HEPA vs MERV: The Furnace Filter Battle

Having clean indoor air can help a person breathe better and reduce allergy symptoms. Whether you are looking for a furnace filter, the word MERV or HEPA will pop out. Most people tend to lean towards a higher number without knowing why. In this post, we will end the confusion and explore everything about MERV. Starting with what are the ratings for and how should I use them? What types of filter has the best ratings for home use? Lastly, should I get a HEPA or MERV filter for my furnace? Learn the difference between MERV and HEPA filters to help you decide which to go for.


What Is A MERV Filter Rating?

Acronym or Minimum Efficiency Reporting Value. Developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) in 1987, MERV is a system used to evaluate an air filter efficiency in capturing particles between 0.3 microns to 50 microns in size. With a MERV rating scale ranging from 1 to 16, the assigned value helps compare the efficiency of different filters. The higher the MERV number, the better the filter efficiency in trapping fine particulate matters. A low-ranking filter is rated between 1 to 4 MERV, and a medium grade filter has 5 to 12 MERV ratings. Filter in this range can remove dust, hair, dust mites, mold, and pollen. A high-efficiency filter is rated between 13 to 16 MERV. The most superior MERV filter removes 75% or greater airborne particles. A MERV 16 filter will capture >95% of particles ranging between 0.3 to 1.0 microns in size. The filter in this group can target biological growth, chemical fumes, volatile organic compounds, and smoke. Keep in mind that MERV values may vary from one brand to the other.

The table chart below shows the MERV rating scale and average arrestance, filter type, and particle sizes a filter can capture.

Ratings0.3 – 1 microns1 – 3 microns3 – 10 micronsFilter TypeControlled Particles
MERV 1<20%Pre-filter/ Aluminum MeshDust, dust mites, pet dander, pollen
MERV 2<20%
MERV 3<20%
MERV 4<20%
MERV 520-34%Low Quality MERV FilterMold, spores, cooking dust, hair spray
MERV 635-49%
MERV 750-69%
MERV 8<20%<70%
MERV 9<35%<35%Standard MERV Filterlead dust, smaller mold, smaller pollen
MERV 1050-64%<75%
MERV 11<20%65-79%<80%
MERV 12<35%80%<85%
MERV 13<50%<90%<90%Superior MERV FilterBacteria, viruses, fine dust
MERV 1475-84%<90%<90%
MERV 1585-94%<90%<90%
MERV 16<95%<95%<95%

What Is A HEPA Filter Rating?

Acronym for High-efficiency Particulate Air. A HEPA filter is ranked between 17-20 MERV, the highest group in MERV ratings. All HEPA filters are tested and certified to be at least 99.97% efficient in removing particles as small as 0.3 microns. HEPA filters are used in all hospitals to stop the spread of infections and keep them in the bay. This includes bacteria and viruses that are highly contagious in indoor airspace.

Filter media is made up of dense fiberglass threads compressed in unsystematic directions. The purification begins when airflow forces the particles towards the filter. The filter’s fiberglass would then intercept the particles from proceeding. Most particles will adhere to the fibers when they hit, while some get caught by the curved contours of the fibers. The remaining airborne particles will be trapped when they collide with other molecules in the filter. This leaves only purified air exhausted into the air, and the cleaning cycle will repeat itself.

There is a slight drawback to the HEPA filter. While it is supposed to trap impurities for clean air circulation, not all ventilation system is compatible with a HEPA filter. The high fiber density of a HEPA will create a stronger resistance to the airflow; less air would bypass the filter. Without additional fan power to push air through the filter, the airflow circulation would be inefficient and stagnant. In the long run, the wrong filter setup can increase your electricity bills, put extra strain on the system, and eventually damage the HVAC system due to the increased pressure. True HEPA filters are not washable as doing so will damage the density of the fibers. It has to be disposed of and replaced when it is worn out.

Ratings0.3 – 1 microns1 – 3 microns3 – 10 micronsFilter TypeControlled Particles
MERV 1799.97%<99%<99%HEPA/ ULPA FilterSmall bacteria and viruses, fumes
MERV 1899.997%<99%<99%
MERV 1999.9997%<99%<99%
MERV 2099.99997%<99%<99%

MERV or HEPA filters: Which Is Better?

The HEPA filter is the best as it is essentially a top-tier MERV 17 to 20 rating that surpassed even a MERV 16 filter. A HEPA filter can capture a minimum of 99.97% impurities in the air as small as 0.3 microns VS MERV 16 filter that captures >95% of particles from 0.3 to 1.0 microns. Given the high particle removal efficiency, HEPA filters are regularly used in nursery homes, educational institutions, and healthcare applications like anterooms, surgery rooms, isolation wards. If you don’t have any allergy or respiratory illnesses, a basic MERV 5 to 8 rating filter will be sufficient in removing dust, dust mites, and pet dander after a few cycles. Suitable for a household that does not have any major air quality concerns. You should go with filters with MERV 9 rating and above for most homes. Even at the lowest tier, it is effective against finer particles like mold, pollen, spore, and VOCs released from cleaning products. Moving on, filter with superior MERV ratings 13 to 16 are commonly used in commercial structures with a superior 75% or greater filtration to capture microscopic particles and prevent the spread of viruses. Ideal for a person who has asthma, chronic diseases, or a weak immune system.

Breathing to clean air is vital to our health and can prevent diseases from spreading. MERV and HEPA filters are designed to improve ventilation and indoor air quality, but not all filters are created equal. To choose the right air filter, understand your needs, and evaluate the air quality in your home. You will also need to find out more information about your furnace system before attempting to install a MERV or HEPA filter. Speak to an HVAC professional to determine what kind of filter is best for your system.

Ultimately, a well-balanced ventilation system is the way to go. As the air in your home will constantly be recirculated, having a MERV-rated filter in your HVAC system will ensure clean air can be achieved. If your HVAC system does not support MERV or HEPA filter upgrade, get a H13 HEPA air purifier for every room and turn it on with at least 2 air changes per hour.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.
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