Understanding MERV - NAFA User’s Guide for ANSI/ASHRAE Standard 52.2-2012

Oct 12, 2026

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Understanding MERV explains how the NAFA User’s Guide helps end users and specifiers select air filtration products and interpret MERV values from ANSI/ASHRAE Standard 52.2-2012. It summarizes improvements over Standard 52.1, clarifies how dust holding capacity should not be used for life calculations, and provides application guidance mapping MERV ranges to efficiency, arrestance, particle-size ranges, and typical filter types. It also describes the 52.2 test method for obtaining particle-count data across size ranges and test cycles, culminating in composite minimum efficiency curves.

LanguageEnglish

CategoryPaper Templates

FormatPDF

Pages2

Reading Time1 min

AccessFree to download

Introduction

ANSI/ASHRAE Standard 52.2 Improvements

Table 1: Application Guidelines

Standard 52.2 Test Procedure: How Data Is Obtained

Accreditations: NAFA Certified Air Filter Specialist (CAFS) NAFA Certified Technician (NCT) Level I and Level II NAFA Certified Products (NPC) Publications: Air Media NAFA Guide to Air Filtration Installation Operation and Maintenance of Air Filtration Systems (IOM) National Air Filtration Association􀂣 PO Box 68639 • Virginia Beach, VA 23471 (757) 313-7400 • Fax (757) 313.7401 [www.nafahq.org](www.nafahq.org) • email: [nafa@nafahq.org](nafa@nafahq.org) November 2014 Understanding MERV NAFA􀂣 User’s Guide for ANSI/ASHRAE Standard 52.2-2012 Method of Testing General Ventilation Air-Cleaning Devices for Removal Eff iciency by Particle Size INTRODUCTION This ANSI/ASHRAE Standard 52.2 "Understanding MERV" User Guide was created by the National Air Filtration Association (NAFA), an international group of air filter distributors, manufacturers and engineers. This Guide, and the application of a particle-based contaminant removal standard prescribed by ANSI/ ASHRAE Standard 52.2-2012 “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size,” are intended to assist endusers and specifiers in their selection of appropriate air filtration products and understanding of the MERV values in the 52.2 test reporting. ANSI/ASHRAE STANDARD 52.2 ANSI/ASHRAE Standard 52.2 features many improvements over the 52.1 standard. In 2009 ANSI/ ASHRAE 52.1 "Dust Spot" efficiency testing was removed from the standards while two other parts of the 52.1 Standard were adopted into the 52.2 Standard, allowing for the 52.1 to be retired. The two parts of 52.1 adopted by 52.2 are "Arrestance" for determining MERV 1-4 and "Dust Holding Capacity."It should be noted that the ANSI/ASHRAE standard makes it clear that Dust Holding Capacity is reported as the total weight of synthetic loading dust captured by the air cleaning device over all of the incremental dust loading steps. This value should not be used to calculate the expected life of the device in use. TABLE 1: APPLICATION GUIDELINES | MERV Std 52.2 | Intended Dust
Spot Efficiency
Std 52.1 (2) | Average
Arrestance | Particle Size
Ranges | Typical
Applications | Typical
Filter Type | | --- | --- | --- | --- | --- | --- | | 1-4 | <20% | 60 to 80% | > 10.0 µm | Residential/Minimum Light Commercial/ Minimum Minimum Equipment Protection | Permanent / Self Charging (passive) Washable / Metal, Foam / Synthetics
Disposable Panels Fiberglass / Synthetics | | 5-8 | <20 to 60% | 80 to 95% | 3.0-10.0 µm | Industrial Workplaces Commercial
Better / Residential Paint Booth / Finishing | Pleated Filters Extended Surface Filters Media Panel Filters | | 9-12 | 40 to 85% | >90 to 98% | 1.0-3.0 µm | Superior/Residential Better/Industrial Workplaces Better/Commercial Buildings | Non-Supported / Pocket Filter / Rigid Box
Rigid Cell / Cartridge
V-Cells | | 13-16 | 70-98% | >95 to 99% | 0.30-1.0 µm | Smoke Removal General Surgery Hospitals & HealthCare Superior/ Commercial Buildings | Rigid Cell / Cartridge Rigid Box / Non-Supported / Pocket Filter
V-Cells | | MERV Std 52.2 | Efficiency | | | Typical
Applications | Typical
Filter Type | | 17-201
Deleted from ASHRAE | 99.97%-99.9999% | | | Hospital Surgery Suites Cleanrooms Hazardous Biological Contaminants Nuclear Material | HEPA
ULPA | Note: 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. (1) ASHRAE does not have a test procedure for HEPA testing and has thus dropped the MERV 17-20 classifications. (2) ANSI/ASHRAE 52.1 ranges are provided for reference only. The ANSI/ASHRAE 52.1 Standard was discontinued as of January 2009. Some of the improvements found in the ANSI/ASHRAE 52.2 standard include: • The use of mandatory (code) language, which enables the standard to be reference

FAQs

What is the purpose of the ANSI/ASHRAE Standard 52.2 "Understanding MERV" user guide?

It assists end users and specifiers in selecting appropriate air filtration products and understanding MERV values reported under Standard 52.2-2012. It links the particle-based contaminant removal standard to practical product selection and reporting.

How does Standard 52.2 improve on Standard 52.1?

It removes the 52.1 "Dust Spot" efficiency testing and adopts two elements into 52.2. It also expresses efficiency as a function of specific particle size and reduces 72 data points into a single minimum-efficiency curve.

How is filtration efficiency determined in the Standard 52.2 test procedure?

Particle counts are measured upstream and downstream over twelve required particle-size ranges across six test cycles. Filtration efficiency is calculated as the downstream-to-upstream ratio for each measurement, with the lowest values used to define the composite minimum efficiency curve.

Oct 12, 2026

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