Ever gone to look for a filter for your air conditioner and been completely daunted by the seemingly endless selection. Not only does the size of the filter matter, but then you have different ratings. And it seems that brands have different ratings for their filters! Well this is partially true. There is actually some uniformity of the rating systems used. And that is what this blog post is about.
According to Services Champions, (servicechampions.com), there are five (5) ratings you will come across:
1) Microns and particulate matter
5) HVAC air filters dimensions
Most filters homeowners will come across are going to be "pleated," they have a white wavy material that is held together by small metal webbing. What drives the efficiency of the filters is how much of a given particulate matter is removed by the filter. Efficiency of the filter is not related to the efficiency of the HVAC unit. The reason for this is because your HVAC unit requires air circulation to maintain its efficiency. So as you get thicker and thicker filters that remove smaller and smaller particulates, you are intact restricting airflow to the HVAC system. So it is important as we go through the various "levels" of filtration, that you keep in mind, that these levels can have and adverse affect on your HVAC system.
It is also good to know that the dimensions of your filters will be in LxWxH and are printed directly on the box and air filter.
Understanding Particulate Matter and Microns:
So what is a micron? Also known as a micrometer, it is a unit of measure equal to one millionth of a meter. For our purposes, it is the measurement used for particulates. According to the Service Champions website, "the human eye cannot see anything smaller than 40 microns in size." So basically if it smaller than human hair (about 50 microns) your not going to see the particulates being taken out of the air. Fumes are less than one micron.
MERV Ratings for HVAC filters
MERV stands for Minimum Efficiency Reporting Value. This is a standard rating system used by the HVAC industry. This was designed by the American Society of Heating, Refrigerating and Air Conditioning Engineers.
MERV Ratings range from 1-20. We will only focus on 1-16 for this post as it is the only range really needed by homeowners. The higher the rating, the more efficient the filters are at removing particulates (but also restricting airflow). MERV ratings tell you the minimum efficiency, so the very least performance you can expect.
MERV ratings 1-4:
Carpet and textile fibers
MERV ratings 5-8:
Hair Sprays and fabric protectors
Cement and pudding mixes
Humidifier dust (mineral dust)
Emissions and fumes
FPR Ratings for HVAC filters
FPR stands for Filter Performance Rating. This rating was developed by The Home Depot and used for the brands of HVAC filters sold in its stores. The ratings are number and color coded. It starts at 4 ("GOOD") and goes to 10 ("PREMIUM").
According to The Home Depot:
FPR4 remove particles like:
FPR7 additionally remove:
FPR9 additionally remove:
FPR10 additionally remove:
These ratings are only used by The Home Depot, so you most likely not see these ratings if you are purchasing your air filters outside of that store.
MPR Ratings for HVAC filters
MPR stands for Micro-particle performance rating. This as created by 3M for their HVAC air filters. It is expressed as a number and it indicates the efficiency of removing particles that are between 0.30 and 1.0 micron in size. This range was used because 99% of all airborne particulate matter falls within this range.
MPR300 (equal to MERV 6)
Captures about 35% of all indoor air pollutants between 3 and 10 microns, including large household allergens like Dust.
MPR600 (equal to MERV 7)
Catches up to 65% of particles between 3 and 10 microns. Includes Dust mites, pollen and debris.
MPR1000 (equal to MERV11)
Catch up to 80% of particles between 3 and 10 microns. They are capable of catching larger allergens as well as smaller particulate matter like smog and bacteria.
MPR1200 (equal to MERV11)
Removes 85% of all airborne particles between 3 and 10 microns. Additionally they remove odors caused by cooking oils, cleaning chemicals, smoking, VOCs and pets or animals.
MPR1500 (equal to MERV 11)
Removes up to 90% of all indoor air particles between 3 and 10 microns. This filters capture larger and smaller allergens, and even particles that carry odors and viruses.
MPR1900 (equal to MERV12)
Remove up to 93% of all airborne particles between 3 and 10 microns. They can remove larger allergen particles like microbiological growth, pet dander and other household particles. In addition they remove smaller allergens like viruses and bacteria.
MPR2200 (equal to MERV 13)
These HVAC filters remove up to 94% of all airborne particles between 3 and 10 microns. They remove particles like viruses, odors, smoke, smog and bacteria.
MPR2800 (equal to MERV 14)
These HVAC filters remove up to 97% of all airborne particles between 3 and 10 microns. They remove all bothersome indoor air pollutants at an increased efficiency rating.
All of these HVAC filters are meant to remove particles from the air that is returned to the HVAC Unit so that dust and particulates are not recirculated through the system or even in some cases to prevent large particles from damaging the mechanical parts of the system. It is tempting to think that by purchasing the highest rated filter would be the best for your home. But as mentioned before, air is an essential part to your HVAC system functioning properly. The more you restrict the flow of air, the harder your system has to work to get the air cooled or heated. The higher the filter rating, the harder it is for air to pass through, so at a certain point, you will be actually hurting your HVAC system and your energy efficiency. It is recommended that you consult your manufacturer's manual to see the recommended ratings for air filters for your system. Unless your home is a hospital setting, you will most likely not have an HVAC system that will be able to utilize filters that are rated more than MERV 9 or 10. The reason is due to the required amount of air needed to circulate through the system. If you have ever had a AC unit freeze up on you it was most likely because there was not enough air circulating and so the compressor had to work extra hard and ended up freezing.