Merv Guide
Filterflow Guide
Which MERV rating is right for your furnace filter?
MERV (Minimum Efficiency Reporting Value) tells you how well a filter captures airborne particles. Higher MERV = more filtration, but also more airflow restriction. Picking the right one depends on what you want to filter and what your HVAC system can handle.
What does MERV mean?
MERV is an industry-standard scale developed by ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers). It rates filters on a 1–16 scale based on their ability to capture particles of different sizes — measured in microns.
Filterflow offers the two MERV ratings that fit typical rental-property HVAC: Merv 8 and Merv 11. We cover Merv 13 below for comparison — and explain why we don't recommend it for most rentals. Anything below Merv 8 (fiberglass throwaway filters) doesn't meaningfully filter air; anything above Merv 13 restricts airflow too much for typical home HVAC.
MERV comparison
| Merv 8 | Merv 11 | Merv 13 not offered — see below | |
|---|---|---|---|
| Captures | Dust, lint, pollen, dust mites | + Pet dander, mold spores, fine dust, auto emissions | + Smoke, bacteria, viral carriers, very fine particulates |
| Particle size | 3.0 – 10 microns | 1.0 – 3.0 microns | 0.3 – 1.0 microns |
| Best for | Standard residential use, budget-friendly | Allergy sufferers, pet owners, families with kids | High-end homes, immunocompromised tenants, wildfire areas |
| Airflow restriction | Lowest | Moderate | Higher — verify HVAC spec |
| MPR equivalent | ~600 | ~1000–1200 | ~1500–1900 |
| FPR equivalent | ~5 | ~7 | ~10 |
MPR (Microparticle Performance Rating) is 3M's proprietary scale. FPR (Filter Performance Rating) is Home Depot's. Both correlate roughly to MERV but aren't standardized industry-wide.
How to choose
Start with Merv 11 if you're not sure
For most rental properties, Merv 11 is the sweet spot. It catches the particulates that matter for indoor air quality (pet dander, fine dust, mold spores) without restricting airflow enough to strain a typical residential HVAC system. It's the rating we recommend by default.
Choose Merv 8 if cost is the priority
Merv 8 is the budget option. It still meaningfully filters air — capturing dust, lint, pollen, and dust mite debris — but doesn't catch the finer particles. If you have tenants with no specific air quality concerns and you're optimizing for cost, Merv 8 is the practical pick.
Why we don't offer Merv 13
Merv 13 captures very fine particles — smoke, bacteria, viral carriers — but its airflow restriction can strain older or undersized furnaces, and across a rental portfolio you rarely know every system's spec. A clogged Merv 13 restricts airflow even further between swaps. For the properties Filterflow serves, Merv 11 delivers most of the air-quality benefit without the HVAC risk — so we stock Merv 8 and Merv 11.
Sourcing Merv 13 elsewhere? Verify your HVAC can handle it. Higher MERV ratings restrict airflow, which can strain older furnaces or oversized systems. Check the HVAC manufacturer's spec sheet first. Symptoms of an over-restrictive filter: short cycling, longer run times, or unusual sounds from the blower.
Common MERV questions
Is a higher MERV always better?
No. Higher MERV captures more particles but restricts airflow more, which can stress your HVAC system. The "best" MERV is the highest your system can comfortably handle. For most homes, that's Merv 11.
Can I switch MERV ratings between subscription shipments?
Yes. Change the MERV setting in your account, and the next shipment will reflect the new rating. No fee, no commitment.
Will a higher MERV make my heating bills go up?
Marginally, yes. A more restrictive filter forces your HVAC to work slightly harder. The difference is usually small (a few dollars per month at most), but if you're noticing significantly higher bills after switching to a higher MERV, your system might be straining and a lower MERV is the right call.
How often should I change my filter?
For 1-inch filters, every 1–3 months is typical (3–6 months for 4-inch). Clogged filters both filter worse and restrict airflow. Filterflow ships a year's supply up front and texts your tenant on the cadence you choose, so swaps actually happen on schedule.
What about Merv 14, 15, or higher?
These ratings exist but are designed for commercial HVAC systems with much higher airflow capacity. Installing them in a residential furnace is almost always a bad idea — the airflow restriction overwhelms typical home systems.
Ready to subscribe?
Pick your filter size, choose your MERV rating, and we'll handle the rest. A year of filters in one shipment, SMS reminders on your cadence, one-tap install confirmation.
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