What Are MERV Air Filter Ratings?

In 1968, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers released its first air filter testing standard. Nearly two decades later, ASHRAE created the Minimum Efficiency Reporting Value, aka MERV. This was an update that the society felt was necessary. The ratings, which range from 1 to 20, are used to determine the quality of any given air filter. MERV measures the filter’s efficiency by its ability to trap airborne pathogens. At Hoff Heating & AC in O’Fallon, MO, we help install air filters that meet MERV standards and recommendations.

Here are some things you should know about the MERV air filter ratings.

What Rating Should I Use?

The proper rating for your interior depends on several factors. The higher the rating, the more particles the air filter is expected to trap. If the air filter is going to be used in your home, you do not need the highest-rated air filter. However, you’ll need a filter that’s going to do the best in your HVAC system. While a filter with a high rating is wonderful, it’s not necessary for all situations. In fact, it may not be good for your system. For residential heating, cooling, and ventilation systems, there are filter recommendations. These accomplish their tasks according to the ratings, but they are not so good that they could damage the hardware.

An air filter that works too well is catching just about everything. This means that the tiny openings are almost non-existing. There has to be some air getting through the filter. If it does not, there is a good chance that the entire unit will overheat. The highest-rated filters are designed for industrial HVAC systems. Due to their size and power, those machines will not overheat. Plus, the air quality will remain solid.

The size of the particles is a major factor that determines the efficiency of the filter, too. The particle size range is 0.3 micrometers to around 10 micrometers.

So, what ratings are best for residences? Let’s discuss this now.

MERV Rating 1 – 8

An air filter that has a rating between 1 through 8 can serve its purpose. It just does it at a lower percentage. A rating between 1 and 4 is estimated to catch average-sized particles less than 20% of the time. The particles these can handle include pollen, dust mites, and sanding dust as well as spray paint dust and carpet fibers.

For filters rated between 5 through 8, they are all able to catch:

  • Mold spores
  • Hair spray
  • Fabric protector
  • Cement dust

MERV rating 5 is estimated to catch particles from 20% to 34%, rating 6 from 35% to 49%, and rating 7 from 50% to 69%. MERV rating 8 is estimated to catch particles from 70% to 85%. This is one of the ratings that are most commonly found in residential HVAC systems.

The particles floating in the indoor air of a home are much different from the particles floating around in an office or commercial site. Testing, therefore, takes that into consideration. The allergens floating inside your house also vary by season. Pollen is common as soon as the trees begin to bloom while the winter months see the least number of allergens. The fact that many people keep their windows closed during the winter months plays a role, too.

MERV 8 filters have been around since the 1970s. They are generally 2-inch and pleated. This filter works well with a residential HVAC system. If a unit is experiencing issues that are related to the filter, it is usually because the filter has not been replaced for several months. All the accumulated particles have to be removed at least once after the summer season so that they do not form a clog. The clog could obstruct the air, which is inefficient. In the worst-case scenario, the clog could cause the hardware to overheat and stop working completely.

This filter can successfully capture up to 85% of the particles that are known to trigger respiratory issues such as asthma or allergies. For someone who suffers from those issues, it is a welcome relief. If there are children in your home, it is more important to have a system that can remove at least 85% of those particles. Children’s brains and vital organs such as the lungs are still developing well beyond the toddler years. The longer their lungs can remain healthy, the less likely they are to experience respiratory issues. Some people are prone to asthma or allergies, but if they are kept away from the triggers, it could remain dormant.

These filters are also inexpensive and can easily be serviced by a residential HVAC technician. Some can last up to six months. On the low end, they are good for three months.

MERV Rating 9-12

Filters with a rating of 9 through 12 are deemed to be able to capture:

  • Humidifier dust
  • Lead dust
  • Auto emissions
  • Milled flour

The particle size can be as small as 1.0 – 3.0 Micron. This means they capture those on top of particles that are 0.3 micrometers – 10 micrometers.

From 9 through 11, they have an 85% success rate for particles that are 0.3 micrometers – 10 micrometers. Rating 12 can typically achieve a 90% success rate. For particles that are 1.0 – 3.0 Micron, MERV 9 has a success rate of less than 50%, 10 is 50% to 64% and 11 is 65% to 79%. Rating 12 is the best in this bracket with a rate of 80% to 89%.

The filters that fall into this bracket are usually used as pre-filters or final filters. Hospital laboratories, commercial buildings, and superior residential buildings often have the HVAC systems that can handle this more efficient filter.

MERV Rating 13 – 16

Air filters in this rating bracket are used for heavy-duty jobs and environments. They are used as final filters in environments such as general surgery, superior commercial buildings, and hospital inpatient care as well as smoking lounges. They can capture particles as small as 0.3 – 1.0 Micron. This includes bacteria, tobacco smoke, and droplet nuclei aka a sneeze. This is the best of the best. All of them have a success rate of 90% for 1.0 – 3.0 Micron and 3.0 – 10.0 Micron. They vary for the 0.3 – 1.0 Micron particles.

A MERV 13 can achieve up to 75% success rate. While 14 has a 75% – 84% rate, 15 has an 85% – 94% rate and 16 scores a 95% or better rate.

MERV 17 – 20 also exists, but these are the big boys of air filters. They are usually found in orthopedic surgery rooms, pharmaceutical manufacturing facilities, and rooms that have radioactive materials. These filters can capture microscopic allergens, odors, and Radon progeny as well as face powder, carbon dust, and copier toner. They are placed in HVAC systems that have comparable power and efficiency.

To find out if your air filters are good quality according to the MERV air filter ratings, contact us at Hoff Heating & AC in O’Fallon, MO, today. We provide a variety of services related to heating and cooling repair, maintenance, and replacement as well as indoor air quality. We look forward to hearing from you.