Removing pollutants from the air in your home means you and your family can breathe cleaner. It also means you can breathe easier knowing that your heating and cooling system isn't being overworked and raising your utility bills. That's because dirt can cause furnace or air conditioner failure and an AC or furnace filter's main job is to stop dirt and dust from entering your equipment.
Unfortunately, filters have a short lifespan because they fill up quickly with all the pollutants, dust particles and allergens in the air.
MERV ratings
Selecting the right air filter for your home can be a confusing process, with so many products available in the market. Being able to choose the best air filter takes a basic understanding of MERV ratings (Minimum Efficiency Reporting Value), and how they reflect the quality of the filter.
An air filter's MERV indicates its ability to capture airborne particles while air is flowing through your heating or cooling system. For residential purposes, MERV ratings range from 1-16. Generally speaking, the cheaper the filter is, the lower the MERV number is. Air filters with lower MERV ratings will remove a smaller percentage of pollutants from your home. Filters with a MERV between 7 and 12 are considered good quality.
Although filters with a higher micron/MERV rating cannot eliminate the need for dusting, they can help reduce the need.
Listed below are some of the most common types of residential HVAC air filters, and the MERV rating you can expect to find on each one:
Fiberglass air filters
Often available for less than $10, fiberglass air filters have thin flat surfaces that trap particles and clean the air but only catch up to 20% of pollutants ranging from 3 to 10 microns, removing mainly larger particles like dust, lint and small insects. Originally designed to protect heating and air conditioning equipment, these filters are less effective when it comes to improving indoor air quality. It's recommended to replace them once every month.
MERV Rating: 1-4
Electrostatic air filters
Disposable electrostatic air filters contain self-charging electrostatic cotton or paper fibers that attract and trap small particles. The electrostatic charge is created by air flowing through a maze of the static-prone fibers. These filters are good for homes with children, pets or smokers, and are affordable in standard sizes. It is recommended to replace disposable electrostatic filters every three months to keep your home free of airborne allergens.
MERV Rating: 6-8
Pleated air filters
A step up from and better investment than fiberglass air filters and more popular than electrostatic air filters, disposable pleated filters capture between 70-90% of the airborne pollutants in your home between 3 and 10 microns. Made from polyester or cotton paper, – the more pleats, the greater the coverage. Pleated air filters can be purchased for around $15 each or less, and like electrostatic air filters, only need to be switched out every three months.
MERV Rating: 6-13
High-efficiency air filters
High-efficiency air filters are generally considered the most effective filters for most residential HVAC systems. Some are made from 4-5” pleated synthetic cotton attached to a rigid metal grid, these filters can trap up to 95% of particles down to 0.3 microns in size including very tiny dust particles, pollen, mold and other irritants. There are also UV filters, which are high-end filters that contain all the components of a traditional but with a germ killing UV light.
Using an HVAC filter ranging between a 9-12 MERV rating is an excellent means of controlling dust and other particles.
MERV Rating: 9-16
Another important aspect to consider when choosing a filter is airflow restriction or static pressure drop across the filter. Generally filters with a higher MERV rating have a more profound effect on airflow. Choosing a filter with too much restriction to airflow will cause your furnace to work harder and could increase your energy bills and lead to increased equipment failure.
Another rating scale for furnace is MPR (Microparticle Performance Rating).
For most residential homes, a filter with an MPR 600 rating will be sufficient to filter out most dust, pollen, and mold.
If you’re familiar with the MERV rating scale, then an MPR 600 filter is roughly equivalent to a MERV 7 air filter. However, an MPR 600 air filter exceeds the requirements of MERV 7 air filters since they are tested to filter out more microparticles than a standard MERV 7 filter.
If you have allergies or pets, I recommend using a filter with an MPR 1000 rating to filter out small particles such as pet dander, fine dust, and smoke.
MPR 1000 air filters are roughly equivalent to a MERV 11 air filter. However, like MPR 600 air filters, MPR 1000 air filters will filter out more microparticles than their MERV-rated counterparts.
Higher-rated MPR filters are more efficient at filtering out small particles. But this doesn’t mean that you should automatically go for the highest-rated MPR filter for your home’s HVAC system.
One reason is that the more efficient a filter is, the more expensive it will be. If you are replacing the highest-rated MPR filters every month, then your filter bill will add up quickly.
Another reason is that filters with high-efficiency ratings tend to impede airflow. While this isn’t as much of a problem as it was in the past (due to modern engineering), it is definitely still a point to consider. Especially if you’re trying to keep your energy costs down.
