What MERV ratings mean and which furnace filter to choose

If you are choosing a furnace or HVAC filter, the MERV rating tells you how well it captures small particles. This guide covers what the rating means, EPA's figures for MERV 8, 11, 13 and 16 filters, and when a MERV 13 filter makes sense. It also covers how MERV compares with FPR and MPR, and how often EPA and ENERGY STAR say to change a filter.

What a MERV rating measures

EPA's MERV page says, "Minimum Efficiency Reporting Values, or MERVs, report an air filter's ability to capture particles between 0.3 and 10 microns (µm)." The rating comes from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). EPA adds, "The higher the MERV rating, the better the filter is at trapping specific sizes of particles."

EPA's July 2018 technical summary on residential air cleaners, an older EPA source, names the test. It is ASHRAE Standard 52.2, which EPA calls "a national consensus standard." Results are reported as MERV 1 to MERV 16, based on the average removal across three particle size ranges: 0.3 to 1 µm, 1 to 3 µm, and 3 to 10 µm.

MERV 8, 11, 13 and 16 compared

EPA's table lists the minimum average capture for each rating. Every figure is "greater than or equal to" the number shown.

MERV	0.3 to 1.0 µm	1.0 to 3.0 µm	3.0 to 10.0 µm
8	Not listed	20% or more	70% or more
11	20% or more	65% or more	85% or more
13	50% or more	85% or more	90% or more
16	95% or more	95% or more	95% or more

The same EPA page lists figures for HEPA filters. EPA notes that those HEPA figures "are not based on the MERV rating system," so a MERV number and a HEPA rating are not on the same scale.

Should you use a MERV 13 filter?

EPA's Guide to Air Cleaners in the Home, last updated October 1, 2026, gives direct advice. "If you decide to upgrade or use a higher efficiency filter, choose a filter with at least a Minimum Efficiency Reporting Value (MERV) 13 rating, or as high a rating as your system fan and filter slot can accommodate." It adds that you may need an HVAC technician to find the best filter for your system.

The guide also says, "Filters with a MERV of 13 and above are required to demonstrate at least 50% removal efficiency for the smallest particles tested." It adds that "most furnaces and HVAC systems can accommodate a MERV 13 filter without creating equipment problems, provided that the filter is replaced frequently."

A filter only cleans air that passes through it. EPA says furnace and HVAC filters work "only when the system is operating." In most cases, systems run only when heating or cooling is needed, which EPA says is "usually less than 25% of the time during heating and cooling seasons."

MERV 13 filters and airflow

A higher-efficiency filter can make it harder for air to move through the system. EPA's 2018 technical summary says choosing any higher-efficiency filter, "including MERV 13 to 16 or HEPA," must take into account whether it is compatible with the existing ducted system. The goal is "to ensure that airflow will not be impeded by the added resistance of the filter."

It is not always easy to know what your system can take. EPA's guide says HVAC systems "are not commonly labeled with any filter recommendations." It suggests asking a professional HVAC technician, who can find the most efficient filter your system can use. A technician can also modify the system to use a higher efficiency filter.

Fit matters too. EPA says filters commonly come in thicknesses of 1 to 5 inches. It says to make sure the filter "fits snugly so air does not leak around the filter" and that you do not have to bend or crush it to make it fit.

We found no government source in this research that puts a number on how much a MERV 13 filter changes airflow or energy use.

MERV vs FPR and MPR

You may see other ratings on filter packages. EPA says common filter rating methods include MERV, Filter Performance Rating (FPR) and Microparticle Performance Rating (MPR). "MERV is based on a national consensus standard. The FPR and MPR rating methods are proprietary." We found no EPA conversion between MERV and FPR or MPR, so this guide does not offer one.

How often to change a furnace filter

EPA and ENERGY STAR word their advice differently.

Source	What it says
EPA, Guide to Air Cleaners in the Home	Replace filters according to the manufacturer's recommendations. Manufacturers typically recommend every 60 to 90 days. If filters look heavily soiled when you replace them, consider changing them more often.
ENERGY STAR, Heat & Cool Efficiently	Check the filter every month, especially in winter and summer. If it looks dirty after a month, change it. At a minimum, change it every 3 months.

Both pages say a dirty filter should be changed sooner. If you use your system heavily, check the filter more often.

Limits of HVAC filters and window units

EPA says most window air conditioners and wall-mounted units "are intended for temperature control rather than air filtration." Their filters are mostly meant to keep the inside of the unit clean, not to remove fine particles from indoor air.

EPA also warns, "Avoid portable air cleaners and furnace/HVAC filters that intentionally produce ozone. Ozone is a lung irritant."

EPA treats filtration as a supplement to other steps. On its air cleaners and filters page, EPA says the most effective ways to improve indoor air are to reduce or remove pollutant sources and to ventilate with clean outdoor air. It adds that "filtration can be an effective supplement to source control and ventilation."

For filter advice during smoke events, see our guide to protecting your home from wildfire smoke. For furnace and central air upkeep, see our guides to furnaces and central air conditioning.