If you want a quick answer that fits most residential furnaces, then a MERV of 8-10 is it.
But if you’re concerned about indoor air quality (IAQ), allergies or the durability of your HVAC system, then there is more to the issue. A lot more.
Professional MERV Rating Recommendation
What’s the recommended MERV rating for a gas furnace or air handler? It would be easy to say “MERV 8” or “MERV 12” or “the higher the MERV the better.” But none of those statements are true in all circumstances, though they’re the kind of simple answers you get online.
But if you’ve read Pick HVAC articles before, then you know that we don’t give short answers and pretend “one size fits all.” Instead, our HVAC pros give all the relevant details, so that you can make an informed decision specifically tailored to your heating and air conditioning situation.
What MERV Rating is Best?
We recommend MERV 6 to MERV 13 filters usually, but that’s a wide range that definitely does not fit all circumstances. Pick one, and the results could be poor filtration that leaves allergy sufferers without relief or, on the high end of the MERV spectrum, could lead to your HVAC equipment breaking down and needing expensive repairs or replacement.
That’s why we’d rather discuss all factors and give guidance based on your heating and air conditioning equipment, your home and the needs of those living there.
Our Approach
Most sites start with the basics: What is MERV rating? What do 6 MERV filters remove from the air? 8 MERV? 11 or 13 MERV?
But we find that a lot of homeowners ask a simple question, so we’re going to answer it first. Once we’re on the same page, then we can get into details
Why Isn’t the Highest MERV Rating the Best?
We’re going to make this section brief because MERV ratings that are too high is the subject of an entire page of Pick HVAC information found here.
Air filters work by trapping or capturing particles out of the air that is flowing through them. Air…flowing. Airflow. That’s the whole key to air filtration.
The higher the MERV rating, the more and smaller particles are trapped – more and smaller. Air filters achieve higher filtration with material, called “media,” that is more tightly woven or produced to stop those little, even tiny, particles.
The problem with high MERV filters: Sometimes filters with MERV ratings of 11 and above do their job “too good.” They are so good at stopping the pollutants and stuff that causes allergies from getting through, that they restrict airflow.
They make it too hard for the air to get through.
High MERV and Bad Results
The point of this section is to show that putting in a MERV filter that is too restrictive for your HVAC system is a bad idea.
There are two categories of problems – one for the environment in your home, and another for what harm it might cause to your HVAC equipment.
High MERV Can Make Your House Uncomfortable
There are a couple issues to consider here.
Hot and Cold Rooms: The blower has to push heated air in winter and cooled, dehumidified air in summer to the furthest reaches of your home. If airflow is impeded by the air filter, the pressure will drop in the ductwork. This means there won’t be enough air pressure to get the air to those distant rooms, and they might get uncomfortably hot in summer or cool in winter.
Bad Indoor Air Quality (IAQ): This is rare, but in some cases, restricting the airflow too much with a high-MERV filter will not improve IAQ and might make it worse.
The blower might be working its hardest, but if it can’t push air through a restrictive filter, then it also can’t pull dirty air into the system to remove those nasty impurities. They just keep floating around in the air you’re breathing.
Secondly, when dirty air can’t get through the filter fast enough, some of it will find a way around the filter and be pushed into your home without being filtered at all. Dirty air in; dirty air out.
In fact, the pressure on the filter might become so great that a lot of the tiny pollution particles and allergens in it will get forced through the filter and be free to blow into your living space where it makes the air quality worse than it was.
Too-high MERV Can Damage your Equipment
Here’s an overview of the damage that can occur:
Blower Damage: This is an obvious one. When a blower has to work harder to push air through a thicker, denser filter than it is designed for, it can wear out faster or simply burn out all at once. Older and budget furnaces typically have motors called PSC motors – and they are far more susceptible to ECM motors found in newer and better furnaces.
