Joseph L. Sbarra, CIHCertified Industrial Hygienist with > 35 years experience   So it's time to replace the air filter to your furnace or HVAC (Heating, Ventilation, and Air Conditioning) system. That’s great, because an air filter can have a significant and positive impact on the air quality in your home. I’m sure that you have noticed that there are lots of choices out there, and it’s really confusing. Also, what do MERV, FPR, and MPR mean anyway?? Let’s take a look... Air Filter Rating Systems MERV, FPR, and MPR are rating systems for air filters, including those used in household furnaces and HVAC systems. The good news is that you really only need to pay attention to one of them: MERV There is an organization called the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). They have a standard called “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size” (ASHRAE 55-2017). Translation: It is standardized method for evaluating how effective air filters are at stopping different sizes of particles. It is the only scientifically recognized and standardized rating system for air filter efficiency that exists in the United States. MERV (Minimum Efficiency Reporting Value) is a rating system that is part of the standard. Essentially, the higher the MERV rating for an air filter, the higher the efficiency of particle removal. We’ll talk more about MERV in a minute, but I want to discuss FPR and MPR. FPR stands for Filter Performance Rating, and it is a rating system developed by one of the large home improvement stores; it appears to be more marketing-based than science-based. It is unclear what methods have been utilized for this rating system, and it is not available for scientific review. MPR stands for Micro-particle Performance Rating and it is a rating system developed by 3M. This system likely has some science behind it, but it is exclusive to 3M and nobody else is using it. My advice: If an air filter manufacturer is not going to use the MERV rating system that is recognized nationally, then simply don’t use their products! The MERV Rating System The MERV system rates removal efficiency by particle size. The MERV system goes from 1→ 16. Below is a table that provides a basic summary of the MERV ratings, removal efficiency by particle size and typical applications:1  Table Note: µm = micrometer or micron. 1 µm = .001 meters (one one-thousandth of a meter). The table above is is a simplified summary of information from the ASHRAE standard; what is not included are the overlapping efficiencies by particle sizes. For instance, a MERV 12 air filter has a 20% removal efficiency for particles in the 0.3 - 1.0 µm range. You can see that the higher the MERV rating, the more efficient a filter will be at removing smaller particles. You can also see that the removal efficiency varies greatly within each of the four (4) major groups of particle size ranges. For example, for the 1.0 - 3.0 µm range, a MERV 8 air filter only removes 35% of the particles, whereas the MERV 12 removes 80% of the particles. Also, look at the typical application descriptions as they relate to residential homes:
Choosing a MERV Rating for Your Air Filter There are several things to consider when choosing what MERV rating you want for the air filter in your home, these include: Filter Cost - the higher the MERV rating, the higher the cost of the filter. Also, you will also have to replace higher MERV rated filters more often as they trap more particles, and can become overloaded faster than lower-rated filters. Health - do your or someone in your family have allergies or respiratory problems? Indoor Air Quality - do you have any of the following that can impact the air quality inside your home?
Environmental Factors - do you live in an area where outdoor dust levels are high, such as city or industrial area? Furnace/HVAC System Age and Condition - newer systems are generally more efficient than older systems and can generally handle higher MERV-rated filters. Also, a well maintained system will be able to handle the higher rated filters better than a system that is not maintained. Remember, an overloaded filter can put a lot of strain on the blower fan of your furnace/HVAC. Note: If you are considering using an air filter with a MERV rating > 8, check your furnace/HVAC unit manual to see if there are recommendations on maximum MERV ratings for air filters for the system. If not, I recommend that you buy one (1) air filter and have your HVAC technician take static pressure readings inside the unit to ensure that the furnace/HVAC unit is within operational range. Tips Buy On-line and Avoid Home Improvement Chain Stores- You will certainly pay less on-line compared to buying from any of the large home improvement stores. In my home, we use MERV 12 filters for our HVAC system. We bought a package of 6 online, at a cost of $7.45 each. I checked on-line at the home improvement stores for comparison: their filters (similar to MERV 12) cost $13.60 - 15.97 each (that price includes a 20% discount for ordering at least 4). Beware of Advertising Claims - there are lots of filters out there claiming to remove many things. While there is a grain of truth to these claims, you are really being mislead. For instance, there are MERV 11 and 12 filter manufacturers claiming to remove bacteria, droplets from sneezing, and cigarette smoke (which are all from the smallest particle range, 0.3 - 1.0 µm). This claim is true, but there is only a 20% removal efficiency for the MERV 11 and a 35% removal efficiency for the MERV 12. Odors - there are some manufacturers claiming that their air filters can remove odors with baking soda or activated carbon/charcoal. Volatile Organic Compounds - some manufacturers claim that their air filters can remove volatile organic compounds with activated carbon/charcoal. Neither odors or volatile organic compounds are test parameters included in the MERV rating system. Additionally, the manufacturers do not provide any scientific evidence to support these claims, so use your judgment. Good luck with selecting the right air filter for your home and stay safe and healthy! Footnotes: 1 - Summary of information from ANSI/ASHRAE standard: 52.2-2017 “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size”.
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Joseph L. Sbarra, CIH, CSP
1/19/2023 10:58:01 am
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