Your Ultimate Guide To MERV Ratings

If you are shopping for an air purifier filter, you've probably heard about MERV ratings. So, what is MERV rating on filters, and why is it important? MERV is short for Minimum Efficiency Reporting Values. MERV rating is used to determine a HEPA filter’s ability to capture particles in the air between 0.3 and 10 microns. HEPA — High-Efficiency Particulate Absorbing — is a type of filter that can trap 99.97% of airborne particles that are 0.3 microns. In simple terms, a HEPA filter can trap particles that other kinds of air filters may not. 

MERV ratings can help consumers compare the performance of various air purifier filters on the market. Air purifier replacement filters with high MERV ratings are ideal for filtering out even the smallest of airborne particles from indoor spaces.

If you’re  wondering, "what  does MERV rating mean?" we can explain in more detail. Keep reading  to learn more about common indoor air pollutants, why you should care about the quality of indoor air, and how to leverage MERV rating when choosing a HEPA filter for your air purifier.

Why you should care about indoor air quality

Indoor air quality is  more than just eliminating unpleasant odors or reducing the number of allergens in the air you breathe, it is about preserving your health. According to the Environmental Protection Agency, we spend an average of  90 percent of our time indoors. The concentrations of some pollutants are 2-5 times higher indoors than they are in a typical outdoor environment. This  boosts your risk for developing certain illnesses and diseases. Young children and older adults are the most susceptible.

The World Health Organization tracks health-related issues affected by poor-quality indoor and outdoor air. According to WHO’s most recent data, nearly 4 million people die prematurely each year from illnesses attributed to household air pollution. Of those deaths:

  • 27% are from pneumonia. The risk of childhood pneumonia is nearly doubled and is responsible for roughly 45% of deaths in children under 5.
  • 18% are from a stroke. Exposure to household air pollution from cooking with solid fuels and kerosene is linked to deaths from stroke.
  • 27% are from ischemic heart disease. This accounts for more than a million premature deaths each year.
  • 20% are from chronic obstructive pulmonary disease (COPD). Adults in low- and middle-income countries are the most susceptible, with women more likely to develop COPD than men.
  • 8 percent are from lung cancer. Carcinogens in household air are the main culprit. These include wood, charcoal, and kerosene.

Why is indoor air so unhealthy? Part of the problem is our push toward energy efficiency. We have made homes so air-tight that the indoor air becomes stale and polluted without proper ventilation. Any airborne particle easily travels throughout your home, reducing the air quality. Relying on an air purifier with a HEPA filter is one of the best ways to reduce indoor air pollution. Some of the best HEPA air purifiers on the market use filters with MERV ratings for their effectiveness at combating indoor air pollutants.

Common sources of indoor air pollution

Energy efficiency is one of the biggest culprits for trapping unhealthy airborne particles inside homes. However, it is not the source of indoor air pollution. When it comes to the not-so-good  things floating in the air we breathe at home, there are several major sources that can be found in most households.

1. Mold and mycotoxins

A biological source of air pollution, mold and other mycotoxins are found in about 70 percent of all indoor spaces. An overabundance of moisture is a contributing factor. Mold can trigger allergy and asthma symptoms in people who are sensitive to it. Even with people who are not sensitive to mold, prolonged exposure to it can irritate the eyes, nose, throat, and skin.

2. Pet dander and dust mites

People love their pets. That’s why 67 percent of U.S. homes include at least one furry friend. Pet dander, dead skin cells your pet sheds, is a major allergen. When there’s a lot of pet dander in your home, you attract another common source of indoor air pollution: dust mites. Dander is dust mites' primary food source. While you might think it's good that dust mites eat the dander that pollutes indoor air, there is a downside. Dust mites’ dead bodies and the waste they produced contribute to unhealthy indoor air.

3. Gas-burning appliances

Appliances that use natural gas or propane, including stoves and furnaces, can release harmful toxins like carbon monoxide into the air. Other culprits include wood-burning fireplaces and kerosene space heaters.

4. Cleaning supplies

The chemicals found in most modern cleaning supplies release harmful chemicals into the air every time you use them to sanitize your home. Some of the most popular household cleaners contain toxic ingredients such as phthalates, triclosan, PERC, and ammonia. The fumes from these cleaners tend to linger in the air, thus increasing your risk of inhaling them.

