What Is A MERV Rating? a helpful 101 course

If you’ve ever gone shopping for an air filter, chances are you’ve seen a couple of different numbers and ratings. At least one set of these numbers is the MERV rating, which the majority of air filters have. 

MERV ratings are how air filters are scored based on their ability to clean the air and capture particles of varying sizes. The MERV rating is a globally recognized system that provides customers with an easy-to-read quality and performance rating between 1 – 16.

Filters with superior performance are rated higher. They also demonstrate a proven ability to remove particles of smaller sizes, such as dust or other allergens. Keep reading to learn more about MERV ratings and why they’re important.

MERV Rating 101: A Quick Rundown

MERV, which stands for Minimum Efficiency Reporting Values, indicates a filter’s capacity to capture particles sized from 0.3 to 10 microns, essentially reflecting its efficacy in purifying the air.

The MERV ratings range from 1 to 16, where a rating of 1 signifies lower particle-trapping efficiency, and 16 represents the highest performance. Hence, a higher MERV rating corresponds to a more effective filter.

This standardized rating system originates from testing conducted by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). It is recognized as the industry standard for filter ratings both nationally and internationally.

While each air filter is assigned a specific MERV value independently, these ratings are valuable for comparison when specific requirements need to be met. For instance, when selecting a filter tailored for allergies (discussed further in the Best MERV Rating For Allergies section) or one suitable for homes with pets.

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It’s crucial to note that MERV ratings exclusively pertain to particulate filters and do not address a filter’s capability to eliminate volatile organic compounds (VOCs) or ozone.

Nevertheless, air filters with MERV ratings remain widely utilized in residences, businesses, and homes throughout the United States and internationally.

Read: Why does my Furnace Filter get dirty so quickly?

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How to Read MERV Ratings

As stated in the section above, MERV ratings go from 1 to 16. Higher ratings mean that filters are more efficient and effective at cleaning air, while lower ratings mean that they can only trap larger particulates.

In the chart below, you can see a basic rundown of the different MERV ratings and what they mean:

MERV RatingAverage Particle Size Efficiency (Microns)
1 – 43.0 – 10.0; less than 20%
6 – 73.0 – 10.0; 49.9%
8 – 93.0 – 10.0; 84.8%
10 – 11– 3.0; 50%  – 64.9%3.0 – 10.0; 85% or greater
12 – 13– 3.0; 80%  – 89.9%3.0 – 10.0; 90% or greater
14 – 150.3 – 1.0; 75%  – 84%1.0 – 3.0; 90% or greater
160.3 – 1.0; 75% or greater
MERV rating chart

So for a filter that has a MERV rating of 4 or below, it can only trap particles that are between 3.0 and 10.0 microns. And of those, it traps less than 20%.

Contrastingly, a filter boasting a MERV rating of 14 or above demonstrates the ability to capture particles as minute as 0.3 microns. Specifically, it effectively traps at least 75% of these diminutive particles.

The purpose of the rating system is to project the filter’s performance in a worst-case scenario. While filters commonly outperform their ratings, the system guarantees that filters never fall below the expected level of performance.

What MERV Rating Should I Use?

Currently, the ASHRAE recommends using a filter with a MERV rating of at least 13, but preferably 14 or higher.

However, they do note that owners should also take the capabilities of their current HVAC systems into consideration when choosing a filter.

Residential houses typically use filters with MERV ratings from 1 – 12. 

For context, these are the type of places that may use filters with various MERV ratings:

  • 1 – 8: Filters with a MERV rating of 1-4 are usually found in residential A/C units, while filters with a MERV rating of 5 – 8 can be found in residential houses, commercial buildings, and industrial workspaces.
  • 9 – 12: Filters with a MERV rating 9 – 12 are found in higher quality residential, commercial, and industrial buildings. Filters with this rating may also be used in hospital laboratories or medical areas that do not involve surgery.

The highest ratings, 13 – 16, are more commonly found in hospitals and other places that perform general surgery.

Dirty furnace filter

Consider your personal requirements and those of your household members. If you or others in your home have allergies, asthma, respiratory issues, or compromised immune systems, opt for filters with higher MERV ratings.

