Informational Guide

MERV Rating Chart

The MERV rating chart explains the filter requirements of all applications in HVAC systems. We compare using it for AC units, furnaces & air purifiers.

by Ian Haynes

Air filters are among the most important yet commonly ignored components of a healthy functioning HVAC system. These lightweight barriers ensure that the indoor air remains fresh by blocking allergens, dust, and other pollutants from entering your property.

In addition to that, air filters improve your HVAC’s lifespan and reduce the need for frequent repairs.

However, not all air filters provide the same efficiency. Some air filters are drastically better than lower costing models, indicated by a MERV number.

But what is the MERV rating exactly? If you want to know, read on!

MERV (or Minimum Efficiency Reporting Value) ratings are numeric values given to filters for evaluating the PSE (particle size efficiency) of filter material. To put it simply, MERV rates the filter’s ability to catch and filter unwanted airborne-particles.

The PSE is the average particle-size captured by a filter after various filtration tests. Testing includes filtering different particle-sizes from larger particles like pollen or sawdust to tiny dust particles to measure the filter’s efficiency.

The higher the MERV ratings, the better and more effectively they strain out unwanted particles.

For instance, a 20 MERV rating filter can efficiently capture 100% of microscopic particles: carbon dust, smoke, and viruses. In contrast, filters with a 4 MERV rating can capture only 20% of dust mites, pollen, and other dust particles.

changing an AC filter

The MERV Rating Chart Explained

Most homeowners are unaware of this information, and many others find it hard to comprehend. However, we will untangle the complexities to help you make a better decision for your HVAC system.

Bigger Isn’t Always Better

The MERV rating chart delineates the filter requirements of all commercial and residential applications in HVAC systems. It thoroughly explains the complexities of varying filtering needs.

For instance, a hospital requires filters with higher MERV ratings than a residential air conditioner because of the importance of filtering bacteria from the controlled environment.

However, higher rating filters aren’t feasible in central air conditioning systems because of a large pressure drop.

Remember, choosing filters with appropriate MERV ratings is crucial for the health of people living in a building, plus the right filters also guarantee efficient HVAC operation.

Ranges Of MERV Ratings

The chart ranges from low (1) to high (20).

Filters with MERV ratings between 1 and 4 are termed as the lowest-rated and can filter larger particles like dust mites, carpet fibers, and pollen. On the other hand, filters with the highest MERV ratings, usually between 17 and 20, can filter carbon dust, smoke, sea salt, and viruses.

Filters with MERV ratings of 11 to 13 are suitable for places where cooking oil, smog, or tobacco smoke is present. Also, ratings between 8 and 11 are for areas rife with pet dander and hair spray fumes.

Pollen Vs. Bacteria

Simply put, the MERV rating chart offers useful information about filters that provide optimal protection against different types of pollutants. These pollutants are assessed in ranges between 0.3 to 10μm (micrometers).

Filters with less obstructive abilities can only block large particles and many commercial and residential applications are okay with it.

However, a tighter filter is essential to obstruct even the smallest particles such as bacteria, auto emission, or lead dust, especially for people suffering from asthma and areas where air should be kept clean, like laboratories.

Moreover, for areas contaminated with smoke and sea salt, you might need highly rated filters.

The Furnace Filters MERV Ratings: Usage Recommendation

With the help of MERV ratings, you can choose suitable filters for commercial, residential, or any other application.

These MERV ratings typically range from 1 to 20, with 20 being the highest and 1 being the lowest. If you want to know about various MERV ratings and their proper usage, read on!

MERV 1 to 4

Furnace filters having a 1-4 MERV rating provide minimal protection. These filters are flat and made-up of either synthetic materials or fiberglass.

They capture air particles at a minimum of 10μm and up. Cockroach debris, dust mites, pollen, carpet fibers, textile fibers, Spanish moss, spray-paint dust, and sanding dust are easy to deal with by this furnace filter.

These filters don’t last as long as higher-rated filters and do very little to improve air quality. Lastly, they are mostly used in residential air conditioning systems.

MERV 5-8

FilterBuy AFB MERV 8These medium quality furnace filters can obstruct anywhere from 20% to 70% particles between 3 and 10 microns (μm).

This includes mold spores, dust mites, pollen, sanding dust, pet dander, hair spray, fabric protector, dusting aids, cement dust, pudding mix, textile and carpet fibers, humidifier dust, coal dust, nebulizer dust, lead dust, and legionella.

According to EPA, filters with a minimum rating of 7 can be as efficient as HEPA filters in tackling hazardous pollutants.

They are made using cotton, polyester, or both and can also be used in better-equipped residential buildings, commercial buildings, hospital laboratories, industrial workplaces, and paint booths.

MERV 9-12

Aerostar 16x25x1 MERV 11These are some of the highest-quality furnace filters for residential properties, high-end commercial buildings, or hospital laboratories.

They can obstruct almost 90% of air-particles between 3 to 10 microns and about 70% of air-particles between 1 to 3 microns.