5. Tobacco smoke

Cigarettes. Cigars. Pipes. The method of delivery doesn’t matter. If you or a family member are smoking inside your home, you or they are releasing toxic chemicals that can impact indoor air quality.

6. Home improvement products

Paints, finishes, and raw building materials are necessary for making home improvements, but they’re also major contributors to indoor air pollution. These products contain volatile organic compounds (VOCs) that release harmful gases into the air.

There are other factors affecting indoor air quality, such as air exchange rate, outdoor climate, and weather conditions. The air exchange rate refers to the air that’s  exchanged indoors and outdoors, and building design plays a huge role in this. Also, whether windows and doors are open or closed and if the heat or air conditioning is turned on will depend on the outdoor climate and weather conditions.

Improving your indoor air quality

If your indoor air quality is poor, the good news is, there are mitigation strategies to help enhance the quality of the air you are breathing. Here are the three methods the EPA recommends for the most effective results.

1. Locate the source

Source control is all about removing the cause of poor indoor air quality. If you can locate and eliminate the cause, it’s  the best possible outcome for improving air quality. Let’s say the main pollutant plaguing your indoor air quality is tobacco smoke. Someone in the household prefers to smoke cigarettes, cigars, or a pipe indoors. Requiring all smokers to indulge their habit outdoors is one way to apply source control.

However, it’s not always possible to completely remove the source. For instance, if your air is mainly polluted by pet dander, getting rid of your furry friends is not a solution most pet owners would embrace.

2. Ventilate

Proper ventilation can help improve indoor air quality, especially if you have a lot of VOCs inside. As mentioned earlier, a common source of VOCs is household cleaning products. It is nearly impossible to completely rid our indoor spaces of hazardous air pollutants. The good news is, HVAC systems that bring in fresh air from outside can help. Airflow must be consistent for it to work though. So, during milder weather, when neither the heat nor the air conditioning is running, indoor air quality is diminished.

When the weather is mild, opening doors and windows can help improve airflow in your home and other indoor spaces. However, make  sure to check the pollen count and air quality index levels before letting the outside air into your home. Individuals with allergies or asthma can experience symptoms if pollen counts are high or if outdoor air quality is lacking.

3. Purify

Using an air cleaner to purify your indoor air is another excellent solution. As the name implies, these devices cleanse and purify the air, removing particles and gases that can make us sick. Air purifiers with a HEPA filter are the most efficient at recycling stale, dirty  indoor air and making it fresh and healthy. You can purchase a whole-house air purifier or choose ones that target smaller indoor spaces. Some air purifiers are rated only for common allergens and viruses, while others handle almost all airborne particles. All air cleaners require periodic cleaning and maintenance, which includes air filter replacement.

What MERV rating is best?

Now that you know what’s potentially present in your indoor air and why you should care, let’s talk about what MERV rating is best. MERV ratings range between 1 and 20. The higher the MERV rating on a filter, the fewer airborne particles and contaminants can pass through it. 

When the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) designed the MERV rating scale, they did so with the worst-possible performance for removing particles with 0.3 to 10 microns in mind. These are some of the smallest airborne particles and, therefore, the toughest to filter out.

Here are some general guidelines to keep in mind when deciding what MERV rating is best for your needs:


MERV Ratings 1-4

These are commonly used for residential furnaces, window air conditioning units, and pre-filtered commercial buildings. At this rating, the filter can control carpet fibers, dust mites, pollen, and textile fibers. It filters down particles 10 microns in size.

MERV Ratings 5-8

These are used in commercial, residential, and industrial buildings. They are efficient at controlling carpet fibers, concrete dust, dust mites, household dust and lint, mold spores, and pollen. It filters down particles 3 to 10 microns in size.

MERV Ratings 9-12

These filters are reserved for commercial and residential buildings that need above-average air quality. Hospital labs also use them. They filter down particles 1 to 3 microns in size and control carpet fibers, coal dust, concrete dust, dust mites, humidifier and nebulizer dust, lead dust, and legionella and mold spores.

