These days you can find an equal amount of air pollution inside your homes as that of the outdoors. Lack of proper ventilation systems is a major reason for this as an area with little or no ventilation is more prone to trapping contaminants and pollutants found commonly at your homes than anywhere else. Clean air is a necessity. And to provide clean air for your indoors, air purifiers and utilized.

You must have come across the words like MERV or HEPA while looking for a furnace filter. People often tend to confuse between high ratings and efficiency. In this article, we are going to put a stop to your confusion and explore everything about MERV as well as HEPA filters along with the details of MERV vs. HEPA filters. Before jumping onto the main topic, let us first have a brief idea about how do air purifiers work.

How Do Air Purifier Filters Essentially Work?

HEPA vs MERV | What Air Purifier Filter Is the Best?

The filter media of air filters is comprised of several fibers arranged in a criss-cross manner, layered up in random directions. When the air along with the particles from the working environment enters the filter, the particles get intercepted by the fibers and further subjected to filtration mechanics. The filtration mechanics rely upon the airflow velocity and the size of the particle.

Few filtration mechanics with their respective definitions are as follows:

  • Interception: When a dust particle follows a gas streamline that comes in contact with the surface of a fiber.
  • Inertial impaction: When, due to the inertia of a dust particle, it collides with a filter fiber.
  • Diffusion: When the particles are governed by Brownian motion (random motion) and don’t follow gas streamlines.
  • Electrostatic attraction: When there is a presence of electrostatic charge on the filter fibers.

The bigger particles coming across the filter will in general fall onto the outside surface of the filter media. The smaller particles following the airflow streamlines tend to fall onto an intercept between the depth of the engine filter media as the filter fiber behaves as branches that trap contaminants surpassing the filter. Refer to this guide for a detailed overview on the working of air purifiers and their effectiveness.

What Is A MERV Filter Rating?

While selecting an air filter, the most important thing to look for is finer filtration. MERV is the abbreviation of Minimum Efficiency Reporting Value. MERV rating for an air filter determines the level of efficiency of the filter in terms of removing all sorts of unwanted particles and allergens like pet dander, dust, and pollen from the air having a size between 0.3 microns to 50 microns. This rating was developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) in 1987. The primary focus while developing this was to compare the filtering efficiency of a variety of air filters. It is to be noted that a MERV rating can only be assigned to an air filter that physically traps and eliminates airborne contaminants. This excludes activated carbon filters, air ionizers and ozone generating air purifiers. Usually, the MERV rating ranges from 1 to 16 with 1 being the lowest and 16 being the highest concerning air filter efficiency. A high MERV-rated filter is considered to be ideal for homes with allergy and asthma patients. We’ve carefully compiled a list of highly effective air purifiers for allergies for your reference.

The filters that have a rating between 1 to 4 MERV are said to be low-grade filters. A filter ranked between 5 to 12 MERV is considered a medium-grade filter. These filters are able to remove dust, hair, dust mites, mold, and pollen. However, a high-efficiency filter is rated between 13 to 16 MERV. Filters with a 13 to 16 MERV rating remove about 75% or more airborne particles. A filter having an exact 16 MERV has the capability to capture >95% of particles ranging between 0.3 to 1.0 microns in size. Nevertheless, one should remember that the MERV values are not standard and vary with brands.

The table given below depicts the MERV rating scale, capturing efficiency, filter types, and the types of particles that the filter can capture.

RATINGS      0.3–1 MICRONS        1–3 MICRONS      3–10 MICRONS FILTER TYPE CONTROLLED PARTICLES
MERV 1 <20% Pre-filter / Aluminum Mesh Dust, dust mites, pet dander, pollen
MERV 2 <20%
MERV 3 <20%
MERV 4 <20%
MERV 5 20-34% Low-Quality MERV Filter Mold, spores, cooking dust, hair spray
MERV 6 35-49%
MERV 7 50-69%
MERV 8 <20% <70%
MERV 9 <35% <35% Standard MERV Filter lead dust, smaller mold, smaller pollen
MERV 10 50-64% <75%
MERV 11 <20% 65-79% <80%
MERV 12 <35% 80% <85%
MERV 13 <50% <90% <90% Superior MERV Filter Bacteria, viruses, fine dust
MERV 14 75-84% <90% <90%
MERV 15 85-94% <90% <90%
MERV 16 <95% <95% <95%

What Is A HEPA Filter Rating?

