Our HVAC equipment controls the air temperature in our homes, but the quality of air that it circulates depends in part on the type of air filter that we use. Of course we all want to keep the air in our homes as clean as possible. It can be complicated to figure out which filter is the best for our specific needs.
About MERV Ratings
What is MERV?
To help you navigate the world of air quality, air filters are all given a national, industry standard rating called a MERV rating. MERV stands for Minimum Efficiency Reporting Value. It’s a 1 to 20 scale that tells you what size particles the filter will capture. A higher MERV rating means that it captures smaller particles.
If you want to get technical, MERV ratings are calculated by testing how many particles of different sizes can travel through the filter. Raters ask questions like: “When we spray a can of hairspray at this filter, how many of the particles make it through”? The number is calculated into a percentage and placed in a MERV rating category. Filters with higher numbers are considered higher quality filters. Typically, filters with higher MERV ratings cost quite a bit more. Some last longer.
MERV Rating Options – What You Get for Your MERV
Let’s take a look at the range of filter options:
MERV 1 to 4 are spun fiberglass filters. They are basic, cheap and not especially effective. Low-MERV filters are able to block out things like large particles like pollen, sawdust, pet hair and dust mites. They are the most affordable option but have a short life span and need to be changed more often. These filters are not sufficient to filter the air in your whole home or trap finer particles such as pet dander, smoke, food smells and other serious allergens. If you have allergies, asthma, COPD or other significant respiratory issue, then a cheap fiberglass filter is not a good option.
The Environmental Protection Agency, or EPA, says these cheap fiberglass filters will trap just 20% of the pollution/allergen particles between 0.3 and 10 microns (µm). that might be circulating through your home. That’s not very effective. These low-cost air filters run less than $5 each.
MERV 5 to 8 are the type of filters you’ll find in most residential and commercial buildings. They can capture additional things such as mold spores, and aerosol sprays like cleaning chemicals. Start at this level if you have any sort of breathing issues. The EPA rates them to capture about 50% of harmful pollutants between 0.3 and 10 microns. Stop in the air filter aisle of your local hardware or home improvement store, and you’ll find a number of options like these from Amazon. Cost is around $6-$10 each.
MERV 9 to 12 are commonly found in places that need extra filtration due to the presence of small-particle pollutants. But at this MERV rating, the efficiency of your HVAC equipment might begin to suffer. This issue is explored below, but the basic idea is that the thicker and denser the filter is, the harder it is to pull air through it. This will make your air handler work a little harder.
MERV 9 to 12 filters provide the next level of purification for an increased cost. They capture all of the larger particles mentioned above as well as lead, coal and fine dust. On the technical side, the EPA rates filters in this range to trap up to 1.0 - 3.0 80% - 89.9%, 3.0 - 10.0 90% or greater. Cost is a little higher – up to $15 each. You’ll save money if you buy them in a pack of 5 or more.
MERV 13 to 16 are most likely to be found in areas that need to be very clean such as hospitals. They can filter out extremely small particles such as smoke and fumes. They will even catch droplets from a sneeze! While filters with effectiveness in this range are available for residential use, they are too thick to fit into the standard air filter slot. You would have to hire an HVAC technician to construct a slot in your ductwork to house them. Cost is about $70 to $90 per filter.
MERV 17 to 20 are typically used in highly polluted areas or areas that need to have pristine air quality. You’ll find them in places such as surgery rooms and in places with radioactive chemicals. On top of all of the larger particles, these filters can block microscopic allergens, carbon dust, and virus carriers. They’re rarely used in residential settings.
What MERV Rating Should I Use?
To find the best MERV rated filter for your specific equipment, you’ll need to consider a few key factors. Think about what type of air pollutants are most common in your home. Do you have pets? If you’re a hobby woodworker or painter, you’ll have extra particles and fumes travelling through the air in your spaces.
Do you live in an older home with a damp crawl space? Do you smoke in your home? Keep in mind that some heating sources, such as wood stoves and pellet stoves, create more pollutants and dust than other types of heating equipment.
After you think about what is in your home, consider who lives there. Parents with small children often want to make sure that their air quality in their home is clean enough for developing lungs. People with pet allergies or intense seasonal allergies need their home to be a safe space, free of irritants. All of these factors will impact what quality air filtration you need in your home.
Filters with a MERV rating between 6 and 13 will get the job done in most homes. Filters within this range will last up to six months before they need to be replaced. Let’s take a look at some recommended MERV values for homeowners:
MERV 6: This is the most basic level of filtration for a home. It captures bigger things such as pet hair, pollen and lint. A filter with a MERV 6 rating is the cheapest option for basic home filtration. If you don’t have breathing issues and aren’t creating pollution in your home, then you’ll probably be OK with a 6 MERV to 8 MERV filter.
MERV 8: This rating is the basic recommended filter for homes with pets. It still doesn't filter as many allergens and pollutants as filters at the top of the price range, but it can still handle pet dander, dust mites, and mold.
MERV 11: MERV 11 filters cost more but typically have a longer lifespan than those with a lower rating. They’re best for homeowners who have allergies or who are serious about filtering out their pet dander or other allergens.
MERV 13: Filters with a MERV 13 rating are able to capture viruses, bacteria, smoke, smog and other particles. They’re the best choice for polluted areas. This is the highest rated filter that you’ll easily find in your local hardware stores. For anything higher, you’ll need to search at a more specialized retailer.
Is Higher MERV Always Better?
No. As mentioned above, it really depends on what your needs and goals are.
You might think that it’s best to just buy the filter with the highest possible rating, but that’s not always the case. You should always check the unit you’re using. See if your equipment has a maximum MERV rating. Choosing a filter with MERV rating that’s too high for your unit can cause it to work too hard and wear out your equipment faster.
As one retailer says, “When selecting the right filter for your application, higher is not always better. Using an air filter with a MERV rating higher than what your furnace or air conditioner manufacturer recommends can actually impair its performance.
The smaller pores in more highly rated air filters create resistance to air flow, and if the filter is used in an HVAC system that is not designed to handle this resistance, it can lower the system's efficiency, decrease indoor air quality, and put strain on the system's fan.”
What About Other Air Filter Ratings?
The other ratings you might see as you shop for air handler filters are MPR and FPR. MPR stands for Microparticle Performance Rating and is a rating invented by 3M for its popular Filtrete brand of air filters. FPR stands for Filter Performance Rating and is a rating created for Honeywell air filters. The PickHVAC guide explains the similarities and differences in the ratings.
We’ve done a separate guide called MERV vs. MPR vs. FPR: What Air Filter Rating Should I Choose?