You're shopping for paint booth filters and every spec sheet tells you something different — MERV 8, MERV 13, 95% arrestance, 98% capture. Which one actually keeps you legal under NESHAP 6H? The answer surprises most first-time buyers: MERV and arrestance are HVAC ratings. They don't prove NESHAP 6H compliance.
The three ratings, quickly
MERV (Minimum Efficiency Reporting Value)
Defined by ASHRAE Standard 52.2. Tests filter efficiency at multiple particle size ranges (0.3-10 μm) and reports the minimum performance across those ranges as a single value from 1 to 16 (or 17-20 for HEPA/ULPA). Designed for HVAC and indoor air quality applications.
Arrestance
Defined by the older ASHRAE Standard 52.1 (largely superseded). Measures the percentage of a standardized synthetic test dust captured by weight. Arrestance percentages typically look higher than MERV numbers for the same filter because test dust is coarse and easy to catch. A filter can report 95% arrestance and still be a low-MERV filter.
98% Capture (NESHAP 6H)
The 40 CFR Part 63 Subpart HHHHHH requirement for paint booth exhaust filters. Requires filters to capture at least 98% of paint overspray solids. Tested using ANSI/ASHRAE 52.2-2017 at specific particle-size fractions relevant to spray-atomized paint, or via EPA Method 319. Not the same test as generic MERV rating.
Why high MERV doesn't equal 6H compliant
A common misconception is that a high MERV number automatically satisfies NESHAP 6H. It doesn't. Two reasons:
- Different particle profile. HVAC-graded filters are tested against airborne dust. Paint booth exhaust filters have to trap sticky, atomized paint solids and overspray — a completely different loading pattern that clogs, migrates, and behaves differently in the filter media.
- Compliance is a certificate, not a rating. Per 40 CFR §63.11173(e)(1)(i), the shop demonstrates compliance using "published filter efficiency data provided by filter vendors." The vendor's cert letter — stating ≥98% capture at the required test — is the compliance document. A MERV number by itself isn't.
How to read a filter certification letter
A NESHAP 6H compliance certificate should include, at minimum:
- Manufacturer name + product model number
- Capture efficiency (must be ≥98%)
- Test method used (ANSI/ASHRAE 52.2-2017 or EPA Method 319)
- Application scope (e.g., "paint booth exhaust")
- Date + authorized signature
Keep the certificate on file for 5 years minimum alongside your change-out log. EPA inspectors and insurance carriers will ask for it.
Common mistakes
- Buying MERV 13 HVAC filters as booth exhaust filters. They'll clog fast, migrate, and won't have a NESHAP cert.
- Comparing arrestance % to capture %. They measure different things. A 95% arrestance filter and a 98% capture filter aren't comparable specs.
- Assuming the certificate transfers between models. Each filter model needs its own cert. A cert for "Brand X ceiling blanket, 22g" doesn't cover Brand X's 17g variant.
- Losing the cert. Vendors get inquiries months after purchase — keep the PDF the day you receive it.
Quick reference: which rating matters for what
| Application | The rating that matters |
|---|---|
| Booth intake / ceiling filter (make-up air) | MERV rating + tackified media spec |
| Booth exhaust filter (overspray capture) | NESHAP 98% capture cert |
| Second-stage / pocket / final filter | MERV + vendor efficiency data |
| HEPA / final polish (isocyanate control) | True HEPA 99.97% @ 0.3 μm (or EN 1822 H13+) |
Related
- NESHAP 6H Compliance Hub — brand-by-brand cert letters
- Why the 98% capture standard isn't going anywhere
- Shop exhaust filters — all NESHAP-certified
Have a filter and can't find the cert? Call us — we source cert letters from every brand we carry. (800) 381-0149 · orders@sprayboothservices.net