MERV Ratings 13-16

Commercial or residential buildings that need top-notch air filtration (hospitals, in-patient care facilities, nursing homes) rely on filters with this rating. It controls all the same contaminants for the MERV 1-12 ratings, plus bacteria, copier ink fumes, cosmetic dust, insecticide dust, pet dander, sneeze particles, tobacco smoke, and vehicle fumes. It filters down particles 0.3 to 1 micron in size.

MERV Ratings 17-20

These filters are usually reserved for pharmaceutical manufacturers, orthopedic surgery facilities, and for removing radioactive and carcinogenic materials.


What is the highest MERV rating? 

MERV Ratings of 17-20 are  the best of the best — this is why these filters are generally reserved for pharmaceutical manufacturers, orthopedic surgery facilities, and for removing radioactive and carcinogenic materials. In addition to all the particulates for MERV Ratings 1-16, it handles carbon dust, combustion smoke, microscopic allergens, radon progeny, and virus carriers.

What MERV rating is best for home use? According to ASHRAE, a MERV 13 rated filter is sufficient for controlling the most common indoor pollutants in residential buildings.

What MERV rating is a HEPA filter?

What MERV rating is HEPA? HEPA filters are not MERV rated per se. However, in a side-by-side comparison, HEPA filters have an even higher performance than MERV 16, which only captures around 95% of airborne particles between 0.3 and 10 microns. A top-quality HEPA filter traps 99.97% of airborne particles with a size of 0.3 microns. If HEPA filters  were given a MERV rating, it would be between 17 to 20.

What’s  the difference between a HEPA filter and MERV ratings?

While HEPA filters are more efficient at eliminating airborne pollutants indoors, they cause too much air resistance to be used in most HVAC systems. However, they are suitable for room-size air purifiers. Allergy and asthma sufferers may wish to opt for air filtration systems that use a HEPA filter. They remove the microscopic particles most likely to be inhaled deep into the lungs, where they can trigger severe symptoms.

Some people do not like HEPA filters because they are pricier than other air purifier replacement filters. Others may dislike the “white noise” produced from pushing the air through the HEPA filter. If either of these things is concerning for you, opting for a filter with a higher MERV rating is an alternative solution.

MERV and airflow rating

Does a higher MERV rating restrict airflow? That’s  a question many people ask when searching for the best air purifier filter. If you’re wondering, "Does MERV rating affect airflow?" The short answer to that question is yes. MERV rating affects the efficiency of the air filter indirectly. As a rule, an air purifier filter with a higher MERV rating will have less airflow. This is not necessarily something to be concerned about, as it is only an issue under certain circumstances.

Air purifiers with stronger motors can accommodate the airflow issues. Air purifiers with PSC motors maintain less airflow while using the same amount of energy as other air purifiers. Meanwhile, ECM motors maintain the same airflow but use more energy. Choosing an air purifier with an ECM motor is your best bet if reduced airflow rating is a concern.

Most modern HVAC systems and air purifiers are designed to work with higher MERV filters. The biggest risk when using them is if you fail to change them out periodically.

Replacing your filters

Whether you're using a HEPA filter or a MERV-rated filter, it will require routine maintenance to work efficiently. Replacing the filter is one of the most important things you can do to keep your air purification system working properly.

We recommend changing out your HEPA filters every 6 to 12 months, while carbon pre-filters should be switched every 3 to 6 months. These are general guidelines. If you have pets or smokers in your home, you may need to replace filters more frequently. 

One of the nicest features of most modern air purifiers is they will indicate when it’s  time to replace the filter. It  takes the guesswork out of it  so you can always be sure your system is performing optimally.

If you fail to replace the filter as recommended, it’ll become too clogged and will not properly purify your indoor air as it would with a fresh filter. A worst-case scenario is that continuing to run your air purifier with a clogged filter can burn out the motor. When this happens, you will need to replace the whole purifier.

In addition to replacing the filter, it’s  a good idea to use a soft brush or damp cloth to clean the vents, as it’s  likely to have some buildup. If the piece is removable, you can wash it with soap and water for a thorough cleaning. You can also wipe down the entire exterior of the air purifier using the same technique.