It’s that time again. Your home’s HVAC system needs a replacement air filter and, as you remove the old filter, you take a look at the dirty pleats and consider how well it works. You may tend to go with a MERV 8 filter since it seems to be the most common.
Is a MERV 8 rating enough? Yes. MERV 8 is good enough for air filtration in average residential homes. A MERV 8 filter can stop mold spores, pollen, and most cleaning agents. It is important to note, though, that individual circumstances can require a filter with a higher MERV rating.
In this article, we will explain everything that you need to know about the MERV rating of filters.
What is MERV?
MERV is an acronym for minimum efficiency reporting values. It’s a value rating for describing the effectiveness of air filters.
The American Society of Heating, Refrigeration, and Air Conditioning in Engineers, or the ASHRAE, developed MERV in 1987.
MERV ratings quantify the ability to filter out particles, and the particles in question are between 0.3 and 10 microns (source).
Technical and scientific fields use microns, so they aren’t an everyday measurement. A micron is equal to one-millionth of a meter and, in the Imperial terms, that’s 0.04 thousandths of an inch (source).
MERV is dealing with microscopic particles, and it can be hard to imagine such a minuscule measurement without a bit of perspective.
According to Allergy and Air, here’s how common particulates measure up:
- Spores: 3 – 40 microns
- Mold: 3 – 12 microns
- Bacteria: 0.3 – 60 microns
- Car emissions: 1 – 150 microns
- Oxygen: 0.0005 microns
Let’s put those numbers in perspective; mold and bacteria are larger than oxygen, which is how air filters can work. Air filters allow oxygen through while stopping dangerous particulates in their tracks.
The simplest way to explain MERV is that it measures the size of the holes in an air filter. Ask yourself, “Are the holes too large and allow certain particulates through?” or “Can the filter stop mold, bacteria, and other pathogens?”
For the answer, you turn to MERV ratings, which are a scale from 1 to 20. A higher MERV rating means it can capture and stop more particles before they enter your home’s air.
So why should you care about MERV ratings? Can’t you just grab the first filter you see and call it a day? Technically, nothing is stopping you from doing that, but you should take more consideration into MERV ratings.
Before we can delve deeper into that, we need to discuss air filters in detail.
The Different Types of Filters
Air filters are differentiated by more than just their MERV ratings since manufacturers make their filters from different materials. Here are the main categories of air filter types (source):
- Spun fiberglass filters
- Pleated paper or polyester filters
- Electrostatic filters
- Disposable pleated high MERV filters
- HEPA filters — High-Efficiency Particulate Air
Spun Fiberglass Filters
These are the cheapest air filters on the market. Often, the fiberglass material is a blue color, but they can also be white. Due to the nature of fiberglass, these filters will not be pleated like the rest of the options on this list.
These air filters are found at the bottom of the MERV scale and are somewhere between 1 and 4. They are cheap and disposable, which non-discerning customers like. However, they will not block out harmful particles.
Pleated Paper or Polyester Filters
These are the air-filters with the folds, known as pleats. It’s usually in a cardboard frame with a metal grid.
These filters typically cover MERV ratings from 5 to 8, and they can trap 80 to 95% of typical household allergens and pathogens.
Electrostatic Filters
Remember rubbing your socked feet on the carpet and shocking whoever was nearby? These filters harness that same power. It uses static electricity to attract pesky particulates.
Electrostatic filters range anywhere from MERV 2 to 10. They come in both disposable and reusable versions. The reusable filters can be washed and used again, and they can last up to 8 years.
Disposable Pleated High MERV filters
These pleated air filters are very much like the ones found in the 5 to 8 MERV range. The filler material is folded into pleats and held in a cardboard frame.
The main difference, of course, is that its fibers create smaller holes than those in low MERV filters and can trap more particulates than them.
HEPA Filters
High-efficiency particulate air, or HEPA filters, are the gold standard in air filtration. They are made with twisted glass fibers and were originally created to trap radioactive particles during the Manhattan Project!
A HEPA filter can filter out 99.97% of particles that are 0.3 microns or larger. In other words, it can stop a whole lot of pathogens and allergens.