In situations where health conditions are a concern, a MERV rating of at least 10 is advisable, adjusting based on the severity of the mentioned conditions. Conversely, if you’re in good health and reside in an area with low air pollution, filters with lower MERV ratings may suffice for your needs.

For households without specific health concerns, filters with lower MERV ratings could be suitable.

What MERV Rating Does Trane Recommend?

This is a bit of a trick question, since Trane doesn’t technically recommend MERV ratings at all. Instead, they use a comparable rating system called the Clean Air Delivery Rate (CADR), developed by the Association of Home Appliance Manufacturers (AHAM).

According to Trane’s website, this system “measures the effectiveness of air cleaning appliances. The higher the clean air delivery rate, the more effective the unit is at cleaning the room or home of airborne particles and allergens.”

Trane clean air delivery rate chart

This outlines another primary difference: MERV ratings apply specifically to filters, while the CADR ratings apply to appliances that contain filters or have filter capabilities. More specifically, the CADR rating system was developed in response to the rise of air purifiers.

Read: Does My HVAC System Purify The Air?

Despite these differences, CADR is recognized by the Federal Trade Commission (FTC) and the Environmental Protection Agency (EPA) as a “fair and objective measure” of technology air filtration.

Similar to MERV, higher ratings are better; the higher the rating, the more effective the appliance is at removing particles and cleaning the air.

CADR ratings are broken down into three categories: tobacco smoke (10 – 450), pollen (25 – 450), and dust (10 – 400). Typically, appliances have ratings listed on them for each category.

Based on particle sizes, this is how CADR ratings and MERV ratings compare:

CADR CategoryCADR Rating (Particle Size)MERV RatingParticle Size
Tobacco Smoke10 – 450 (0.06 – 1.0 microns)14 – 160.3 – 1.0 microns
Pollen25 – 450 (5 – 11 microns)1 – 131.0 – 10.0 microns
Dust10 – 400 (0.5 – 3 microns)14 – 150.3 – 3.0 microns

These ratings are based on cubic feet per minute of clean air delivered for a typical 3-ton heating and/or cooling system.

Which MERV Rating and CADR Rating Does Trane Recommend Overall?

Based on two out of the three categories evaluated (smoke and dust), filters with higher MERV ratings are preferred. This is further evidenced by their brand name air quality systems, the Trane CleanEffects™ Air Cleaner and the QuikBox™ Media Cabinet.

Read: Why is Indoor Air Quality Important?

The former asserts its capability to eliminate up to 99.89% of airborne particles as tiny as 0.1 micron, surpassing even the most exceptional MERV rating, which typically addresses particles starting from 0.3 microns.

Nevertheless, the QuikBox™ Media Cabinet provides MERV ratings for its furnace and air handler replacement filters, featuring ten distinct models, all equipped with filters boasting MERV ratings of 11. Additionally, Trane’s Trane Comfort Performance Filter specifies a MERV 9 performance rating.

Considering their own product range, Trane seems to endorse MERV scores of 9 or higher. However, for more rigorous air purification, higher ratings seem to be their preference.

What MERV Rating Can My Furnace Handle?

When considering filters for your furnace, there are two factors to consider:

  • Furnace-filter fit
  • Filtering capability

Concerning fit, it’s crucial for your air filter to snugly fit into your furnace, without any gaps or open spots. Finding filters with the desired filtering capacity might be challenging depending on your furnace size.

Changing a furnace filter

Before selecting an air filter, measure your furnace. While filter packaging typically displays dimensions, furnaces usually don’t. Rather than guessing, measure in advance to ensure the chosen filter fits without requiring modifications.

Regarding filtering capacity, MERV ratings play a vital role. When determining the suitable rating for your furnace, strike a balance between your preferences and practicality.

For instance, while desiring the highest MERV score might seem ideal, ratings of 14 or higher are typically necessary only for institutions like hospitals. Aim for filters within the 8 – 13 range, aligning with the ratings most modern furnaces can accommodate.

