Taking the Confusion Out of Air Filter Efficiency or What Do They Really Mean When They Say That?

I will try to keep this simple and short so as not to add to some of the confusion over air filter efficiencies. First, I would like to point out that any company that sells an air filter that states an efficiency rating without basing it on a particle size is providing you with basically useless information. For example: an air filter that has a statement reading “this filter will remove up to 95% of all airborne contaminants in your home or office”, doesn’t really tell you anything. Since most of the respirable particles that actually are harmful are usually less than 2 microns in size, don’t you think it would be important to tell you what size particles they actually remove from the air? So, let’s look at this statement again. “95% of all airborne contaminants” sounds pretty good, doesn’t it? Our HEPA air filters remove 99.97% of all airborne contaminants at 0.3 microns and smaller. At first glance these two air filters look similar in capability. But the first air filter provides no particle size range or efficiency based on particle size.

Recently the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and the air filter industry have come up with a standardized rating system, based on the European concept, of a MERV rating for each type of air filter. This numbering system makes it easier to evaluate and compare mechanical air filters and will hopefully eliminate some of the confusion regarding the overall effectiveness of any type of a mechanical air filter on removing airborne particulates, especially those that are less than 2 microns in size.

Bbelow you will see the new MERV ratings. This MERV rating chart has the MERV ratings, 1-16 on the left hand column and then there are five other columns showing the average efficiency in microns, average arrestance and the final resistance as measured in inches of water. Most companies that make air filters are now using this MERV rating, so you will see a MERV number on the air filter and perhaps some rated efficiency.

Comparing Various Air Filters to MERV Ratings

• Throw-Away Fiberglass Media MERV 1 -MERV 4
• Pleated Media Air Filters 30% ASHRAE MERV 10 – MERV 11
• Pleated Media Air Filters 65% ASHRAE MERV 13 *
• (* 65% ASHRAE is about 20% effective on less than 1 micron particles)
• Pleated Media Air Filters 95% ASHRAE MERV 14

Some of the man-made synthetic media like that used in the 3M Filtrete air filters may be rated MERV 15. However, they hold very little dust and load up quickly and have a relatively high-pressure drop (static pressure) and can affect the performance of the heating / cooling system.

MERV Ratings Comparison Chart

RESPA Air Filter Efficiency – MERV Rating Chart

IMPORTANT NOTES:It is important that you select the RESPA Filter that best fits your application.MERV is an acronym for “Minimum Efficiency Reporting Value”. The MERV rating on an air filter describes its efficiency as a means of reducing the level of 3 to 10 micron-sized particles in air which passes through the filter. Higher “MERV” means higher filter efficiency. The purpose of the MERV standard is to permit an “apples to apples” comparison of the filtering efficiency of various air filters. <Read more about MERV and HEPA filter ratings>HEPA air filters are not MERV rated as they exceed the ASHRAE test protocol 52.2 used in determining the MERV ratings. In fact, HEPA air filters are the ONLY mechanical air filters that are tested and certified to meet a specific efficiency at a specific particle size. All HEPA air filters must meet a minimum efficiency of 99.97% at 0.3 microns. <Read more about MERV and HEPA filter ratings> Comparison of EU Standards to ASHRAE 52.1, 52.2 (MERV Ratings) Considerable differences exist between filter ratings in North America and Europe. This article helps the reader to understand the differences between ASHREA and EU standards for Filtration. Additional light is shed on the significant differences in the HEPA filtration standards between the US Government and the European standards. This article will help the reader to appreciate the MERV 16 filtration offered by Sy-Klone International. <Read more about European filter standards and how they compare to MERV ratings> >> Go to RESPA-SD Product Information >> Go to RESPA-SDX Product Information