One final reason is that most people simply don’t need the level of air filtration that high MPR ratings provide. You’ll be fine with a moderate-efficiency air filter unless you suffer from chronic allergies or your immune system is compromised.
What is the MPR rating scale?
The Microparticle Performance Rating (MPR) is an air filter rating scale that is designed by the 3M company. The main purpose of the MPR system is to rate an air filter’s ability to filter out microparticles.
The MPR rating scale focuses on the smallest particles measured by the MERV scale – E1 particles. E1 particles are particles that have a diameter between 0.3 and 1.0 microns. I’ll talk more about E1 particles later.
The MPR system is different than the MERV scale in that it focuses on a filter’s ability to filter out microparticles. For this reason, most MPR-rated filters capture more microparticles than the equivalent MERV-rated filter.
Even the lowest-rated MPR 300 filters capture 12% of E1 microparticles. These particles are not even measured by the MERV rating scale until MERV 10.
Is a higher MPR rating better?
Just because higher MPR-rated filters capture more particles, doesn’t mean that you should go for the highest MPR rating that you can find. Using a filter with higher filtration efficiency will add more airflow restriction to your HVAC system, possibly prolonging runtimes and using more energy.
The best thing to do is to use a filter with a sufficient rating to filter out particulates, but not high enough to overstress your furnace or AC.
A good MPR rating to start at is MPR 600. Filters with an MPR 600 rating strike a good balance between filtration efficiency and airflow.
If you are susceptible to allergens such as fine dust or pollen, moving up to an MPR 1000 filter is the next step in air filtration efficiency.
It has been shown that filters with higher efficiency ratings tend to block some airflow. In the past, this was definitely the case. But this assumption is not entirely true anymore. Modern pleated filters utilize large surface areas to maximize airflow through the filter.
When considering the airflow impact that a filter has on your HVAC system, there are many factors at play- such as the type of fan motor and the dimensions of the air filter. Check out our article on how MERV ratings affect airflow for more information.
Comparison of air filter MPR ratings
The MPR system rates air filters on a scale of 100 to 2800 based on their ability to filter out microparticles. The higher the MPR rating, the more particles a filter blocks. Filters with a low MPR rating are only able to filter out large particles such as lint and hair. Higher MPR ratings bring more air filtration, especially with small microscopic particles.
Starting at MPR 100, these filters represent the most basic pleated filters. MPR 100 to 300 filters are made for filtering out basic dust and dust mites. They are equivalent to about a MERV 5 rating.
Stepping up to MPR 600, these filters provide a standard level of filtration. In addition to dust, MPR 600 filters are able to filter out mold spores and pollen. These filters are sufficient for most residential homes since they provide a decent level of filtration and won’t impede very much airflow.
MPR 1000 filters step up into allergy-fighting territory. These filters are good for those that suffer from allergies since they provide a higher level of filtration against pet dander and smoke. These are a good choice if you need an increased level of protection from seasonal allergies or excessive dust.
MPR 1500 filters take everything a step further and are able to filter out some bacteria and viruses. These filters are considered a MERV 12 but they are able to capture 19% more E1 particles than a standard MERV 12 filter.
MPR 2200 filters are among the strongest filters on the MPR rating scale (only MPR 2800 is stronger). MPR 2200 filters are able to capture soot, exhaust particles, and everything else that lower-rated filters are able to. These filters are considered a MERV 13 but they are able to capture 19% more E1 particles than a standard MERV 13 filter.
Air filter particle sizes: E1 vs E2 vs E3 particles
Air filters are tested by measuring the number of particles that they block. The particles that are tested with air filters are classified by their size into three different categories:
- E1 particles are particles that are 0.3 to 1.0 microns in diameter. These are the smallest type of particles tested with air filters. E1 particles represent small microscopic particles such as smoke, haze, bacteria, and some viruses.
- E2 particles are 1.0 to 3.0 microns in diameter. Pet dander and E. coli fall into the E2 particle range. PM2.5 particles begin in the E2 range since they are smaller than 2.5 micrometers.
- E3 particles are 3.0 to 10 microns in diameter. Most household dust, pollen, and mold fall into this range. For comparison, the diameter of a human hair is around 50 to 70 microns, at least 5 times larger than the diameter of the largest E3 particle.
Air filters with higher MPR ratings will block more particles than air filters with lower MPR ratings. For instance, an MPR 1000 filter will block 41% of E1, 77% of E2, and 88% of E3 particles.
