MERV 8 vs MERV 13
Quick answer
MERV 13 captures 90 percent or more of particles between 1 and 3 microns against MERV 8's under 20 percent, which is the band that carries most pet dander and a good share of cooking particles. The step up costs airflow, so it is worth it when the system can take it and the house has a reason: pets, allergies or smoke.
| MERV 8 | MERV 13 | |
|---|---|---|
| 0.3 to 1 micron | not rated | 50 to 74.9 percent |
| 1 to 3 micron | under 20 percent | 90 percent or more |
| 3 to 10 micron | 70 to 85 percent | 90 percent or more |
| Typically used in | the default upgrade filter in most homes | the usual recommendation for wildfire smoke, where the system can take it |
| Catches | mould spores, dust mite debris, pet dander, cement dust | smoke, bacteria carrying droplets, most cooking and candle particles |
Amazon Basics 20x20x1 Air Filter 6-Pack, MERV 11 AC Furnace Filters, Dust, Pet, Allergen Control, Electrostatic (Actual Size: 19.75 x 19.75 x.75)
Furnace filters are bought by the case and changed on a schedule, so the price per filter matters less than how often the system needs a fresh one.
Check the size printed on the frame of the filter already in the return before ordering, since the nominal size and the actual size differ by a fraction of an inch.
What changes between MERV 8 and MERV 13?
The visible difference is in the finer bands. The usual recommendation when a manufacturer will not sanction anything denser. It is a real filter and it barely touches airflow. The class most smoke guidance points at. Check the blower first, because it is also where static pressure starts to matter.
Going from MERV 8 to MERV 13 is a real change in what reaches the room, and it is also a real change in how hard the blower works. Both are true at once, and the right answer depends on the system rather than on which number is larger.
When the step up is worth it
Three situations justify it: somebody in the house reacts to something airborne, there are pets, or smoke arrives from outside for part of the year. Outside those, the cheaper filter changed on time often beats the denser filter left in place too long.
The one hard constraint is the equipment. If the system manufacturer sanctions a maximum filter rating, that is the ceiling, and a variable speed blower will tolerate more restriction than a single speed one.
What it does to running cost
Denser filters cost more per unit and load faster, so the annual cost rises on both sides. Against that, a restricted system runs longer to reach the same temperature, and that shows up on the power bill rather than in the filter aisle.
Furnace and HVAC filters
- Filterbuy
Filterbuy 20x20x1 Air Filter MERV 8 Dust & Allergy Defense (4-Pack)
$29.96 Check pricePrices change often - Aerostar
Aerostar Air Filter 20x20x1 MERV 8 AC Filter, HVAC, Furnace Filter, 6 Pack
$32.45 Check pricePrices change often
Common questions
Is MERV 13 much better than MERV 8?
In the 1 to 3 micron band, which is where pet dander and a good share of cooking particles sit, yes. MERV 13 is rated at 90 percent or more against under 20 percent for MERV 8. Whether that matters depends on whether anything in your house is producing particles in that band.
Will the denser filter damage my system?
Not by itself. What causes problems is a denser filter left in place past the point where it is loaded, which raises static pressure, cuts airflow and makes the blower work harder. Step up in filter rating and step up in how often you change it at the same time, and check what the equipment maker sanctions.
Which one for wildfire smoke?
The denser of the two, if the system can take it. Smoke particles are mostly under one micron, which is the band where the higher rating has a measurable advantage. A portable machine with a HEPA filter in the room you occupy is the stronger move, and running both is better than either alone.
Do these ratings mean anything for portable purifiers?
Not directly. MERV describes filters for ducted systems under ASHRAE 52.2. A portable purifier is rated on clean air delivery rate under AHAM AC-1, which measures the whole machine rather than the media. Comparing a MERV number with a CADR number is comparing a filter to a machine.
How often should either be changed?
Look at the filter rather than the calendar. A quarterly check is a sensible habit, with a change whenever the media has gone visibly grey across its face. Homes with pets, dusty seasons or a smoke event will need it sooner, and the denser filter will always be first.