Cracked Furnace Heat Exchanger: Your furnace creates a lot of heat. If that heat can’t get distributed through ductwork because of a restrictive filter, the inside of the furnace might overheat. The worst possible scenario is that the heat exchanger will overheat and crack. When that happens, furnace replacement is the most common result. And if it runs with a cracked heat exchanger, deadly carbon monoxide gas could escape into the air you breathe.
AC or Heat Pump Compressor Damage: When not enough treated (heated or cooled) air gets circulated to make the thermostat happy, it keeps the compressor working to cycle refrigerant through the system. The compressor can wear out or fail too, and if it does, an entire new outside unit is often required.
Is it Dirt or Direction? A high-MERV filter isn’t the only cause of these issues. Climate control and mechanical trouble can both be caused by a filter installed in the wrong direction and by a dirty filter. Learn about Furnace Filter Direction in this guide and about dirty filters in How to Tell If I Should Change a Filter.
What About Energy Costs?
On top of indoor discomfort and potential mechanical issues, a system that works too hard will use more energy, and your utility costs will go up. ECM blower motors don’t burn out as much with restrictive airflow – they just burn more energy.
MERV Ratings – What to Consider
As we said at the top, most HVAC air handlers and furnaces work best with a MERV 8 or MERV 10 filter, and filters with that level of filtration will do an adequate job in most homes if there are no extenuating circumstances. What types of circumstances could require a higher-MERV filter? Medical issues among household members, an exceptionally dusty or polluted environment or a need for higher-than-average filtration because sensitive equipment is in the home.
There are three considerations here.
First, what do MERV filters at each numeric level or tier remove from the air?
Secondly, is the highest MERV rating your equipment is designed to handle?
Thirdly, can your system be modified to handle a filter with a higher MERV rating? The answer to this question is, “Yes,” and it is discussed below.
See our What is MERV Guide if you want more on MERV basics and applications.
MERV Ratings – What Can Filters Remove?
MERV stands for “minimum efficiency reporting value,” a phrase which means very little to non-professionals. But the idea is obvious – the higher the MERV rating, the more and smaller particles the filter removes.
For example, a MERV 6 filter will trap about 50% of pollen but only about 25% of mold spores. A MERV 10 filter will trap more than 85% of pollen and about 75% of mold spores.
This chart is an overview of MERV Ratings and what pollutants each tier removes. The higher the MERV for each set, like MERV 8-10, the more of the pollutant will be removed. A MERV 8 filter removes about 70% of pollen while a MERV 10 removes 85% of pollen.
| MERV | .3 to 1.0 Microns | 1.0 to 3.0 Microns | 3 to 10 Microns | Best For: (1) |
|---|---|---|---|---|
| 1 – 4 | Less than 20% | Less than 20% | Less than 20% | Large pollen, hair, carpet fiber |
| 5 – 7 | Less than 20% | Less than 20% | 20% to 65% | Mold spores, dust mites |
| 8 – 10 | Less than 20% | 20% to 65% | 70% to more than 85% | Dust, dust mite debris, smoke, pet dander |
| 11 – 13 | 20% to 70% | 65% to more than 90% | 85% to more than 90% | Bacteria, sneeze droplets, auto exhaust |
| 14 – 16 | 75% to more than 95% | 90% to more than 95% | 90% or more | Odors, large viruses, fungi, VOCs |
Each level will remove all the pollutants listed above it plus those listed in that tier.
MERV 1 – 4
We do not recommend filters in this tier. They are cheap spun fiberglass filters mostly, and MERV 1-4 air filters do a poor job removing anything but the largest particles that could damage your furnace or cause bad air.
- Particle size and pollutants: These filters can be relied upon to remove particles of 10 microns and larger including large pollen, human and pet hair, carpet fibers and lint. They might stop dust mites too, but not their droppings, which are far worse allergens.
- Thickness: 1-inch filters are your only option.
- Replacement: Every 1-2 months when the system is in operation.
MERV 5 – 7
These are better-quality furnace filters that are the best-sellers because they’re pleated, so they look like they do a better job. But they’re still inexpensive at $8-$15 per filter.
