Pick MERV 11 if your system can accommodate it and you want a rated capture figure for 0.30 to 1.0 micron particles, the one band where EPA's table gives MERV 8 no figure at all. At The Indoor Report, our rule is to read the MERV number stated on the package, since brand labels such as 'allergen' or 'performance' scales are not the MERV scale.
MERV (Minimum Efficiency Reporting Value) is the scale that the U.S. Environmental Protection Agency (EPA) uses to describe how well an air filter captures particles between 0.3 and 10 microns. EPA says the scale is helpful for comparing filters, particularly for furnace or central heating, ventilation, and air conditioning (HVAC) systems.
EPA says the higher the MERV rating, the better the filter is at trapping specific sizes of particles. EPA says to choose as high a rating as the system fan and filter slot can accommodate. EPA also says filters cannot remove all pollutants, and that filtration supplements source control and ventilation.
EPA's Table Gives MERV 8 No Figure Below 1.0 Micron
EPA's MERV table gives MERV 8 no efficiency figure for 0.30 to 1.0 micron (µm) particles. The first MERV level on that table with a figure in that band is MERV 11, which the table lists at a floor of 20 percent.
EPA states the MERV 8 and MERV 11 figures with the words 'at least,' so each listed number is the minimum EPA reports.
MERV 8 still has EPA figures for the 1.0 to 3.0 and 3.0 to 10.0 micron bands.
EPA says the rating comes from a test method developed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). Pick MERV 8 when your system takes only that rating. Pick MERV 11 when your system takes it and you want a rated figure for the smallest band.
MERV 8 Efficiency by Particle Size, per EPA's Table
EPA's table gives MERV 8 an average capture efficiency of at least 20 percent for 1.0 to 3.0 micron particles. The same table gives MERV 8 at least 70 percent for 3.0 to 10.0 micron particles.
EPA's table gives MERV 7 at least 50 percent in that same band, so MERV 8's 70 percent floor sits 20 percentage points above it.
The 1.0 to 3.0 micron figure is 20 percent, which is the lowest figure EPA lists for MERV 8. A buyer reading that number should treat it as a floor for the middle band, not a high mark.
Reading a MERV 8 entry means the filter has a documented floor for the two larger bands and no published figure for the smallest one. A buyer comparing two packages should look first at the band where one entry is blank.
Each band is named by particle size, not by pollutant. EPA's table names particle-size bands, not pollutants, so it cannot say how MERV 8 handles any one of them.
MERV 11 Adds a Rated 0.30 to 1.0 Micron Band
EPA's table gives MERV 11 at least 20 percent for 0.30 to 1.0 micron particles, at least 65 percent for 1.0 to 3.0 micron particles, and at least 85 percent for 3.0 to 10.0 micron particles.
The 0.30 to 1.0 micron band is the real difference between the two ratings.
Measured against MERV 8's listed figures, MERV 11's floor is 45 percentage points higher in the 1.0 to 3.0 micron band (65 minus 20). In the 3.0 to 10.0 micron band, the difference is 15 points (85 minus 70).
EPA's table lists HEPA filters separately. EPA says high-efficiency particulate air (HEPA) filters capture at least 99.97 percent of 0.30 micron particles, and that HEPA figures are not based on the MERV rating system. For that category, see the HEPA air purifier guide.
The MERV Rating Leaves Out Fan Limits and Replacement Timing
The MERV number describes capture figures for the filter. It does not describe the rating your system can run, and EPA ties that limit to the fan and filter slot.
Filter size is a separate decision from MERV, and the HVAC filter sizes guide covers that measurement step.
EPA says all filters require periodic replacement to function properly, so follow the manufacturer's recommendations.
EPA says furnace and HVAC filters clean the air only while the system operates. In most cases, an HVAC system runs only when heating or cooling is needed, usually less than 25 percent of the time during the heating and cooling seasons. EPA says longer run times increase electricity costs and may result in less reliable humidity control during the cooling season, per EPA's guide to air cleaners.
Retail packaging can use its own scale, such as a vendor's 'allergen' or 'performance' label. Those labels are not the MERV scale, so the MERV number stated on the package is the figure to read.