When a MERV 8 is Enough (and When it Isn’t)
A higher MERV rating means a filter is more effective at trapping the microscopic pathogens and particles we’d prefer not to be breathing in. A filter with a MERV rating of 9 is much more effective than one with a MERV rating of 2.
| MERV Rating | What it Filters Out |
| 1- 4 | Textile fibers, sanding dust, dust mites, pollen |
| 5 – 8 | Mold spores, hair spray, dusting aids |
| 9 – 12 | Auto emissions, welding fumes, lead dust, legionella |
| 13 – 16 | Sneezes, tobacco smoke, bacteria, insecticide dust |
| 17 – 20 | Microscopic allergens, virus carriers, combustion smoke, radon progeny |
If you take a look at the above table, you’ll notice why specific ranges of air filters would be more helpful in different scenarios.
A mechanic’s garage should probably stick with a filter with a MERV rating of 9 to 12. Meanwhile, a laboratory working with radon would need one rated 17 or higher (source).
If you’re shopping in the United States, you’ve probably noticed that MERV 8 filters are the most common on the shelves. They are typically 2-inch and pleated, and they’re the most purchased filter since the 1970s (source).
Everything you see listed for a MERV 8 filter or lower will cover what you’d encounter in your average household. For example, pollen and mold spores are definitely particles you’d want to keep out of your home’s HVAC.
On the other hand, the highest MERV ratings are a bit overkill. The average American home isn’t experiencing a lot of combustion smoke or radon progeny. If your home is for some reason, a MERV rating may be the least of your issues.
In most homes, you’ll find a MERV 8 air filter. Again, it handles the most common air filtration needs of the average house.
It also isn’t too taxing on a typical HVAC system because as MERV increases, the airflow it allows decreases. A filter has to sacrifice some air to block out particles as well.
This is a whole lot of information, but how do you know if a MERV 8 filter is enough for your home? Should you ever go lower? What about a higher MERV? Is that ever the answer?
Sinking to a Low MERV
Yes, the choice of the word “sinking” was intentional. It needs to be clear that you shouldn’t try to lower yourself to a rock bottom MERV filter.
Anything with a MERV 4 or lower is not enough for a residential home’s HVAC. A MERV 4 filter cannot stop mold spores. It can’t even block hair spray.
Low MERV filters perform the bare minimum filtration. They capture pollen and dust mites, and that’s where their usefulness ends.
One HVAC training specialist, Jose De La Partilla, has dubbed these “B&B” filters. He claims the only things these filters can keep out are birds and bricks.
These low MERV filters often tempt homeowners due to their low price. Meanwhile, a MERV 13 filter can be on the more expensive side.
In your air filter shopping trips, you’ve probably never encountered anything packaged with a MERV rating of 1-4, so how can you know if it’s a MERV rating that low?
Filters with MERV ratings of 1 – 4 typically don’t advertise it because it’s not much of a selling point. If you find yourself considering a cheap filter will no MERV rating, put it back (source).
Remember, readers: you get what you pay for. The quality of the air you breathe daily is worth more.
Going High MERV
A MERV 8 filter is enough for the average home because these filters cover common allergens like pollen and mold. They also block products typically used in homes, like cleaning products and hair spray.
Still, some homes are not average, so are there cases where a house needs a higher MERV filter?
Absolutely. Some homes should definitely opt for a higher MERV due to special circumstances, but don’t jump up in MERV just to do it.
Read on to see who should raise up their MERV rating and who should not.
Smokers in the Home
Consider this answer an unequivocal “yes.” If you or someone else in your home is a smoker, you need more filtration than a MERV 8 provides.
You already know the devastating effects of cigarettes on the human body, but they aren’t astonishing for air quality either.
An Italian study found that cigarette smoke is worse for air pollution than diesel engines. Cigarettes produce 10 times more damaging air particles than automobile exhaust (source).
Returning to the MERV table from before, you’ll notice filters can capture auto emissions with a MERV of 9 to 12. Meanwhile, tobacco smoke needs a MERV of 13 – 16.
If your home houses a smoker, you should consider a filter with a rating of 13 or more because it can help protect the lungs of the non-smokers who live there.
Houses with Pets
Pets are great! Dogs and cats are our best friends who give us companionship in return for shelter and three meals. With that said, animals are still animals, and they are loaded with potential allergens.
If you have pet allergies and still own a furry friend, you completely understand the effect of invisible pet allergens.
It isn’t just about the fur. Pet allergens come in the form of pet dander as well. Dander is the skin flakes your pet sheds along with fur, and people with pet allergies can’t tolerate the proteins found in the oil gland of animal skin (source).