RESPA Filter Model European Filter Rating Efficiency Standard 52.5 Minimum Efficiency Reporting Value (MERV) Dust Spot Efficiency Arrestance Typical Controlled Contaminant Typical Applications and Limitations Typical Air Filter/Cleaner Type HEPA Filter*  (FEFF004 for RESPA-SD/SDX)Recommended when the very highest level of filtration is needed, or where HEPA filters are required by regulatory requirements. n/a n/a n/a 0.30 micron particle size: • All Combustion smoke • Radon Progeny • Sea Salt • Carbon Dust • Orthopedic Surgery • Carcinogenic Materials >99.97% eff. on .30 pm Particles MERV 16 Filter* (FEFF005 for RESPA-SD/SDX)Covers all uses that require up to MERV 16 rating. Recommended for uses where airborne contaminants place operator at risk, including contaminants such as Diesel Particulate Matter and Respirable Silica. We highly recommend this filter as it represents the best mix of high efficiency filtration, operator protection and economy. EU P3** (~16+) n/a n/a .30-1.0 micron Particle Size • All Bacteria • Most Tobacco Smoke • Proplet Nuceli (Sneeze) • General Surgery • Hospital Inpatient Care • Smoking Lounges • Superior Commercial Buildings Bag Filter – Nonsupported microfine fiberglass or synthetic media, 12-36 in. deep, 6-12 pocketsBox Filter– Rigid Style Cartridge, Filters 6 to 12″ deep may use lofted or paper media 16 n/a n/a 15 >95% n/a 14 90-95% >98% 13 89-90% >98% 12 70-75% >95% 1.0-3.0 micron Particle Size: • Legionella Humidifier Dust • Lead Dust • Milled Flour • Auto Emissions • Welding Fumes • Superior Residential • Better Commercial Buildings • Hospital Laboratories Bag Filter – Nonsupported microfine fiberglass or synthetic media, 12-36 in. deep, 6-12 pocketsBox Filter– Rigid Style Cartridge, Filters 6 to 12″ deep may use lofted or paper media 11 60-65% >95% EU P2** 10 50-55% >95% 9 40-45% >90% MERV 8 Filter* (FEFF003 for RESPA-SD/SDX)Covers all uses that require up to MERV 8 rating. Recommended for non-human respiratory environments, such as electrical compartments. 8 30-35% >90% 3.0-10.0 micron Particle Size: • Mold Spores • Hair Spray • Fabric Protector • Dusting Aids • Cement Dust • Pudding Mix • Commercial Buildings • Better Residential • Industrial Workplace • Paint Booth Inlet Pleated Filters – Disposable, extended surface area, thick with cotton-polyester blend media, cardboard frameCartridge Filters– Graded density viscous coated cube or pocket filters, synthetic mediaThrowaway– Disposable synthetic panel filter. 7 25-30% >90% 6 <20% 85-90% EU P1** 5 <20% 80-85% 4 <20% 75-80% >10.0 micron Particle Size: • Pollen • Dust Mites • Sanding Dust • Spray Paint Dust • Textile Fibers • Carpet Fibers • Minimal Filtration • Residential • Window A/C Units Throwaway – Disposable fiberglass or synthetic panel filter.Washable– Aluminum MeshElectrostatic – Self charging woven panel filter. 3 <20% 70-75% 2 <20% 65-70% 1 <20% <65%

This is an important chart to keep for future reference in determining the best filter style and type for your specific application. Understand that the higher the MERV rating the greater the resistance or static pressure will be across the filter media. For most HVAC furnace filter applications a MERV 8 and lower since these filters will allow for lower resistance with good filtration of larger particles.  Using the 3M type filtrete filter not recommended for most general duty residential heating/cooling systems. These filters load up very quickly and will actually reduce the HVAC fan performance requiring longer cycles to both heat and cool your home.

Pure Air Systems has been manufacturing commercial grade HEPA and Carbon based air filtration systems since 1985. These units are designed to be used either attached to existing ducted HVAC systems or as stand-alone units. The ability to use a true HEPA filter system ( which would have a MERV rating of 18 if they rated them) in a residential application makes these unit unique in the filter market.

For more information on the complete line of HEPA and Carbon based air filtration systems please go to our website at: www.pureairsystems.com or follow us on Twitter @pureairsystems and like us on Facebook. Of course you can always call us on our toll-free number at: 800-869-8025.