- Particle size and pollutants: Expect filters in this range to do a pretty good job on particles from 3 to 10 microns. These include pollen, dust mites, dust and mold spores.
- Thickness: Most are pleated 1-inch filters, but you can find 2-inch filters in the MERV 5-7 range too.
- Replacement: Every 1-3 months depending on how heavily you run the HVAC system and how dusty your environment is.
MERV 8 – 10
We recommend filters in this range for most homes.
Their effectiveness in removing the most common pollutants and allergens makes them a good choice for anyone who does not have breathing issues or has mild asthma or allergy symptoms.
- Particle size and pollutants: MERV 8-10 air filters remove a high percentage of particles 3 to 10 microns and most of those 1-3 microns. These include dust, dust mite debris, cooking smoke, pet dander and large bacteria like legionella.
- Thickness: These pleated filters come in 1, 2 and 4-inch sizes. The importance of the ratio of thickness to MERV is explained below when discussing how to increase filtration without harming your HVAC equipment.
- Replacement: 1-12 months. Thicker filters of the same MERV rating as a 1-inch filter don’t need to be changed as often.
MERV 11 – 13
This is the tier we recommend for homes where someone has severe allergies, asthma or other lung/breathing ailment.
- Particle size and pollutants: These remove most particles of 1-3 microns and many that are smaller than 1 micron. Use a MERV 11-13 filter to remove all the pollutants already mentioned plus smaller bacteria, auto emissions, very fine dust and
- Thickness: 1, 2 and 4 inches.
- Replacement: 1-2 months for 1”, 2-4 months of 2” and up to 8 or 9 months for 4” filters.
MERV 14 – 16+
Filters with this level of filtration efficiency should be used with caution. We don’t recommend them unless your furnace or air handler has a blower rated for them – and most don’t.
- Particle size and pollutants: MERV 14, 15 and 16 filters remove a high percentage of particles down to .3 microns. These include VOCs, fungi, large viruses and most odor-causing agents such as paint fumes.
- Thickness: 1 to 6 inches
- Replacement: The same schedule as for MERV 11-13 filters. Because these filters are very restrictive to airflow, it is essential that you change them before they get extremely dirty. Running equipment on a very dirty, very restrictive filter is the most common cause of damaged HVAC equipment.
How Big are Air Pollutants?
They vary within each category, but here are size ranges for common forms of indoor pollution and allergens.
- Lint: 3 to 10+ microns
- Hair: 1-3 microns
- Dust: 1 to 10 microns
- Dust Mites: More than 10 microns
- Pollen: More than 10 microns
- Dust Mite Debris: 5 to 10 microns
- Mold Spores: 2 to 15 microns
- Pet Dander: .3 to 10 microns
- Smoke/Smog: .005 to .05 microns
- Sneeze Droplets: .3 to 2 microns
- Auto Emissions: .3 to .8 microns
- Bacteria: .3 to 4 microns
- Viruses: Less than .3 to .5 microns
- VOCs: Less than .3 to .5 microns
- Odors: Less than .3 to .8 microns
Common Home Pollutants and Allergens
Do you know what kinds of pollutants are found in your home?
All Homes: All homes have dust, much of which is flaked-off human skin. If you cook, especially fry, then you might have some cooking smoke and odors. Most homes also have some dust mites and their waste, or debris. The amounts of bacteria vary quite a bit from home to home based on how much attention is given to cleaning and whether pets are indoor-only or whether they come in and out of the house.
Most Homes: The majority of houses also have some VOCs, or organic volatile compounds. They are found in many household items especially flooring, upholstery, cleaners, dry-cleaned clothes, heavily scented soaps/candles/detergents, perfume, paint and nail polish.
However, if you’re aware of VOCs and make a commitment to buy low-VOC or non-VOC products, then you might not have a lot of them. Manufacturers make low-VOC flooring and other building materials, cleaners and other household products, but you have to be intentional about buying them.
Fewer Homes: There are other pollutants that fewer homes have – cigarette smoke, auto emissions from an attached garage and spray pesticides are among less common concerns.
