The air filter is an extremely important part of any HVAC system. Contrary to what many people think, the primary purpose of the air filter is to prevent dust and debris from getting inside the system and damaging its components. Depending on the type and quality of the filter, it can also help to improve indoor air quality by filtering out pollutants, allergens and contaminants from the air. At Green Energy Mechanical Inc, we regularly have clients asking us which type of filter they should use. Therefore, we’ve produced this guide so that you can better understand air filter ratings and more easily choose the best filter for your HVAC system.

How Air Filters Are Rated

Most HVAC air filters are rated using the MERV (Minimum Efficiency Reporting Value) scale, which measures how efficient the filter is at trapping airborne particles of varying sizes from 10 microns down to 0.3 microns. The scale starts at MERV 1, which is the least efficient, and goes all the way up to MERV 20. To make matters slightly more confusing, anything from MERV 17 and above is considered a HEPA (High-Efficiency Particulate Air) filter. To help clear things up, let’s look at exactly what these numbers mean and why HEPA filters should never be used in a residential HVAC system.

The MERV Scale Explained

The MERV scale is usually broken up into several segments. At the lowest end of the range, you have MERV 1 to MERV 4 filters. These filters are usually made from aluminum or fiberglass mesh and are only somewhat effective at trapping dirt, dust and other large airborne particles. In most cases, these filters will capture less than 20% of the largest particles from 10 down to 3 microns and 0% of anything smaller. For this reason, these lower-rated filters are generally only ever used for window or portable AC units as they simply aren’t effective enough to prevent damage to your HVAC system.

MERV 5 to MERV 7 filters are generally the bare minimum for residential HVAC systems. These filters are much more effective at trapping larger particles like dust, and they are also somewhat effective at trapping some smaller airborne particles like pollen, dust mites, mold spores, aerosol sprays and some chemical pollutants. These filters will typically trap anywhere from 20%-70% of the largest particles and at least some smaller particles.

MERV 8 to 13 filters provide much better filtration for residential HVAC systems, trapping anywhere from 70%-85% of the largest particles and up to 50% of particles between 1 and 3 microns. This includes things like lead dust, flour and even some VOCs (volatile organic compounds) like gas fumes and formaldehyde.

MERV 11 to MERV 13 filters provide the highest level of filtration for residential HVAC systems, but they are much more commonly used in commercial HVAC systems. These filters will generally trap up to 90% of particles between 1 and 10 microns, and MERV 13 filters can even trap up to 75% of the smallest particles between 0.3 and 1 microns. While this level of filtration does have its uses, it is generally unnecessary outside of certain industrial and commercial settings. In fact, even hospitals rarely use anything above MERV 12 or MERV 13 for their general public areas.

MERV 14 to MERV 16 filters provide the highest level of filtration possible outside of a true HEPA filter. This type of filter is generally only used in certain industrial or laboratory settings as well as hospital inpatient rooms and general surgical rooms.

Anything above MERV 16 is a true HEPA filter. While you can find HEPA filters in some air purifiers and vacuum cleaners, they really only have very limited use. In fact, it is extremely rare to find HEPA filters used except in laboratory or some surgical settings that require an extremely sterile environment. Part of the reason that HEPA filters are so very rarely used is that they are extremely restrictive in terms of airflow. It requires an incredibly powerful HVAC system to be able to properly draw air in through a HEPA filter. If the system isn’t powerful enough, it simply won’t be able to heat and cool properly as it won’t have enough airflow.

Choosing the Right Air Filter for Your HVAC System

For residential HVAC systems, you should generally always stick with something between MERV 5 and MERV 12 at the very most. That being said, many residential HVAC systems aren’t powerful enough to handle even a MERV 12 filter. If you attempt to use too efficient a filter, it can lead to a huge number of problems with your heating and cooling systems as it will be too restrictive for proper airflow.

In this situation, you are likely to experience issues with insufficient heating and cooling, which means your furnace or AC will have to run much longer and much more frequently. In turn, this can lead to greater wear and tear on your HVAC components, more frequent repairs, and a potentially shortened lifespan for your HVAC equipment.

If your main concern is protecting your HVAC system from damage, anything from MERV 5 to MERV 8 should be more than sufficient. On the other hand, if you are concerned about indoor air quality, you may consider upgrading to a MERV 10 or MERV 11 filter. These types of filters can also be a great choice for anyone who suffers from serious allergies or any respiratory problems like asthma or COPD. This is because they will also work to remove most airborne allergens and other contaminants from the air to allow you to breathe easier and more freely.

Other Rating Systems

Depending on the brand of filter and where you buy it from, its efficiency may be measured using something other than the MERV scale. 3M and Home Depot have their own rating scales for residential air filters, and this can add to the confusion.

3M filters are rated using the MPR (Micro-Particle Performance Rating) scale, which only measures how efficient the filter is at trapping particles smaller than 1 micron. This scale ranges from MPR 100 to MPR 2800, which is essentially equivalent to MERV 6 and MERV 13.

Home Depot filters are rated using the FPR (Filter Performance Rating) scale, which is similar to MERV in that it looks at particles of varying sizes. This scale ranges from FPR 5 to FPR 10, which equates to MERV 8 and MERV 13.

Professional HVAC Services and Support

If you’re still struggling to determine which is the best air filter for your home’s HVAC system, the team at Green Energy Mechanical Inc is here to help. We can evaluate your HVAC system to determine if it is powerful enough to handle a more efficient filter or if you’re better off sticking with a more basic level of filtration. As a full-service HVAC contractor, we can also handle any of your heating and cooling repair, maintenance, and installation needs. We work on all makes, models, and types of HVAC equipment including furnaces, central air conditioners, boilers, ductless mini-splits, and heat pumps. We are conveniently located in Canton and proudly serve customers throughout Norfolk County and the surrounding areas. For more information on our range of services or to schedule an appointment, give us a call today.

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