Guide
True HEPA vs HEPA-Type: What's the Difference?
By Dr. Alex Chen · Updated 2026-03-10
A True HEPA filter captures at least 99.97% of particles at 0.3 microns — the standard defined by the US Department of Energy. A HEPA-Type or H13-style filter may capture 95–99% of particles at that size, falling short of the actual HEPA threshold. For meaningful air quality improvement, True HEPA is the only filter that meets the actual standard.
What Makes a Filter "True HEPA"
The term HEPA comes from the US Department of Energy's definition: a filter must remove at least 99.97% of particles that are 0.3 microns in diameter from passing air.
This is not arbitrary. The 0.3 micron threshold represents the most penetrating particle size (MPPS) — the point at which particles are hardest for a filter to capture. Larger particles (>0.3 µm) are captured more easily by interception and impaction. Smaller particles (<0.3 µm) are captured more easily by diffusion. At exactly 0.3 µm, these capture mechanisms are at their minimum efficiency, making it the toughest test.
True HEPA filters are tested and certified to meet this standard.
HEPA vs HEPA-Type: The Critical Difference
| Filter Type | Capture Efficiency | Particle Size | Certification |
|---|---|---|---|
| True HEPA | ≥99.97% at 0.3 µm | 0.3 µm and larger | DOE standard / independent testing |
| HEPA-Type / H13-style | 95–99% at 0.3 µm | Varies by manufacturer | Self-reported, no standard |
| HEPA-Like / H11 | ~95% at 0.3 µm | Larger particles better | Marketing term, no standard |
The gap between 95% and 99.97% sounds small but is significant in practice. At 95% efficiency, a filter lets through 50,000 particles per million. At 99.97% efficiency, it lets through only 30 particles per million — a 1,667× difference in particle penetration.
How HEPA Filters Actually Work
HEPA filters use three capture mechanisms simultaneously:
- Interception — Particles >0.4 µm follow air streamlines and stick to fibers on contact
- Impaction — Particles >0.4 µm with enough momentum hit fibers and stay there
- Diffusion — Particles <0.1 µm move randomly (Brownian motion) and hit fibers by chance
The efficiency dip at 0.3 µm occurs because particles in this range are too small for efficient interception/impaction and too large for efficient diffusion.
What "HEPA-Type" Actually Means
"HEPA-Type" is a marketing term, not a standard. When a manufacturer says their filter is "HEPA-Type" or "HEPA-style," they are saying it works similarly to HEPA but does not meet the actual 99.97% at 0.3 µm threshold.
Red flags in marketing:
- "HEPA-like" or "HEPA-style" — not certified
- "Captures 99.99% of particles" without specifying size
- "H13 rated" — H13 is European, not US DOE
- No AHAM Verifide certification
Why True HEPA Matters
- Allergen sufferers: Dramatic reduction in allergen exposure
- Asthma patients: Fewer particle triggers means fewer flare-ups
- Immune-compromised individuals: Every reduction in pathogen exposure matters
- Smoke and pollution events: PM2.5 and ultrafine particles cause measurable health effects
How to Verify You're Getting True HEPA
- Look for AHAM Verifide certification
- Check for DOE standard language — "Meets or exceeds DOE HEPA standard"
- Verify particle size in claims — "99.97% of particles at 0.3 microns" is the full standard
- Be wary of vague claims — "Medical-grade" and "hospital-quality" are not regulated terms
Frequently Asked Questions
Is True HEPA worth the extra cost? Yes, for anyone with allergies, asthma, pets, or living in areas with poor air quality. The particle penetration difference is significant for health outcomes.
Can HEPA filters capture viruses? Yes. HEPA is highly effective for respiratory droplet particles (>1 µm) that carry viruses. Influenza viruses are 0.1–0.2 µm; COVID-19 particles are 0.06–0.14 µm — at the edge but still captured by True HEPA.
What's the difference between H13 and True HEPA? H13 is a European classification (EN 1822) requiring ≥99.95% efficiency at 0.1–0.2 µm. It's actually slightly higher than US DOE True HEPA in some particle ranges. Both are excellent.
How often should I replace my HEPA filter? Every 6–12 months depending on usage and air quality. Heavy use (pets, smoking, high pollution) requires more frequent replacement.