Salvia is another source, and dogs and cats tend to lick their fur to clean it. When that fur later sheds, you’re left with salvia-laden fur.
Animal salvia is an allergen, but giving up your pal isn’t an option, so now what? The right filter can keep that fur and dander out of your respiratory system. According to the ASHRAE, pet owners should opt for a MERV rating of 10 or higher.
Some pet owners with more severe allergy issues may benefit from a HEPA filter instead of a traditional one.
Pet owners should also change their filters more often than homeowners with no pets. In general, homes with pets are creating more particulates daily than an animal-free home (source).
Those with Chronic Conditions
Certain health conditions can benefit from filters with higher MERV ratings. These conditions include respiratory disorders, such as asthma, chronic obstructive pulmonary disease (COPD), and allergies.
Chronic respiratory diseases (CRDs) are not curable, and household air pollution can aggravate these diseases (source).
If someone in the home is suffering from a respiratory disorder, a higher MERV filter may be what the doctor ordered. A filter with a MERV 13 rating can capture virus carriers, microscopic allergens, and even bacteria.
Studies have shown that proper air filtration can help symptoms of allergy sufferers. According to the American College of Allergy, Asthma, and Immunology (ACAAI), those with respiratory conditions should opt for a MERV rating of 11 to 13.
The ACAAI also notes that a HEPA filter can also help those with chronic issues (source). Air purifiers and humidifiers can also relieve symptoms.
What about Viruses?
The global coronavirus pandemic of 2020 made us all think twice about viruses and air quality. Experts can’t seem to agree if the highly contagious virus is airborne or not.
Still, whether it’s airborne or not, filters can help protect us. Thankfully, all air filters can handle stopping viruses from entering our home’s air, right?
Actually, no. The majority of air filters are not equipped to stop viruses. Only filters with a MERV rating of 13 or higher can capture airborne viruses and bacteria from coughs and sneezes.
Because of this, hospitals and residential inpatient care centers should only utilize air filters with MERV ratings of 13 to 20 (source).
Does this mean you need to rush out and panic-buy all the MERV 13 filters? No. As stated before, anything MERV 8 or higher is adequate for a residential home. The virus causing COVID-19 is probably not lurking in your HVAC system.
What about Peace of Mind?
What if a higher MERV would put your mind at ease? A higher efficiency filter probably won’t cause you any issues, but it could. There are potential downsides, though.
Air filters add resistance to airflow and, for trapping particles, this is ideal. As you travel up the MERV rating scale, you are adding more and more resistance.
Your system is calibrated to work with a certain resistance. If you add more resistance than it can handle, the system will have to use more energy, meaning higher monthly bills.
Too much air resistance will also affect your comfort. Low airflow can mean your system can’t adequately cover your entire home, and suddenly you’ll be left with a cool home but one room that is in near-desert conditions.
The worst-case scenario is that you damage your system. The wrong filter can damage the compressor or crack the heat exchanger (source). Limiting the airflow with too high of a MERV can spell trouble.
The moral here is that you should always check your system’s requirements before upgrading to a different filter.
No Matter What – Replace It
No matter what MERV rating you decide to use in your HVAC system, there is one thing to remember. An air filter will do no good if it’s caked in filth; therefore, you should change your filter every 30 days.
Some manufacturers design air filters to last more prolonged periods so that certain kinds can go up to 6 months without a change.
If you aren’t sure, however, 30 days is the magic number. In 30 days, if you find your filter is still pretty clean, make a note to recheck it in 10 or 15 days.
You may need to swap out your air filter more frequently if any of the following apply to you (source):
- You have more than one pet
- There are young children in the home
- Someone in the home has allergies or asthma
- The unit is run year-round
- You live on a ranch or a farm
- There is current construction near the home
Final Thoughts
Air filters are a vital component in any building’s HVAC system. For a residential HVAC system, homeowners should choose filters with a MERV rating of 8 or higher. Anything below a MERV 8 just won’t filter out enough for quality air.
However, homeowners should also be wary of climbing too high up the MERV rating scale. A high-MERV filter traps more particles, but not all systems are equipped to handle them.
In general, an air filter with a MERV of 8 is enough for the average home. It will filter out common particulates like mold, dust mites, and pollen.
Of course, a filter is only as good as the last time you replaced it. It might be time to check your filter now to ensure the best air quality.
