If you've ever tried to buy a paint booth filter and asked "what MERV rating is it?", you've hit one of the most common points of confusion in the industry. The short answer: paint booth exhaust filters usually aren't rated by MERV at all. Exhaust filters are rated by arrestance, intake filters can be rated by MERV, and NESHAP compliance is measured by a separate capture-efficiency standard — the "98% rule." Here's how the three fit together so you can spec the right filter with confidence.
Arrestance — how exhaust (overspray) filters are rated
Arrestance (measured under ASHRAE Standard 52.1) is the percentage by weight of a coarse test dust that a filter captures. Because it rewards stopping large, heavy particles, it's the right yardstick for paint booth exhaust filters — the media that traps paint overspray as air leaves the booth. Quality exhaust media (fiberglass rolls, Andreae accordion filters, paint-arrestor pads, and bag/pocket filters) typically publishes arrestance ratings in the 98–99%+ range. When you're buying an exhaust or overspray-capture filter, arrestance — not MERV — is the number that matters.
MERV — how intake / air-quality filters are rated
MERV (Minimum Efficiency Reporting Value, from ASHRAE Standard 52.2) rates how well a filter captures fine particles across the 0.3–10 micron range. It's built for HVAC and air-quality filtration — the intake side of a booth, where you want clean incoming air for a flawless finish, plus any make-up air or recirculation. A higher MERV means finer particle capture. MERV is meaningful for ceiling/intake media and supply-air pre-filters, where dust in the incoming air would land in your paint. It is not the correct rating for overspray capture on the exhaust side.
The "98% Rule" — what NESHAP 6H actually requires
The rule people mean by "the 98% rule" is NESHAP 6H — the EPA National Emission Standards for Hazardous Air Pollutants for Area Source paint stripping and miscellaneous surface coating (40 CFR 63, Subpart HHHHHH). For spray-applied coatings, it requires each booth to either use a filter technology demonstrated to achieve at least 98% capture (control) efficiency of paint overspray, or use a water-wash (water-curtain) booth. The key point: this is a capture-efficiency requirement verified by a defined test method — it is not a MERV number, and it is measured differently from weight arrestance, even though a good exhaust filter will satisfy both. When a product is labeled "NESHAP 6H compliant" or "≥98% capture," that is the standard it is meeting.
Quick reference
| Metric | Standard | What it measures | Where it applies |
|---|---|---|---|
| Arrestance | ASHRAE 52.1 | % by weight of coarse dust captured | Exhaust / overspray-capture filters |
| MERV | ASHRAE 52.2 | Fine-particle efficiency (0.3–10 microns) | Intake / air-quality / recirculation filters |
| 98% capture (NESHAP 6H) | 40 CFR 63 Subpart HHHHHH | Overspray control efficiency | Regulatory compliance for spray booths |
How to spec the right filter
- Buying an exhaust / overspray filter? Look for a published arrestance of 98% or higher and NESHAP 6H compliance — ignore MERV here.
- Buying an intake / ceiling filter? This is where fine-particle (MERV-style) efficiency matters, because anything the supply air carries can end up in your finish.
- Chasing compliance for an inspection or insurance? You need documentation that your exhaust filter meets the 98% NESHAP 6H capture standard.
Still unsure which filter your booth needs? See our NESHAP 6H compliance hub for manufacturer certificates and state requirements, browse our paint booth filters, or call our team at 800-381-0149 and we'll match you to the right media the first time.
Reviewed by the Spray Booth Shop technical team. Every exhaust filter we stock is selected to meet or exceed the NESHAP 6H 98% capture standard.