User’s Guide for ANSI/ASHRAE Standard 52.2-2007.
May 2013

ASHRAE Journal

Source: American Cleanroom Systems

for leak-testing HEPA and ULPA ﬁlters in the
Maximum Particles/m3
Federal
factory as they are produced, at the job site
Standard 209E
Class
≥0.1 mm ≥0.2 mm ≥0.3 mm ≥0.5 mm
≥1 mm
≥5 mm
Equivalent
before they are installed, and after they are
ISO 1
10
2
installed in cleanrooms and in unidirectionalISO 2
100
24
10
4
ﬂow, clean-air devices. The scope further sugISO 3
1,000
237
102
35
8
Class1
gests that the RP be used to deﬁne the basis of
ISO 4
10,000
2,370
1,020
352
83
Class10
the speciﬁcation of HEPA and ULPA ﬁlters,
ISO 5
100,000 237,000 102,000
35,200
8,320
293
Class 100
and in the testing of unidirectional-flow,
ISO 6 1,000,000 237,000 102,000
35,200
8,320
2,930
Class1,000
clean-air devices and cleanrooms.
ISO 7
352,000
83,200
2,930 Class 10,000
ISO 8
3,520,000
832,000 29,300 Class 100,000
Selecting a ﬁlter to meet a certain MERV reISO 9
35,200,000 8,320,000 293,000
Room Air
quirement does not specify the maximum allowable leakage for a ﬁlter installed in a device and Table 1: ISO 14644-1 cleanroom standards.
by adding the requirement of IEST-RP-CC034.3
to a speciﬁcation, the design engineer has covered the maximum al- dropped in 2001 in favor of ISO 14664.
lowable leakage that is allowed in the test procedure. In most cases,
When calling for the required MERV on a project, the design
the air-distribution device will require an adequate seal or gasket, engineer should also state at which Standard 52.2-2012 velocifor example, a gel seal, to meet the minimum leakage requirements. ties the MERV is required. For example, the engineer can require
a MERV 15 at a velocity of 630 fpm (3.20 m/s).
Summary and Guidelines
HEPA and ULPA ﬁlters with MERV greater than 16 are no lonDesigners are required to comply with applicable county, ger addressed in Standard 52.2-2012. IEST-RP-CC001.5 outlines
state, or federal codes, and the IEST Recommended Practices the performance of HEPA and ULPA ﬁlters. The speciﬁcation of
covering HEPA and ULPA ﬁlters are often referred to in industry the required ﬁlter efﬁciency may not be met if the ﬁlter is installed
guidelines for the design of critical environmental spaces. For in a device. IEST-RP-CC034.3 covers deﬁnitions, equipment, and
example, the 2007 Minimum Design Standard for Health Care procedures for leak-testing HEPA and ULPA ﬁlters in the factory
Facilities in Michigan refers to IEST for ﬁlter testing that are as they are produced, at the job site before they are installed, and
not covered by Standard 52.2-2012. Note: Revised editions of after they are installed in cleanrooms and in unidirectional-ﬂow,
IEST-RP-CC001 and CC034 are expected to be published later clean-air devices. Units that meet this RP are typically provided
this year. Check for any changes in requirements.
with gel seals rather than gasket seals.
Engineers designing critical environmental applications
such as cleanroom and surgical suites may consider using the Acknowledgments
deﬁnitions as outlined in ISO 14644-1, the current recognized
The author would like to thank Don Bailey, P.E., senior mestandard for the classiﬁcation of cleanrooms (Table 1). Although chanical engineer, TLC Orlando, and R. Vijayakumar, Ph.D.,
it is common in our industry to classify rooms such as “Class with Aerﬁl for their contribution to this article.
100” or “Class 10,000,” this classiﬁcation system, originally
David A. John, P is general manager, vice president of ADE
.E.,
developed and maintained by the GSA FED-STD-209E, was Engineered Solutions of Florida, in Orlando, Fla.

ASHRAE Journal - May 2013

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