Filters in this range usually integrate seamlessly with furnaces and other equipment, avoiding undue stress on the system. However, regular air filter replacements are still necessary.

In contrast, filters with higher ratings may require system modifications, since your furnace is probably going to struggle to pull air through a filter that’s rated 14 or higher. Depending on the age of your furnace, it may be necessary for you to consult a professional regarding its capabilities.

Read: How to choose a furnace filter

Best MERV Rating for Furnace Filters

Furnaces are essential to maintaining air quality within our home. They have to contend with pet dander, garage emissions, dust mites, pollen, and so much more.

But don’t fall into the trap of extremes that many homeowners fall victim to:

  • Low MERV Ratings – Poor quality filters allow too many particles into the furnace, filling it with debris, hindering its ability to function, and potentially damaging it.
  • High MERV Ratings – On the flip side, a filter that’s too powerful does the same thing: it hinders air flow, reduces a furnace’s performance, and may damage your equipment.

With this in mind, it’s best to avoid the two extreme ends of the MERV rating scale. Once again, 8 – 13 are the best MERV ratings for furnace filters.

This range suits most modern furnaces, including some older models. Filters with these ratings effectively eliminate a broad spectrum of particulates and allergens without causing disruption or overloading your system.

The specific rating choice may hinge on your furnace’s capacity or your home’s particular needs. For households with pets, urban dwellers, or those with severe allergies, filters in the 10 – 13 range are likely the most suitable.

Once you’ve settled on the desired MERV rating, you can also contemplate the filter type. Generally, filters fall into two categories: washable and disposable.

Financial considerations also come into play. Higher MERV scores correlate with increased costs. While some families may find it easy to afford and maintain a higher-rated filter, others may not.

Although every home is unique, the general guideline for furnaces is to change the filter every 90 days, translating to four changes annually, once every three months. Striking the right balance between affordability, necessity, and your furnace’s capacity is essential, though challenging—it’s a worthwhile endeavor.

Read: What affects indoor air quality?

Best MERV Rating for Allergies

The best MERV ratings for allergies depends on what you’re allergic to. Each type of allergen has a different size, such as 11 microns, 5 microns, etc.

Generally, the larger your allergen is, the more options you have for filters. But smaller allergens will require filters with higher MERV ratings. Depending on the allergen you’re looking to remove and its size, there may be a range of MERV ratings that meet your needs.

Below is a chart of the different MERV ratings, the particle sizes they remove, and examples of corresponding allergens and other particles.

MERV RatingParticle SizeExamples of Allergens & Particles
1 – 410.0 microns or greaterPollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, and carpet fibers
5 – 83.0 – 10.0 micronsMold spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix
9 – 121.0 – 3.0 micronsLegionella, humidifier dust, lead dust, milled flour, auto emission particulates, nebulizer droplets
13 – 160.3 – 1.0 micronsBacteria, droplet nuclei (sneeze), cooking oil, most smoke and insecticide dust, most face powder, most paint pigments

If you have allergies but are unsure what triggers them, filters with MERV ratings of at least 9 (but preferably higher) are your best bet for reducing symptoms. A quick and easy way to find high-rated filters is to check for pleating. Pleated filters usually have a higher MERV rating, while non-pleated filters have lower ratings.

You can also look for filters that specifically say ‘allergy’ or an equivalent on the packaging. Though filters with higher MERV ratings will remove common allergens, those specifically geared for people with allergies may have additional features that specifically target these issues.

Types Of Furnace Filters And Their MERV Ratings

There are several different types of air filters commercially available. Each one has different benefits and drawbacks, in addition to having a different MERV rating.

