How Furnace Filters Are Rated

When it’s cold outside, our indoor heating furnace keeps us comfortable inside. Your furnace filter plays an important role in your furnace system and should be changed monthly. Otherwise, your filter can become clogged and lead to several major problems that may go beyond simple furnace maintenance.

The furnace filter protects major furnace components. The filter prevents the heat exchanger from overheating. It protects the blower fan from the dust, hair, dander, and other air pollutants that the duct sucks into the furnace system. While your filter also cleans the air, the point of the furnace filter is to stop debris from damaging the system.

When shopping for furnace filters, you may have realized that there are many different ratings and sizes. Some filters are electric, disposable, and even washable. While your furnace system should tell you what size and type are necessary, choosing what rating can be intimidating if you don’t know what you’re looking for.

Continue reading to discover more about the rating process for furnace filters.

MERV System

Furnace filters are rated by their efficiency. The industry uses a measurement system called the Minimum Efficiency Reporting Value (MERV). The American Society of Heating, Refrigeration and Air Conditioner Engineers (ASHARE) created MERV. Essentially, the MERV system measures the minimum level that the filter will remove particulates as small as .3 to 10 microns (micrometers). Microns/micrometers are a millionth of a meter which is really small. These particulates can include dust, smoke, pet dander, mold spores, and more.

MERV measures the efficiency of your filter on a scale of 1 to 16. Higher ratings mean that the filter will remove more particulate matter from the airflow. This will keep all the particulates from reaching the blower fan, motor, and heat exchanger and causing costly damage.

But that doesn’t mean that you need the highest rated MERV. Higher rated filters block more air from flowing through. This may lead to your furnace system overworking and driving up your utility bills. Additionally, an overworked furnace system is more likely to malfunction. You should check if your furnace model has a maximum MERV rating. As MERV ratings climb, so do the prices. Since very high MERV rated filters tend to be more expensive, they’re usually only a good investment in special cases.

The following chart shows what particles are removed with each MERV rating:

MERV Rating Particulates
1-4 Pollen, bugs, dust mites, sanding dust, paint debris, textile and carpet fibres
5-8 Dust mibe debris, pet dander, mold spores, hair spray, pudding mix, aeorsol sprays
9-12 Humidifier dust, legionella (pneumonia-causing bacteria), lead dust, flour, auto emissions
13-16 Bacteria, sneeze droplets, cooking oil, cooking aerosols, smoke, makeup powder, paint pigments, insecticide dust

Most home furnaces and commercial workspaces use a 7 and 12 on the MERV system. This will remove most particulates from the air without restricting airflow to the furnace.

When should I use a high MERV rating?

As we mentioned, you should only use a high rated MERV filter in certain cases, as they can lead to higher utility bills and furnace malfunctions. However, high-rated furnace filters do have a time and place, especially because they do an excellent job of cleaning the air. These situations include:

  • Homes with residents who suffer from severe allergies
  • Homes with residents who have asthma
  • Hospitals, medical facilities, or doctors’ offices. MERV ratings of 13-16 are known as “hospital-level air quality.”

Other Rating Systems

Some home improvement stores like Home Depot use their own system so you should check for conversions.


Home Depot uses a system called Air Filter Performance Rating, or “FPR.” Instead of being ranked on a scale of 1-16 like MERV, FPR rates filters on a scale of 1-10, with ten being the highest performance. There are three key measurements that make up an FPR score. These include:

  • Ability to capture large particles. This accounts for 60% of a filter’s score.
  • Ability to capture small particles. This accounts for 30% of a filter’s score.
  • Weight gain caused by capturing particulates over the filter’s lifetime. This accounts for the final 10% of its score.

Since MERV measures based on minimum efficiency on a scale of 1-16 and FPR measures three different degrees of performance on a scale of 1-10, a 5 on the MERV scale will not equal a 5 on the FPR scale. The following chart demonstrates which particulate are removed with each FPR rating:

FPR Rating Particulates Removed
FPR 4-5 – Good Dust mites, dust, lint, pollen, pet dander
FPR 6-7 – Better Dust mites, dust, lint, pollen, pet dander, bacteria, and mold spores
FPR 8-9 – Best Dust mites, dust, lint, pollen, pet dander, bacteria, mold spores, smoke, allergens, virus-carrying particulates
FPR 10 – Premium Dust mites, dust, lint, pollen, pet dander, bacteria, mold spores, smoke, allergens, virus-carrying particulates, odor-carrying particulates

J.A. Bertsch

Gear up for the long Idaho winter with heating installation, repair, and maintenance services from J. A. Bertsch Heating & Cooling.  We proudly service all makes and models of heaters, and we stock an assortment of the best brands available should you require a full-system replacement. For the most trusted heating furnace repair services in North Idaho call the professionals at 208-715-9694.

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