HEPA stands for High-efficiency Particulate Air. The only filter to have tested and certified for meeting a specific efficiency within a particular particle size is a HEPA filter. It is mandatory for all the HEPA filters to have a minimum efficiency of 99.97% at 0.3 microns. These filters do not have MERV ratings because they surpass the ASHRAE test protocol 52.2 utilized in deciding the MERV ratings. HEPA filters need a fan to filter the air which means an HVAC system has to be compatible with a HEPA filter to work efficiently or else it will have to try to generate more power to move air tough the filter. This will subsequently increase your electric bills alongside the strain on your filter system. HEPA filters are capable of removing at least 50% more respirable-sized airborne particles than any of the ASHRAE air filters available in the market.

HEPA filters are mostly utilized in hospitals to help prevent the spreading of infections and maintain a microbe-free environment. While purifying, a force of airflow from the filter pulls the particles towards themselves. The filter’s fiberglass threads (filter media) traps these particles and prevent them from proceeding further. While a few of the particles get caught by the curved contours of the fibers, most of them adhere to the fibers when they hit. The left-out particles get trapped while colliding with other molecules in the filter. This, in turn, produces and exhausts purified air into the atmosphere and the cleaning cycle repeats itself.

There is a slight downside to the HEPA filters. While it should trap impurities for clean air circulation, not all ventilation frameworks are well suited with a HEPA filter. The filter tends to create a stronger resistance to the airflow due to its high fiber density. This allows less air to pass through the filter. This is the reason it requires additional fan power to push air through the filter for efficient airflow circulation.

RATINGS 0.3 – 1 MICRONS 1 – 3 MICRONS 3 – 10 MICRONS FILTER TYPE CONTROLLED PARTICLES
MERV 17 99.97% <99% <99% HEPA / ULPA Filter Small bacteria and viruses, fumes
MERV 18 99.997% <99% <99%
MERV 19 99.9997% <99% <99%
MERV 20 99.99997% <99% <99%

Recommended: What is A CADR Rating? Is it A Reliable Qualitative Metric?

Beware Of HEPA Type / HEPA like Filters

HEPA vs MERV | What Air Purifier Filter Is the Best?

True HEPA filter isn’t equivalent to a HEPA-type filter. Despite the fact that both are mechanical filters, there lies a hell and heaven difference in their pricing, density, and filtration efficiency. A True HEPA filter has the power to capture 99.97% of airborne particles as small as 0.3 microns. This may include dust mites, pet dander, mold, pollen, bacteria, and viruses as we have discussed in the above paragraphs. A true HEPA filter is rated between 17-20 MERV. Whereas in case of HEPA-type filters, it can be considered as an inferior version to a True HEPA filter. It is gaining attention just because of its low cost. It is made up of thin fiber glass but with low density as compared to a True HEPA due to which finer particles surpass the filter. A HEPA-type filter is commonly found in the lower-end air purifier.

If you come across a filter mentioned as HEPA- like, type or style, run away. Do not even consider buying it just because it’s cheaper. These filters will fail to satisfy or meet HEPA standards and you’ll be wasting your money anyway. Even though they have a similar design and build, they have a lower efficiency and are just like the regular vacuums or regular air purifiers. Referring to a filter as HEPA Type filter is essentially meaningless, as it does not conform to any standard. It is certainly just a marketing term. It is either HEPA or NOT HEPA. There is no in between!

Verdict | Are HEPA Grade Filters Better Than MERV Rated Filters?

HEPA filters are hands down the best air filter as they have an effective top-tier MERV 17 to 20 rating that exceeds even a MERV 16 filter. If we consider a HEPA filter, it is able to capture a minimum of 99.97% contaminants from the air of size 0.3 microns. Whereas in the case of MERV 16 filters, they capture about >95% of particles of size 0.3 to 1.0 microns. HEPA filters are utilized in nursery homes, educational institutions, and healthcare applications like anterooms, surgery rooms, isolation wards due to their high particle removal efficiency. However, if you do not suffer from any allergy or respiratory disease, a general MERV 5-8 rated filter shall do for your house. But for most households, a MERV filter with a 9 and above rating is considered the best. It proves to be effective even at the lower tier against finer particles like mold, pollen, spore, and VOCs released from cleaning products. In addition, superior MERV-rated filters (13-16) are employed in commercial set-ups having 75% or greater filtration capacity.

Both HEPA and MERV are intended to enhance indoor air quality and ventilation. Nevertheless, not all air filters are alike. While selecting an air filter, you should give it a thought to your requirements and evaluate the air quality in your home. Checking up with your furnace system before installing a filter is also a significant point. An HVAC personnel might help you decide what kind of filter is best for your system.

Eventually, all it comes down to a well-balanced ventilation system. Having a MERV filter in your HVAC system facilitates the circulation of clean air as the air in your home is constantly being recirculated. In case your HVAC system doesn’t support HEPA or MERV filter upgrade, a HEPA purifier for every room could help. You just need to turn it on with at least 2 air changes per hour.

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