There’s one number anyone who cares about indoor air quality should understand: MERV rating. This value becomes particularly important when shopping for a filter media for a home air purifier, furnace filter, or HVAC system. In this resource, I answer the questions that landed you here: What is a MERV rating and What is a good MERV rating?
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What Does a MERV Rating on a Filter Mean?
MERV stands for Minimum Efficiency Reporting Value. Developed in 1987 by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), MERV rating is a recognized filter performance value that helps homeowners, pharmaceutical manufacturers, commercial building managers, hospitals, and clean rooms compare different filters and choose the best option for their specific indoor air quality situation. Starting from 1-20, the MERV rating defines the worst-case air filtration performance of a given filter media in terms of removing particulates of a specified size range. That’s why this number matters so much.
Are Higher MERV Ratings Always Better Than Lower Ratings?
No, a higher MERV rating isn’t always better than a lower MERV rating. In most cases, a higher rating is preferable to a lower one. Because a filter with a high rating removes the tiniest airborne particles better than one with a lower rating.
However, in some situations, a lower rating would be the best option. For example: Even though indoor air quality experts say that MERV 13 is the best rating for residential use, it might overextend and possibly degrade your HVAC system.
So, if you’re not sure what the best rating for your furnace or HVAC system is, consult an experienced technician for professional advice on what rating to choose.
What Does a High MERV Rating Mean?
The higher the MERV rating, the higher the resistance to airflow. In other words, higher-rated air filters restrict airflow more compared to lower-rated ones. Put another way, a filter media with a higher rating is less energy efficient than one with a lower MERV value.
But there’s an upside: a higher-rated filter captures a greater number of airborne contaminants compared to lower-rated options. It also removes much smaller particles than does any filtration media with a lower MERV number.
If you have asthma or breathing issues, choose an air filter with a reasonably high MERV rating. Because such a filter removes larger and smaller particulates alike, purifying your indoor air in ways a lower-MERV filter can’t.
What Does a Lower MERV Rating Mean?
A filter with a lower MERV rating filters larger particles reasonably well. But when it comes to capturing smaller airborne particulate matter, a lower-rated filter really struggles to do the job.
The upside is that a lower-rated filter doesn’t restrict airflow as much as does a high-rated one. Put differently, a lower-MERV air filter is more energy efficient compared to an option with a greater MERV value.
Lower-MERV filters have widespread use in industrial applications that don’t need to filter out extremely small particulates. These filters clean the air sufficiently well while conserving energy, and this is a really desirable balance in these use cases.
A MERV Rating Chart
|MERV Rating||Application/Where Filter’s Used||Contaminants Removed||Particle Size Removed|
|MERV 1||Residential furnaces, window air con units, commercial building prefilters||Pollen, dust mites, textile fibers, carpet fibers, and sanding dust||Filters air down to 10 microns|
|MERV 5||Paint booth inlets, industrial workplaces, better commercial buildings, residential buildings, final filters, and prefilters||Pollen, dust mites, sanding dust, carpet fibers, textile fibers, mold spores, cement dust, lint dust, and sanding dust||Filters air down to 3-10 microns|
|MERV 9||Prefilters, final filters (e.g. HEPA&ULPA filters) hospital labs, better commercial buildings, superior residential buildings||Pollen, dust mites, sanding dust, carpet fibers, textile fibers, mold spores, cement dust, dust lint, lead dust, legionella, coal dust, humidifier dust, and nebulizer dust.||Filters air down to 1-3 microns|
|MERV 13||Final Filters (such as ULPA & HEPA filters), general surgery, superior commercial buildings, smoking lounges, inpatient care centers in hospitals||Pollen, dust mites, sanding dust, carpet fibers, textile fibers, mold spores, cement dust, dust lint, lead dust, legionella, coal dust, humidifier dust, nebulizer dust, bacteria, tobacco smoke, car exhaust fumes/auto fumes, copier toner dust, pet dander, face powder, and sneeze nuclei.||Filters down to 0.3–1.0 micron particle size|
|MERV 17||Final filter, clean rooms, radio active materials, carcinogenic materials, pharmaceutical manufacturing facilities, and orthopedic surgery room||Pollen, dust mites, sanding dust, carpet fibers, textile fibers, mold spores, cement dust, dust lint, lead dust, legionella, coal dust, humidifier dust, nebulizer dust, bacteria, tobacco smoke, car exhaust fumes/auto fumes, copier toner dust, pet dander, face powder, sneeze nuclei, virus carriers, sea salt, carbon dust, combustion smoke (such as wildfire), odors, radon progeny, and microscopic allergens||Filters down to less than 0.30 micron particle size|
What Are Prefilters?
Prefilters are preliminary filters and are rarely used alone. They’re normally an integral part of comprehensive multi-filter air filtration systems.
These filters serve as the first line of defense against indoor air pollution. Their main role is to capture larger debris such as pet dander, pet hair, and fibers/textile lint.
Pre-filters remove these large-sized contaminants before they reach the final filter. This prolongs the lifespan of the final filter, which cuts filtration and maintenance costs.
Below are examples of multi-filter air cleaning systems that use preliminary filters and final filters:
What Are Final Filters?
A final filter is a type of air filter used to capture super-fine particulate matter. HEPA filters and ULPA filters are good examples of final filters.
Some air purification systems, usually single-filter systems, use final filters exclusively. And that’s OK. Except you have to clean these filters more often and buy replacement filters more frequently.
What is the Best MERV Rating for a Residential Home?
According to Filter King, the best MERV rating for most residential homes lies between MERV 8 and MERV 10. These air filters remove fairly large particles (won’t remove the tiniest particles) without being too restrictive.
It’s best to use these whole-house filtration systems in combination with standalone/single-unit household air purifiers.
Is MERV 11 Too Restrictive?
It depends on what kind of HVAC system you have in your home. For some HVAC systems, MERV 11,12, or even MERV 13 may be OK. But even MERV 11 may turn out to be too energy inefficient for some HVAC systems.
Is MERV 13 Too High?
A MERV rating of 13 is pretty high. It’s normally the highest MERV rating used in residential homes. Actually, MERV 13+ air filters are hospital-grade filters and may be overkill for most homes.
Is a MERV 13 Filter Too Restrictive?
Yes, a MERV 13 air filter may be extremely restrictive for many HVAC systems. That’s why upgrading to this higher-grade filter may be counterproductive in some situations. Make sure your HVAC system would work efficiently if you upgraded it to this kind of filter.
What MERV Rating is a True HEPA Filter?
HEPA air filters aren’t normally MERV-rated. That said, True HEPA filters are considered MERV 16 to 20.
Final Thoughts on MERV Ratings
Understanding what MERV ratings are is important when looking to install a new HVAC system or furnace. Or when upgrading the existing air filtration system.
Generally, higher-rated air filters capture larger and smaller airborne contaminants better than lower-rated media. But high-MERV filters aren’t necessarily better than low-MERV ones for each and every indoor air quality situation.