Having adequate air filtration is essential for every home. Not only does the filter in your HVAC system help prevent it from getting damaged, but it also works to overcome air quality issues. This is so that the air in your home is cleaner. That said, the overall effect on indoor air quality depends on which type of filter you use. Knowing which filter is the best choice isn’t always easy, but this guide will explain the differences between the various types so that you can make a more informed choice.
An Overview of MERV Ratings and What They Indicate
The first thing to understand about air filters is that MERV is merely a rating scale that tells you how efficient any filter is. MERV stands for minimum efficiency reporting value and is a metric that expresses how well an air filter filters out particles from 10 down to 0.3 microns in size. These tiny particles are of the biggest concern in terms of indoor air quality since they are small enough to get deep inside your lungs when breathed in.
The scale starts at MERV 1, which is the least efficient, and goes all the way up to MERV 16. It technically goes up to MERV 20. However, anything from MERV 17 and above is only used for very specific applications like in pharmaceutical manufacturing or places that deal with radioactive or carcinogenic materials. MERV 1 filters are generally only designed for use in window air conditioners. In terms of residential HVAC air filters, you rarely find anything under MERV 6-8.
There are some MERV 3-4 fiberglass or aluminum mesh filters on the market. However, these aren’t recommended since they aren’t nearly efficient enough to keep dust and debris from getting inside an HVAC system. For standard 1-inch HVAC air filters, you also rarely ever see anything above MERV 13. If you want to go any higher, generally your only option is to retrofit your HVAC to accommodate a thicker “media” filter. Or you could install some type of whole-home filtration or purification system.
While MERV is the most common air filter rating scale, it’s not the only one you may encounter. The two other ones some manufacturers and retailers use are MPR (microparticle performance rating) and FPR (filter performance rating). Along with a MERV, MRP or FPR rating, you’ll also often see filters labeled Good, Better, Best and Premium or, sometimes, Standard, Superior and Optimal. Due to the differences in how each scale works, it’s difficult to compare each rating like to like. Nonetheless, below you’ll find at least an approximation of what FPR and MPR ratings are comparable to on the MERV scale.
FPR Compared to MERV
- FPR 4-5 = MERV 6-8
- FPR 6-7 = MERV 8-11
- FPR 8-9 = MERV 11
- FPR 10 = MERV 13
MPR Compared to MERV
- MPR 600-1,000 = MERV 8
- MPR 1,200-1,900 = MERV 11
- MPR 1,900-2,800 = MERV 13
What Are HEPA Filters?
Air filters from MERV 17 to MERV 20 are technically HEPA filters. However, there are different testing protocols used in order to be classified as a true HEPA filter. All HEPA filters have to be efficient enough to trap at least 99.7% of particles down to 0.3 microns in size. That makes them at least 50% more efficient than the highest MERV 16 filters.
HEPA filters are primarily used in situations that require an extremely high level of filtration. In fact, even hospitals typically only use MERV 14-16 filters. They only have HEPA filters in places that need to be extremely sterile, such as operating theaters and intensive care units. Nonetheless, people with extremely severe allergies or who are immunocompromised may benefit from installing a whole-home air purification system that uses a HEPA filter. You’ll also find some HEPA filter vacuums designed for allergy sufferers and also used in construction and other specific applications.
The one thing to note about HEPA filtration systems is that they can only be installed onto a central HVAC system via a bypass duct. They also require an internal fan to draw air out of the ductwork and force it through the filter before it then gets blown back into the duct system. The reason is that HEPA filters are extremely restrictive. This means it requires much more force to push air through the filter than even the most powerful residential HVAC blower could ever produce.
How to Know Which Air Filter You Should Use
When it comes to standard 1-inch residential HVAC air filters, almost every expert will tell you to stick with something between MERV 8 and MERV 13. Anything below MERV 8 isn’t recommended since it will allow quite a bit of dust and other particles to get inside your HVAC system. That can result in damage, poor performance and decreased energy efficiency. Anything above MERV 12-13 is also not recommended for a residential HVAC system. Some systems can’t even handle anything above MERV 10 without performing much more poorly than they should.
The issue with using a filter that is too efficient is that it makes it extremely difficult for the blower to draw sufficient air through the filter and into your furnace or AC air handler. That means your heating and cooling performance will be greatly decreased and your HVAC will consume far more energy. The added strain from using a filter that is too efficient also leads to greater wear and tear and will almost always end up shortening the lifespan of your HVAC system. In fact, using too efficient of a filter essentially has the same effect as never changing the filter at all and running your HVAC when the filter is extremely clogged.
Commercial and industrial systems can handle more efficient filters with no issues, but residential systems end up struggling mightily due to how restrictive the more efficient filters are. That’s why you need to upgrade to a media filter, air cleaner or some other type of filtration/purification system if you want more effective filtration for your home.
If your main concern is protecting your HVAC, a MERV 8 filter is sufficient since it will trap the majority of dust, lint, hair and other large particles. It will also trap a fairly high percentage of dust mites, pollen, mold spores and even some airborne chemicals. That said, people with any type of health issues or allergies are better off using at least a MERV 10 filter. MERV 12-13 filters are the better choice for immunocompromised individuals since they can typically filter out at least 95% of viruses and bacteria.
The only thing to note if you decide to use a more efficient filter is that you will usually need to replace it more frequently since it will trap far more particles and clog up more quickly. A MERV 8 filter typically only needs to be replaced every two to three months. However, you may have to replace your filter every four to six weeks if it has a higher MERV rating. The only exception is if you use a thicker, MERV 14-16 media filter since these usually only need to be replaced once or twice a year.
Contact Us Today
Since 1998, Oak Island Heating and Air Conditioning has been helping customers throughout the San Marcos area with all of their air conditioning, heating and indoor air quality needs. We’re a family-owned business that is dedicated to providing exceptional home comfort services and top-notch customer service. If you have any questions about which air filter is the right choice for your home or need to schedule an appointment for any HVAC service, contact us today.
