MERV ratings
What MERV rating do I need?
For most homes, MERV 8. Pick MERV 11 for pets or allergies and MERV 13 for wildfire smoke, if your system can move air through it. A deeper 4-inch or 5-inch filter handles high ratings more easily than a 1-inch one.
What MERV measures
MERV (Minimum Efficiency Reporting Value) comes from a lab test that counts how much of each particle size a filter stops. The scale runs from 1 to 16 for home and commercial filters. Higher catches smaller particles, and also pushes back harder on the air.
The four ratings you will see
| Rating | What it catches | Choose it if |
|---|---|---|
| MERV 6 | Lint, larger dust and some pollen. At least 35% of particles from 3 to 10 microns. | You want basic protection for the furnace and the cheapest pleated filter. |
| MERV 8 | Dust, pollen, mold spores and lint. At least 70% of particles from 3 to 10 microns. | You want a good default. Works in almost every system. |
| MERV 11 | Adds pet dander and finer dust. At least 65% of particles from 1 to 3 microns. | You have pets or seasonal allergies. |
| MERV 13 | Adds smoke and very fine particles. At least 50% of particles from 0.3 to 1 micron. | Wildfire smoke reaches you, someone has asthma, or your HVAC company recommends it. |
Percentages are the minimums in the ASHRAE 52.2 test for each rating.
When a higher MERV is too much
A denser filter makes the blower work harder to pull air through. In a thin 1-inch slot on an older furnace, a MERV 13 filter can cut airflow enough to make rooms uneven, the coil colder, or the furnace run hotter than it should.
Signs to watch for after a switch: weaker air at the registers, a louder whoosh at the return, or the filter bowing into the slot. If you see them, step back down a rating or ask your HVAC company about a deeper filter cabinet.
Depth matters as much as the number
A 4-inch or 5-inch media filter has several times the pleated area of a 1-inch filter, so it can carry MERV 11 to 13 with less resistance and last 6 to 12 months.
MERV questions
Is a higher MERV rating always better?
No. Higher ratings catch smaller particles but restrict more air. MERV 8 is the safe default; go to 11 or 13 only if your system can handle it, which is easier with a 4-inch or 5-inch filter.
What MERV rating is best for pets?
MERV 11 catches most pet dander. Change it more often than you would without pets, since hair clogs it sooner.
What MERV rating helps with wildfire smoke?
MERV 13 or the highest your system can handle. Run the furnace fan during smoky days so air passes through the filter, and check the filter after a smoky week.
Can a MERV 13 filter damage my furnace?
It can strain an older furnace with a small 1-inch slot by cutting airflow. Watch for weak airflow or a bowing filter after the switch, and ask your HVAC company if you are unsure.
What is the difference between MERV and MPR or FPR?
MERV is the industry test. MPR (Filtrete) and FPR (Home Depot) are store brand scales. Compare them through the MERV number printed on the package when it is there.
Does a higher MERV filter need changing more often?
Usually yes, because it fills faster. Check a high MERV 1-inch filter monthly until you know how quickly it loads.