What MERV Rating Should Your Furnace Filter Be?

What MERV measures

MERV stands for Minimum Efficiency Reporting Value. It comes from ASHRAE Standard 52.2, the lab test for how well air-cleaning devices remove particles of different sizes. The EPA explains that MERV reports a filter's ability to capture particles between 0.3 and 10 microns, and its table runs from MERV 1 to MERV 16. The rating reflects the filter's worst showing across the test. That's where "minimum" comes from.

Higher MERV, better capture of small particles. The EPA's table gives MERV 13 at 50 percent or better for particles of 0.3 to 1 micron, 85 percent or better for 1 to 3 microns, and 90 percent or better for 3 to 10 microns. Smoke lives in that smallest band. Pollen and most dust are bigger and easier to catch.

What the EPA and ASHRAE recommend

They agree, with a catch.

The EPA says to choose a filter rated at least MERV 13, or as high a rating as your system's fan and filter slot can accommodate, and to ask an HVAC technician which is the highest-efficiency filter that'll work for your system.

ASHRAE's filtration guidance calls MERV 13 one good option, not a requirement. It warns that higher efficiency generally brings higher pressure drop, and says to make sure your system can handle an upgrade without hurting airflow before you swap filters.

So aim for MERV 13 if your equipment can take it. Everything below is about that "if".

The airflow trade-off

A denser filter catches more and also fights airflow more. Your blower was sized to push a certain amount of air against a certain amount of resistance from the ductwork, the coil and the filter combined. Pile on too much at the filter and you get one of two outcomes. Less air moves, which can hurt comfort, strain the equipment and cost efficiency. Or a variable-speed blower works harder to keep up.

You have two things on your side. The first is depth. A 4-inch or 5-inch media filter has far more pleated surface than a 1-inch filter with the same face size, so at the same MERV it usually resists airflow less and lasts longer. If your system has a deep filter cabinet, use it.

The second is fit. ASHRAE stresses that filters need to be properly sealed, because air sneaking around the edges of a loose filter doesn't get filtered at all. That undoes the whole upgrade.

Watch for weaker airflow at the registers, a whistle at the filter slot or return grille, or a filter bowing inward. Any of those says the filter's too restrictive. For a definitive answer, a technician can measure static pressure across the filter and compare the system's total to the maximum external static pressure on the furnace's rating plate or in its manual.

MERV vs MPR vs FPR

Store shelves use three different scales. Only one is an industry standard.

• MERV: ASHRAE 52.2, used across the industry.
• MPR (Microparticle Performance Rating) is 3M's scale for Filtrete filters. 3M says it rates capture of particles from 0.3 to 1 micron.
• FPR (Filter Performance Rating) is The Home Depot's scale for the filters it sells, shown as numbers and colors.

3M publishes its own MPR-to-MERV comparison:

No independent standards body publishes an FPR conversion. Look for a stated MERV on the package or product page and compare on that.

How to choose, step by step

1. Measure the slot. Filters are sold by a rounded nominal size, and the real size runs slightly smaller, so match the size printed on the old filter's frame, depth included.
2. Start with what the equipment maker says. Your furnace or air handler manual may list acceptable filter types or a maximum pressure drop.
3. Aim for MERV 13 if the system allows it, especially if someone in the house has allergies or asthma, or you get wildfire smoke.
4. Go deeper before you go denser. A 4-inch MERV 13 usually restricts airflow less than a 1-inch MERV 13.
5. Pay attention for the first few weeks. Check airflow at the registers and listen at the return, and drop down a level if the system struggles.
6. Change it when it's dirty. A loaded filter of any rating chokes airflow, so check it regularly and replace it when it's visibly dirty or at the maker's interval, whichever comes first.

Sources

• EPA: What is a MERV rating? (updated January 2026).
• ASHRAE: Filtration and disinfection guidance.
• 3M Filtrete: MPR vs MERV.

Furnace filter FAQ

What MERV rating should I use in my furnace?

The EPA suggests a filter rated at least MERV 13, or as high as your system's fan and filter slot can handle. ASHRAE calls MERV 13 one good option, not a requirement, and says to upgrade only if your system can take it. Not sure if yours can? A technician can check before you switch.

Is a higher MERV filter bad for my furnace?

Not automatically. It can be. ASHRAE notes that higher filter efficiency generally means more pressure drop across the filter, so the blower works harder to move the same air. On a system with little spare fan capacity or a small filter slot, a dense filter can cut airflow. A deeper filter with more media spreads that resistance out.

What is the difference between MERV, MPR and FPR?

MERV comes from ASHRAE Standard 52.2 and covers particles from 0.3 to 10 microns. MPR is 3M's Filtrete scale, focused on particles from 0.3 to 1 micron. FPR is The Home Depot's in-store scale. Only MERV is an industry test standard, so compare filters by MERV whenever the package lists it.

Is MPR 1500 the same as MERV 13?

Not quite, since the scales measure different things. 3M's own comparison sheet pairs MPR 1500 with MERV 12, and MPR 1900 and MPR 2200 with MERV 13.

How often should I change a furnace filter?

Go by the filter and furnace makers' guidance, and actually look at the filter instead of trusting the calendar. Deeper filters usually last longer than 1-inch ones. Pets, construction dust and smoke all load a filter faster. If it looks gray and clogged, it's choking airflow no matter how old it is.