Generally, the MERV rating for the different types are as follows:

  • Disposable Fiberglass – Made of spun fiberglass, this is the cheapest type of furnace filter. It’s very inexpensive, but doesn’t really clean the air beyond removing the largest particulates. MERV ratings are usually 2 – 3.
  • Disposable Pleated – This popular option is often made of polyester or cotton paper. It does remove larger particulates, but also stands a higher chance of clogging your system more quickly. MERV ratings are usually 5 – 6.
  • High-Efficiency Pleated – This option is best for those with allergies, as it’s made of thick synthetic cotton, and filters out most particulates, both small and large. MERV ratings range from 10 – 16.
  • Disposable Electrostatic – This self-charging fiber filter does a great job of trapping large particulates and can even be ordered in custom sizes (albeit this is more expensive). MERV ratings are usually 10 – 11.
  • Reusable Electrostatic – Instead of replacing this filter, it’s machine washable and can last up to eight years. Despite how eco-friendly it is, this version is slightly less effective than its disposable counterpart. MERV ratings are usually 8 – 9.
  • Polyester – For those interested in fiberglass, this is a higher performance option. It’s denser, removes more particulates, and comes in flat and pleated versions. MERV ratings range from 6 – 8.

The last type of air filter doesn’t quite apply to this list since it doesn’t have a traditional MERV rating.

You’ve no doubt heard of high-efficiency particular air filters, also known as HEPA air filters. They block and remove up to 99.7% of airborne particles that are 0.3 microns or larger. Some even claim to remove particles that are smaller than 0.3 microns, which is what removes it from the MERV ratings we’ve been discussing so far.

Hepa filter cut-away diagram
Hepa Filter, courtesy of iso-air.com

Additionally, these filters are very thick and not suitable for residential furnaces. They’re also not readily available in standard sizes, which also poses a problem. Instead, these filters are used almost exclusively by hospitals and other organizations which require a very high standard of air quality. Thus, if they had a MERV rating, it would be in the unofficial range of 16 – 20.

Comparable Rating Systems

Despite MERV ratings being the recognized industry standard, they aren’t the only filter rating systems currently in use. There are three others that commonly appear: ISO ratings, FPR ratings, and MPR ratings.

Owners can also take the International Organization for Standardization’s (ISO) ratings into consideration. These filter ratings are comparable to MERV ratings, as outlined below.

MERV Rating (Standard 52.2)ISO Rating (Standard 16890)
1 – 6ISO Coarse
7 – 8ISO Coarse >95%
9 – 10ePM10
11 – 12ePM2.5
13 – 16ePM1

An ISO rating of ePM10 means that the filter can remove particulates ranging from 0.3 to 10 microns. Filters that are rated ePM2.5 can remove particulates ranging from 0.3 to 2.5 microns, and an ePM1 rating means that the filter can remove particles as small as 0.3 to 1.0 microns.

The EPA, World Health Organization (WHO), and European Union all use the same definitions regarding ISO ratings and particulate matter size ranges. Therefore, it’s useful to understand ISO ratings and their MERV equivalent. This way, you’ll understand a filter’s rating no matter which system it uses.

Besides these ISO ratings, there are two other commonly used rating systems: Filter Performance Rating (FPR) and the micro-particle performance rating (MPR).

Both of these were created by commercial businesses for marketing purposes. FPR was developed by the Home Depot, and MPR was created by 3M. Neither is recognized internationally.

The FRP rating uses a reduced scale of 4 through 10. It rates filters in broader terms: the ability to capture large particles, ability to capture small particles, and weight change over the filter’s lifetime. Each rating is also coordinating with a color-coding system for visual aid and ease of reference.

The MPR rating is based on particle size, from 0.3 to 1.0 microns. It exclusively rates filters on their ability to remove particles smaller than 1.0 micron and does not take larger microns into consideration. 

This can be frustrating, since many allergens are larger than 1.0. For example, dust particles can be as large as 8 microns and pollen can easily clear 7 microns. Therefore, it is an extremely limited rating system.

Here’s an example of how both compare to four different MERV ratings:

MERVFPRMPR
6N/A300
84600
1171,000 – 1,200
13101,500 – 1,900

Though the FPR and MPR rating systems aren’t as widely recognized or used as MERV, they are still effective and maintain strict quality standards.

Therefore, if a customer is looking for a MERV-rated filter but can only find a comparable FRP-rated one, the customer can still have confidence in the filter’s performance.

Related: Do I need Filters in my Return Vents?

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