Understanding MERV Ratings

by Don Munn

Understanding MERV Ratings 4.75/5 (95.00%) 4 votes

MERV is an acronym which stands for, Minimum Efficiency Reporting Value. It is Standard 52.2 which was developed by ASHRAE (American Society of Heating Refrigerating, and Air Conditioning Engineers) in the late 1980s to determine the overall efficiency of media air filters. It is used to rate the ability of a filter to remove dust from the air as it passes through the filter. Higher MERV ratings mean fewer dust particles and other airborne contaminants pass through the filter.

These ratings are determined by adding particles of varying sizes, from .3 microns to 10 microns, into a controlled testing environment. The particles are added upstream of the test filter and a laser particle counter samples the air before it enters the filter and again after it leaves the filter. The two particle counts are compared to calculate the Particle Size Efficiency of the tested filter. Once this is determined, a MERV Parameters chart is used to determine the filters MERV rating.

MERV ratings range from 1 – 16 and measurements are in microns. Some of the common particles related to MERV ratings are pet dander, insecticide dust, smog, dust, viruses, wood, tobacco smoke, spores, bacteria and pollen.

Some of the most common filters found in residential use only have a merv rating of 1 to 4. These are typically disposable spun fiber panel filters and do not do a good job of filtering the air because they will not stop particles smaller than 10 microns.

Merv 5 to 8 rated filters are a better choice and are more commonly found in commercial applications. These filters will collect particles as small as 3 microns and are a good choice for home owners also.

Filters with a merv rating of 9 to 12 are used in commercial and industrial applications and will stop particles in the 1 to 3 micron range. These filters are a great choice for home owners who want the best dust control possible. When using filters with Merv 9 ratings and above it is important to clean or replace them when recommended by the manufacturer because they will have a negative effect on air flow when they become dirty. This can lead to performance problems and decreased operating efficiency of your heating and air conditioning equipment.

The most efficient filters have merv ratings of 13 to 16 and will stop particles as small as .3 microns. These filters are used in hospitals and other super clean environments. They are also very helpful in residential applications for those who suffer from allergies.

We hope you find valuable information in the table below. If you would like to read more about the different furnace filter options and some of the benefits of each, checkout the some of our other pages. Media Air Filters, Pleated Air Filters, HEPA Air Filters, Activated Carbon Air Filters

Electrostatic furnace filters are not listed in the table because they do not have MERV ratings. Arrestance and Resistance are terms more commonly used to rate electrostatic filters.

MERV Filter Efficiency Guide

Arrestance Efficiency MERV Rating Types Of Filters Tested Contaminant
60-80% < 20% 1 – 4 Disposable Panel Filters, Permanent Metal Filters, Fiberglass & Foam Media, Hogshair, Automatic Rolls Pollen, Spanish Moss, Dust Mites, Sanding & Spray Paint Dust, Textile & Carpet Fibers
80-90% < 20% 5 Pleated Panel Filters, Ring Panel Filters, Synthetic Media Pudding Mix, Snuff, Powdered Milk
90-95% 20-30% 6 Cube Filters, Self-Supported Filters Dusting Aids, Cement Dust
90-95% 25-30% 6-7 Pleated Filters Hair Spray, Fabric Protector
95-98% 40-50% 8 Pleated Filters, Ring Panel Filters, Extended Surface Pocket Filters Mold Spores
98% 50-60% 9-10 Extended Surface Pocket Filters Welding Fumes, Nebulizer Drops, Coal Dust, Auto Emissions
99% 60-70% 10-11 Pleated Panel Filters, Extended Surface Pocket Filters, Rigid Cell Filters Lead Dust, Milled Flour
99% 80-90% 12-14 Pleated MERV 12
Pleated MERV 13 Extended Surface Pocket Filters
Legionella, Humidifier Dust, Smoke, Copier Toner, Face Powder, Paint Pigments, Insecticide Dust
99% 90-95% 14-15 Extended Surface Pocket Filters, Rigid Cell Filters Sneeze, Cooking Oil
NA 95% 16 Rigid Cell Filters Bacteria, Tobacco Smoke

Don Munn About Don Munn
Don has been working in the HVAC industry for more than 25 years and shares his experience and knowledge on this site. If you find the information presented here helpful please use the buttons below and share with your friends.



{ 8 comments… read them below or add one }

Dave A.

My ultra efficient Lennox furnace has a Honeywell 16x 25x 4 filter element. MERV 11 . We do not have cats or dogs and our ducts were cleaned just before the Furnace was installed in 2010. Home Depot has Honeywell filters with a different rating system number of 10. Are they similar? (the 4 in dimension is actually 4.375, the others are 1/4 in. less.). Dave

Reply

Don Munn

I’n not sure about that Dave. I think Honeywell uses the MERV rating system like most filter manufactureres. As far as I know Filtrete is the only manufacturer that uses their own rating system.

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John Harper

I have a Lennox Conservator III G16 gas furnace no longer produced and live in Central Oregon that has a lot of volcanic dust. Currently I am using a 20 x 25 x 4″ filter with a 8 MERV rating which I change about 3 times per year. My questions are as follows:

!) How high a MERV rated filter can I use to trap more of the dust that ends up in my home?
2) If I increase my MERV rated filters to say 10, do I end up damaging my furnace? What about a MERV 12 rated filter?
3) What about your Nordic Pure MERV 12 filters (and their size?)?
3) Is there a trade-off point and if so, where is it?
Thank you very much for your time and consideration.

Reply

Don Munn

1) Unless the manufacturer recommends otherwise, there is no real restriction to what MERV rating you can use. But, it is important to remember that the higher the rating is the greater impact it will have on the operating efficiency of the equipment. Also, you may find it necessary to change the filter more often.

2) There is not a huge difference between a 10 and a 12 rating.

3) A Nordic Pure filter with a MERV 12 rating will basically be the same as any filter of the same rating of equal quality.

4) There is always a trade off when using filters with higher ratings and it is impossible to determine the point at which equipment efficiency is negatively impacted to the point that the gain in filter efficiency is not worth it. This is mostly due to system design and installation. A filter with a high rating will have a much greater impact on a system that is poorly designed and installed than one which is properly designed and installed.

There are many articles in how to section that will provide more information.

Reply

Ted Reem

Why do furnace manufacturers recommend a very low Merv number (2) in newer furnaces?

Reply

Don Munn

I’m not involved in that side of the industry but I think it probably has something to do with the fact that they are making these units so energy efficient. All equipment is designed to operate with a certain minimum air flow. In order for the equipment to operate at the rated efficiencies they require maximum air flows. A MERV 2 filter is not very efficient. Probably one of the cheap fiberglass type.

Also, furnaces have heat exchangers in them which are more sensitive to low air flow. Low air flow in a furnace can make the heat exchanger more susceptible to cracking under certain conditions.

Reply

Dianne Mader

Where to I find the Merv rating on my furnace filter? I currently am using DustStop. Thank you for our assistance,

Reply

Don Munn

Sometimes manufacturers stamp the MERV rating somewhere on the frame of the filter but this is more the exception rather than the rule. You should be able to get the information from the supplier or it may be listed on the filter packaging.

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