Additionally, they can block nebulizer drops, lead dust, milled flour, auto-emissions, welding fumes, humidifier dust, legionella, dust mites, pollen, textile, carpet fibers, coal dust, and cement dust.

This variant can help minimize or control allergy symptoms, asthma attacks, and COPD.

MERV 13-20

General surgery, care hospitals, high-end commercial buildings, carcinogenic materials, electronic and pharmaceutical manufacturers use these types of furnace filters.

They filter air particles measuring 0.3 microns or less. This includes viral droplets, carbon dust, sea salt, combustion smoke, bacteria, cooking oil, insecticide smoke, paint pigments, and face powder.

Residential systems, however, will need slight modifications to be able to use these types of furnace filters.

How To Determine MERV Ratings: The E1, E2, And E3 Particles

MERV ratings are determined by testing air filters using three different sized particle ranges: E1, E2, and E3.

E1 Particles

E1 particles are the smallest among the three different particle ranges tested by The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standards 52.2. These particles have a range between 0.3 and 1.0μm in diameter.

Typically, the air-particles that fall within this category are bacteria and smoke particles. Plus, E1 particles only cater to those furnace filters that have an 11 or greater MERV rating.

E2 Particles

E2 particles have a range of about 1.0 to 3.0μm in diameter. These particles usually include Escherichia coli (E.coli.) and pet dander (including dogs, birds, rodents, cats, and other animals with feathers or fur).

The PM2.5 particles – with 2.5μm or less – stay suspended for quite a long time and fall within the category of E2 particles.

Additionally, only furnace filters with MERV ratings of 8 or above are tested within this size-particle range.

E3 particles

Lastly, the E3 particles measure between 3.0 and 10.0μm in diameter. This size-particle range includes pollen, mold spores, and everyday dust. Almost all types of air filters can capture these particles to a certain degree.

However, higher-rated furnace filters can effectively block most E3 particles compared to those with low MERV ratings.

Differences Between MERV, MPR, And FPR

MERV, MPR, and FPR are the three applicable air-filter rating systems. They rate by size ranges and aren’t measured by the same organizations.

Firstly, MERV ratings range between a 1 and 20 scale, which denotes the effectiveness and efficiency of filters to catch specific air-particle sizes. It’s a nationally controlled and governed rating system established by ASHRAE and is the most widely used ratings for most US-based filter brands.

Secondly, the Microparticle Performance Rating (MPR) is formed by 3M. It rates air-filters’ ability to block size-particles between 0.3 and 1 microns. MPR ratings have a range from basic (300MPR) to premium (2800MPR). They’re commonly found in residential and commercial applications.

Lastly, the Filter Performance Rating (FPR) is formed by Home Depot. FPR ratings were set up to offer people an integrated ranking system; however, it features complicated measures. It rates a filter’s ability to block certain particles using a color code and a scale between 4 to 10 numbers.

Air Furnace Filter DIY

People Also Ask (FAQ)

What Is A HEPA Filter?

High-Efficiency Particular Air or HEPA filters are mechanical air filters that can remove 99.9% of particles such as pollen and dust bacteria with a size equal to 0.3μm.

What Is The MERV Rating For Smoke?

Typically, a 13 or higher MERV rating is ideal for a furnace filter to filter out finer smoke particles effectively.

What Is The MERV Rating I Should Use For My Home?

Every household in the US should use a minimal 8 MERV rating filter, which is sufficient to filter out most contaminants from indoor air.

Do Air Purifiers, Furnaces & Air Conditioners Use The Same Filters?

While it’s a misconception among most homeowners that air purifiers, furnaces, and air conditioning systems use different filters, this isn’t the case! You can use the same filter for all of them and save money, rather than purchasing separate filters.

Is The Higher The MERV Rating Better?

Its common knowledge that the higher the MERV rating, the better a filter will remove dust and other particles. However, remember to consider your HVAC system before purchasing to ensure efficient operation.

Why Shouldn’t I Use Cheap Furnace Filters?

They run the risk of getting sucked into the ventilation system. Also, a cheap furnace filter won’t be able to protect your HVAC or AC unit efficiently.

How Long Can You Go Without Changing The Air Filter?

Usually, you can go up to 30 to 60 days before having to install a new air filter.

What Happens If You Don’t Change The Air Filter In The Home?

It lowers the airflow to your AC/HVAC system and may push it to increase energy consumption.

Conclusion

To breathe clean, fresh air, it’s essential to have the right MERV rated air filters in your HVAC system or AC unit. Not only will they help you capture indoor pollutants, dust, allergens, and other particles, but they will also lower your utility bill and make your living environment healthier.

Ian Haynes

Ian Haynes is an HVAC writer, and researcher. He has worked on hundreds of articles relating to home cooling, heating and air quality with a vast knowledge of the technical aspects of these types of appliances. Outside of his work, Ian likes exploring Brooklyn with his Labrador. Learn more about the AC Lab team here.

Top