The information contained here is intended to help explain what a MERV Rating on Air Filters means to homeowners or commercial users of HVAC equipment.
As an Omaha HVAC contractor, we are frequently asked by our residential customers what MERV rating on air filters is best for use in the residential furnace. Commercial building owners or maintenance professionals also frequently ask us to provide MERV rating guidance for air filters used in their roof top HVAC equipment. Geothermal unit applications also are fitted with air filters.
Customers with allergies, other medical conditions, or with pets will often be interested in the better filtering capabilities that higher MERV rated filters can provide.
To start with, MERV is an acronym for Minimum Efficiency Reporting Value that was created in 1987 by ASHRAE. MERV is a standard that rates the overall effectiveness of air filters. Higher value MERV ratings equate to finer filtration, meaning fewer dust particles and other airborne contaminants can pass through the filter. The MERV rating in the current ASHRAE standard 52.2 is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass, with a MERV 16 filter capturing more than 95% of particles over the full range. A previous edition of the ASHRAE standard did list even higher MERV ratings in the range of 17 to 20, but they are absent in the current ASHRAE standard 52.2.
ASHRAE is an acronym for the American Society of Heating, Refrigerating and Air-Conditioning Engineers. ASHRAE was formed in 1959 by the merger of the American Society of Heating and Air-Conditioning Engineers (known as ASHAE) and the American Society of Refrigerating Engineers (ASRE). If acronyms are interesting to you, a few more relevant references that also have acronyms are provided at the end of this material.
The purpose of the ASHRAE Handbook (from which the MERV rating information came from) is to provide engineers, architects, and HVAC contractors with a useful and reliable reference data book relating to heating, ventilation, refrigeration, and air-conditioning.
The National Air Filter Association (NAFA) has developed application guidelines for the various MERV rated air filters. The NAFA is an international group of air filter distributors, manufacturers, and engineers. The NAFA guidelines are intended to assist homeowners and commercial users of HVAC equipment in their selection of the appropriate air filtration products and in understanding the various MERV ratings. The term arrestance is simply a measure of the ability of an air filtration device to remove synthetic dust from the air.
The table above contains data taken from the National Air Filter Association User’s Guide for ANSI/ASHRAE Standard 52.2-2012 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size dated November 2014 titled Understanding MERV. The data contained in the above table is intended to be a general guide to air filter use and does not address specific applications or individual air filter performance in a given application. Refer to manufacturer test results for additional information. Click here for a link to the NAFA website.
The video below discusses MERV ratings on air filters and also speaks to the differential pressure created by air filters. The higher MERV rated air filters produce higher differential pressure which can be problematic for HVAC systems.
For a good discussion on what air filter would be best, refer to this blog.
For a good discussion about upgrading your existing standard 1 inch filter to a more efficient 5 inch pleated air filter, refer to this blog.
For information on the description of Trane furnace model numbers, refer to this blog. For a description of Armstrong furnace model numbers, refer to this blog.
For tips on troubleshooting a gas valve failure, refer to this blog.
For technical material on troubleshooting a low voltage transformer failure, refer to this blog.
For information on how to properly connect the primary side of a low voltage transformer on roof top units, refer to this blog.
For a description of Trane roof top unit model numbers, refer to this blog.
For those wanting to perform further research into MERV ratings of air filters, the below organizations or documents may offer interesting insights.
ACGIH – the American Conference of Governmental Industrial Hygienists
AIA – the American Institute of Architects
AIHA – the American Industrial Hygiene Association
ASHRAE Handbook – standard 62.1-2016 Ventilation for Acceptable Indoor Air Quality
ASHRAE Handbook Standard 52.2-2017 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size
EPA – the US Environmental Protection Agency
NAFA – the National Air Filtration Association
NIOSH – the National Institute of Occupational Safety and Health