Recommended MERV Rating
Perhaps it is clear by now that we recommend filters in three tiers:
MERV 5-7 These filters are a good fit when:
- Health: No household member or pet has breathing trouble or allergies
- Cleaning: The house is dusted, vacuumed and cleaned weekly
- Flooring: Most flooring is hard – since carpet is the biggest collector of dust and other allergens, and they get stirred into the air when the carpet is walked on
- Pets: There are no pets that shed heavily
- Environment: Levels of dust, pollen or industrial pollution in your area are low to average
- Budget: Lower cost for filters is a high priority
MERV 8-10 These filters make sense for most homes including when:
- Health: One or more household members have mild allergies or asthma
- Cleaning: Sometimes vacuuming and dusting get overlooked for a few weeks
- Flooring: Several rooms at least have carpet on the floors instead of hard flooring like laminate, wood or tile
- Pets: There are up to 2 pets that shed significant amounts of fur/hair
- Budget: Moderate filter cost – up to $25 per filter – is OK
- Environment: Your area has some industrial pollution, heavier-than-average pollen because of farm fields, woods or meadows nearby or the area around the house is dry and dusty
MERV 11-13 These filters are acceptable when several of these factors are present:
- Health: One or more household members have severe allergies, asthma, C.O.P.D. or other breathing trouble
- Cleaning: Dusting and vacuuming are overlooked some weeks, and dust and debris sometimes build up
- Flooring: Most flooring is carpet or large area rugs are used
- Pets: There are up to 4 shedding pets in the household
- Budget: Paying around $25-$50 for an air filter is fine
- Environment: There is a significant amount of pollution, pollen and/or dust in your immediate area
MERV 14-16 These filters can be used when the blower can handle the restriction in airflow. They are mostly used in residential settings when:
- Health: Several household members have severe allergies, asthma, C.O.P.D. or other breathing trouble
- Cleaning: Dusting and vacuuming are overlooked some weeks, and dust and debris sometimes build up
- Flooring: Most flooring is carpet or large area rugs are used
- Pets: There are up to 4 shedding pets in the household
- Budget: Paying up to about $100 per filter is OK
- Environment: There is severe pollution, pollen and/or dust in your immediate area and/or you need superior filtration to protect sensitive electronic equipment
Higher MERV Without Problems
HVAC equipment manufacturer Rheem says, “Most furnaces [and air handlers] work best with a filter rated between 8 and 11. Check with your furnace manufacturer to determine if your model has a recommended maximum MERV rating.
Pick HVAC agrees with both those statements – MERV 8 to 11 are the best ratings for most furnaces and air handlers. The blower likely won’t wear out “before its time” when using them. Sure, MERV 11 might be pushing it a bit, but you should be OK if you change the filter before it gets heavily clogged.
Secondly, it is important to know what the manufacturer of your furnace or air handler says about max MERV. The information might be found in your owner’s manual, which can be located online if you don’t have it but do have the furnace/air handler make and model number.
Tips for higher MERV without problems:
- Don’t exceed the manufacturer’s recommendation.
- Use a thicker filter of the MERV you want. For example, most 1-inch MERV filters with a 13 rating are denser and restrict airflow a lot more than 2-inch and 4-inch MERV 13 filters. You might need to have your system modified to accommodate a thicker filter, but the $300 to $600 it will cost is a good investment compared with having to replace the blower, entire furnace or the outside unit because the compressor burns out.
- Consider also using an air purifier with a True-HEPA filter. True-HEPA filters are equivalent to MERV 17 to 20, so if your air filter can’t remove all the smallest particles from the air in your home, then the air purifier will definitely improve indoor air quality. The Pick HVAC Guide to the Best Air Purifiers for Dust is a good place to locate an effective and affordable HEPA air purifier for your home.
What are MPR and FPR Ratings?
They are ratings similar to MERV but designed by manufacturers 3M and Honeywell. Here’s a fuller explanation.
