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Understanding MERV Ratings

Understanding MERV Ratings
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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

ArrestanceEfficiencyMERVTypes Of FiltersTested Contaminant
60-80%< 20%1 – 4Disposable Panel Filters, Permanent Metal Filters, Fiberglass & Foam Media, Hogshair, Automatic RollsPollen, Spanish Moss, Dust Mites, Sanding & Spray Paint Dust, Textile & Carpet Fibers
80-90%< 20%5Pleated Panel Filters, Ring Panel Filters, Synthetic MediaPudding Mix, Snuff, Powdered Milk
90-95%20-30%6Cube Filters, Self-Supported FiltersDusting Aids, Cement Dust
90-95%25-30%6-7Pleated FiltersHair Spray, Fabric Protector
95-98%40-50%8Pleated Filters, Ring Panel Filters, Extended Surface Pocket FiltersMold Spores
98%50-60%9-10Extended Surface Pocket FiltersWelding Fumes, Nebulizer Drops, Coal Dust, Auto Emissions
99%60-70%10-11Pleated Panel Filters, Extended Surface Pocket Filters, Rigid Cell FiltersLead Dust, Milled Flour
99%80-90%12-14Pleated MERV 12
Pleated MERV 13 Extended Surface Pocket Filters
Legionella, Humidifier Dust, Smoke, Copier Toner, Face Powder, Paint Pigments, Insecticide Dust
99%90-95%14-15Extended Surface Pocket Filters, Rigid Cell FiltersSneeze, Cooking Oil
NA95%16Rigid Cell FiltersBacteria, Tobacco Smoke

About the author: 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 share with your friends.

{ 13 comments… 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

    • 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.

  • 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.

    • 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.

  • Ted Reem

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

    • 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.

  • Dianne Mader

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

    • 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.

  • Kosmo

    Hi Don,

    I had a new furnace (American Standard Gold ZM) installed last year and I’m currently using the MERV 10 16x25x5″ filters the installed left me. Since I’m on the last one, I would like to understand my options what filters to get going forward. I found MERV 10, 11 and 8 filters in the 10x25x5″ (4 15/16″, actually) size and here is what I need help with: Are there issues if I go with MERV 8 filter (I wasn’t able to find any recommendations from Amercian Standard)? Is there a benefit to stay with the MERV 10 filters provided that I don’t see a difference in the air quality compared to the 1″ MERV 8 filters I was using with my old furnace? Since the price of the MERV 10 and the MERV 11 filters is almost identical (different manufactureres), is there a real benefit to go with MERV 11 if I cannot/shouldn’t go under MERV 10?

    Thank you for your help!

    • Don Munn

      Hi Kosmo,

      Other than removing smaller dust particles from the air, there is no benefit to using a MERV 10 filter instead of a MERV 8 and a MERV 11 filter is only slightly better than a filter with a MERV 10 rating.

      The only reason to use a filter with a higher rating is to remove more dust from the air. If you don’t have allergies and dust is not an issue I see no reason for you to use a higher rated filter. They are more expensive and need to be changed more often than filters with smaller ratings such as MERV 7 and 8.

  • Mark Eden

    I have a large Lennox gas furnace and AC air handler set up with Honeywell control on 3 zones. The unit is about 20 years old but still works great. The former homeowner had removed to electronic air filter and replaced it with a 20x24x4 pleated filter that seems to work fine . The A coil is very clean.

    My question: The cavity where the filter sets is big enough to go with a 6 inch filter.
    (The current 4 inch requires a couple of shims) Would it be a benefit to go to the 6 inch over the 4 inch. Considering the increased cost of the 6 inch over the 4 in?

    We do have 2 large dogs and I smoke cigars in one room that is serviced by this same unit. Home is 3000 sq ft. This smoking room (my man cave) Is well ventilated while smoking and I run a free standing air cleaner in this room.

    Thank you!

    • Don Munn

      Hey Mark,

      The only real advantage to using a 6 inch pleated filter over a 4 inch pleated filter is how long it can remain in the system. Because the filter surface area is much larger the dust loading capacity of the 6 inch filter will be about 50% more than the 4 inch filter so you will be able to leave it in the system for a longer period of time.

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