The short answer: the EPA says that if you're upgrading your HVAC filter, choose at least MERV 13, or the highest rating your system's fan and filter slot can handle. It also says most home furnaces and HVAC systems can take a MERV 13 filter without equipment problems, as long as you change it often. If you're not sure about yours, ask an HVAC technician.
Once you've picked a rating, the next question is timing. Our guide to how often to change your HVAC filter covers that, and the how often to replace lookup lists every filter in the house in one place.
What MERV measures
MERV stands for Minimum Efficiency Reporting Value. It comes from a test method developed by ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers), and it shows how well a filter catches particles between 0.3 and 10 microns (EPA). The scale runs from 1 to 16, and a higher number means the filter traps a bigger share of each particle size.
HEPA filters sit outside the scale. The EPA lists them separately, as catching at least 99.97% of particles at 0.3 microns.
MERV 8 vs 11 vs 13
These are the minimum shares each rating must catch in the test, in three particle size ranges (EPA).
| Rating | Smallest (0.3 to 1 micron) | Medium (1 to 3 microns) | Largest (3 to 10 microns) |
|---|---|---|---|
| MERV 8 | No minimum | At least 20% | At least 70% |
| MERV 11 | At least 20% | At least 65% | At least 85% |
| MERV 13 | At least 50% | At least 85% | At least 90% |
All three do a fair job on the larger particles. The real difference is the smallest size range: MERV 8 has no minimum there, MERV 11 must catch at least a fifth, and MERV 13 at least half. The EPA notes that filters rated MERV 13 and above have to show at least 50% removal for the smallest particles tested.
Will MERV 13 strain my system?
For most homes, the EPA says no, as long as the filter is replaced often. To be sure about yours:
- Check your furnace or air handler manual for a recommended or maximum filter rating.
- Make sure the filter fits snugly, so air can't leak around the edges, and that you don't have to bend or crush it to get it in (EPA).
- Look at the filter every month. Energy Star says to inspect, clean or change it monthly, and the EPA says to change it more often if it's heavily soiled when you take it out.
- If your system is older or has had airflow problems, ask an HVAC technician. The EPA notes a technician can also modify a system to use a higher-efficiency filter.
Filters come in thicknesses from 1 to 5 inches (EPA). Buy the size your slot is built for.
MERV, MPR and FPR
MERV is based on a national consensus standard. MPR and FPR are proprietary rating scales you'll see on some brands' and stores' packaging (EPA). With every one of these methods, a higher number means better removal for most particle sizes, but the numbers aren't on the same scale, so don't read an MPR or FPR number as a MERV. If the box doesn't show a MERV, look in the product details or ask the maker.
Pets, allergies and wildfire smoke
- Pets and allergies. The EPA doesn't give a separate rating for these. Its advice stays the same: MERV 13, or the highest your system can handle. Check the filter monthly and change it when it looks dirty, which may be sooner in a home with pets.
- Wildfire smoke. The EPA says upgrading to MERV 13 or higher can be especially important during smoky periods, to help remove fine particles. If your system has a fresh-air intake, it suggests closing it while it's smoky. A portable air cleaner with a HEPA filter, sized for the room, adds more protection where you spend your time.
- Run time. A furnace or HVAC filter only cleans the air while the system is running. The EPA says systems usually run less than 25% of the time during heating and cooling seasons, and running the fan longer raises electricity costs.
MERV chooser (printable)
| Rating | What it catches (EPA minimums) | Who it suits | What to check |
|---|---|---|---|
| MERV 8 | 70% of large, 20% of medium, no minimum for the smallest | Systems whose manual or technician says not to go higher | Change it on schedule |
| MERV 11 | 85% of large, 65% of medium, 20% of the smallest | A step up when MERV 13 isn't an option | Snug fit; your manual's maximum rating |
| MERV 13 | 90% of large, 85% of medium, 50% of the smallest | The EPA's pick for most homes, and for smoky periods | Your manual's maximum rating; snug fit; change it often |
| MERV 14 to 16 | At least 75% to 95% of the smallest | Systems built or modified for them | Ask an HVAC technician first |
While you're at the air handler, look at the drain too. Our guide to cleaning the AC condensate drain line shows how.
Questions people ask
Is MERV 13 too high for a home?
Usually not. The EPA says most furnaces and HVAC systems can take a MERV 13 filter without equipment problems if it's changed often. If you're unsure about yours, check the manual or ask an HVAC technician.
MERV 8 or 11?
MERV 11 catches more small particles than MERV 8, including at least 20% of the smallest size range, where MERV 8 has no minimum (EPA). If your system can handle it, the EPA suggests going up to MERV 13.
What does MERV stand for?
Minimum Efficiency Reporting Value. It comes from an ASHRAE test method and shows how well a filter catches particles from 0.3 to 10 microns (EPA).
Does a higher MERV mean changing it more often?
Follow the filter maker's schedule; the EPA says manufacturers typically recommend every 60 to 90 days. If a filter looks heavily soiled when you change it, change it more often.
What's MPR vs MERV?
MERV is based on a national consensus standard. MPR and FPR are proprietary scales used by some brands and stores, so compare filters by their MERV number where you can (EPA).
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Sources
- EPA: What is a MERV rating?
- EPA: Guide to Air Cleaners in the Home
- EPA Wildfire Smoke Course: Preparing for Fire Season
- Energy Star: Maintenance Checklist
General guidance only. Follow your manufacturer's instructions, and call a licensed professional for gas, electrical, roofing or anything that feels unsafe.