Both Ratings Sit Below EPA's MERV 13 Advice on Every Listed Band
EPA says that if you upgrade to a higher efficiency filter, you should choose at least MERV 13, or as high a rating as your system fan and filter slot can accommodate.
EPA's table gives MERV 13 at least 50 percent for 0.30 to 1.0 micron particles, at least 85 percent for 1.0 to 3.0 micron particles, and at least 90 percent for 3.0 to 10.0 micron particles. Both MERV 8 and MERV 11 fall below those floors in every band where they have a figure.
MERV 11 falls 30 points short of MERV 13 in the 0.30 to 1.0 micron band (50 minus 20). It falls 20 points short in the 1.0 to 3.0 micron band (85 minus 65) and 5 points short in the 3.0 to 10.0 micron band (90 minus 85).
Staying at MERV 8 or MERV 11 is a system-driven choice.
If your system can take MERV 13, the MERV 13 filter guide covers that next step up.
Specifications at a Glance: MERV 8 Compared With MERV 11
This table lists each MERV 8 and MERV 11 figure from EPA's table, with the test method source and the fit consideration EPA gives for both.
| Dimension | MERV 8 | MERV 11 |
|---|---|---|
| 0.30 to 1.0 µm efficiency | Not listed by EPA | At least 20%, per EPA's MERV table |
| 1.0 to 3.0 µm efficiency | At least 20%, per EPA's MERV table | At least 65%, per EPA's MERV table |
| 3.0 to 10.0 µm efficiency | At least 70%, per EPA's MERV table | At least 85%, per EPA's MERV table |
| Test method and source | ASHRAE test method, as described by EPA | ASHRAE test method, as described by EPA |
| Fit consideration | Set by the fan and filter slot, per EPA | Set by the fan and filter slot, per EPA |
Which Furnace Filter Rating to Choose
Choose MERV 11 when your system's fan and filter slot accept it and you want a rated figure for the 0.30 to 1.0 micron band, which EPA's table does not give MERV 8. Choose MERV 8 when your system takes only that rating, because EPA says the highest rating depends on the fan and filter slot.
EPA advises at least MERV 13 where the system can take it, so this comparison does not serve a household whose system can take MERV 13. It also does not serve a reader who wants a named pollutant removed, because EPA's table lists particle-size bands and not pollutants.
A change in the fan or filter slot would change the answer. EPA also says a professional HVAC technician can determine the highest efficiency filter that works for a given system, and that advice would change the pick. Next, read the MERV number on the package and measure the filter slot with the HVAC filter sizes guide.
Common questions
Is MERV 11 better than MERV 8?
Yes, on EPA's table, in each band where both ratings have a figure. MERV 11 lists a higher floor in each band where both ratings have a figure, and it adds a figure for 0.30 to 1.0 micron particles that MERV 8 does not have. Which one fits still depends on the fan and filter slot.
Is a higher MERV always better?
No. EPA says to choose as high a rating as the system fan and filter slot can accommodate. EPA's guidance sets the ceiling at what the system can take.
Does a MERV 11 filter catch pet dander, dust, or smoke?
EPA's table lists particle-size bands, not named pollutants, so the table does not state how a MERV 11 filter handles pet dander, dust, or smoke. EPA also says filters cannot remove all pollutants, and that filtration supplements source control and ventilation.
How often should I change a MERV 8 or MERV 11 filter?
Follow the manufacturer's recommendations. EPA says all filters require periodic replacement to function properly.
Do I need an air purifier if I already have a MERV 11 furnace filter?
EPA says central furnace or HVAC filters filter air throughout a home, and that filtration supplements source control and ventilation. A furnace filter does not replace the other steps. For a side-by-side look at the two categories, read the air purifier vs air filter guide.
What drives the cost difference between MERV 8 and MERV 11 filters?
No dollar figure is given for either rating. The input EPA does publish is how long the system runs, which EPA puts at usually less than 25 percent of heating and cooling season time. EPA says longer run times increase electricity costs.