HEPA air filter with deep pleated white media in a rigid frame

HEPA Filters: True HEPA, Ratings & Where They Fit

8 min read · Filter Types

A HEPA filter (high-efficiency particulate air filter) is a filter that removes at least 99.97% of particles 0.3 microns in diameter from the air passing through it, according to the US DOE and IEST definition commonly called "true HEPA". In Europe and much of the world, HEPA is graded under EN 1822 / ISO 29463, where classes H13 and H14 are the most specified.

HEPA sits well above the MERV scale used for furnace filters. That extra efficiency comes with much higher airflow resistance, which is why HEPA belongs in portable purifiers, dedicated HEPA units and engineered commercial systems rather than in a standard residential furnace slot. This article explains how HEPA works, how it is rated, how to spot marketing terms that are not true HEPA, and where it genuinely fits.

Quick facts

Typical efficiency True HEPA: ≥99.97% at 0.3 µm; EN 1822 H13 ≥99.95% and H14 ≥99.995% at MPPS
Common depths/sizes Panel 2"–3" (purifiers); 6" and 12" rigid cells and V-style housings (commercial)
Typical applications Portable purifiers, hospitals, cleanrooms, labs, pharmacy compounding, bypass HEPA units
Media Microglass (borosilicate) fibre paper; some synthetic and PTFE membrane media
Typical replacement interval Purifiers: 6–12 months; commercial: by pressure drop, often 1–5 years with good prefiltering
Relative cost High – several times a MERV 13 filter of similar size
Reusable? No – washing or vacuuming damages the media
Best paired with A MERV 8–13 prefilter to extend HEPA life; activated carbon for odours and gases

In this article:

How HEPA filters work

HEPA media is a dense mat of very fine, randomly oriented glass fibres, most of them a fraction of a micron to a few microns in diameter. It does not act like a sieve; it captures particles far smaller than the gaps between fibres. Large particles are caught by impaction and interception, while ultrafine particles below about 0.1 micron move erratically by diffusion and are captured very efficiently.

The hardest size to catch is the most penetrating particle size (MPPS), typically around 0.1–0.3 microns for glass HEPA media at normal face velocities. The 0.3-micron figure in the true HEPA definition comes from that region, so a filter that achieves 99.97% at 0.3 microns performs even better on both larger and smaller particles. Fine dust, smoke particles, mould spores, pollen fragments, pet dander and many bacteria-carrying droplets are all captured.

HEPA ratings and standards

Three rating systems are used in Canada, and they are not interchangeable:

Standard / class Test basis Minimum efficiency Where you see it
True HEPA (DOE / IEST) 0.3 µm particles 99.97% North American purifiers, cleanroom and lab specifications
EN 1822 E10–E12 (EPA) MPPS 85% – 99.5% Efficient particulate air filters, below HEPA
EN 1822 H13 MPPS 99.95% Hospitals, quality purifiers, pharma
EN 1822 H14 MPPS 99.995% Operating rooms, cleanrooms, isolation rooms
EN 1822 U15–U17 (ULPA) MPPS 99.9995% and higher Semiconductor and critical cleanrooms
ASHRAE 52.2 MERV 16 0.3–10 µm, three size bands ≥95% in the finest band Top of the MERV scale – not HEPA

Commercial HEPA filters are often individually scan-tested or leak-tested at the factory and supplied with a test label. ISO 29463 is the international equivalent of EN 1822. Note that MERV ratings stop at 16; HEPA is rated by its own tests rather than as a higher MERV.

True HEPA vs "HEPA-type" and "HEPA-like"

Terms such as HEPA-type, HEPA-style, 99% HEPA or HEPA-like have no standard definition. Products carrying them may capture 99% of particles at 2 microns, which is a far easier test, or simply use media that looks similar. When comparing purifiers or replacement filters, look for an explicit statement of 99.97% at 0.3 microns or an EN 1822 / ISO 29463 class (H13 or H14). Also remember that a filter can only perform to its rating if air cannot leak around it; in cheap purifiers, frame and gasket bypass often matters more than the media itself.

Why most furnaces can't take a HEPA filter

A typical residential furnace blower is designed for an external static pressure around 0.5 inches of water column across the entire duct system, with only a portion of that budgeted for the filter. A HEPA filter in a 1-inch slot would create far more resistance, starving the blower, reducing airflow across the heat exchanger and air-conditioning coil, and risking high-limit trips, frozen coils and higher energy use. Filter racks also rarely seal tightly enough for HEPA efficiency to be meaningful.

Practical alternatives for homes:

  • MERV 13 in the furnace, ideally in a deep 4" or 5" media cabinet, plus a portable HEPA purifier in bedrooms.
  • Bypass HEPA units: a separate cabinet with its own fan draws a portion of return air through a prefilter and HEPA filter and returns it to the duct system. These are designed by HVAC contractors to avoid loading the furnace blower.
  • Portable HEPA purifiers sized by clean air delivery rate (CADR) for the room.

Construction and materials

Commercial HEPA filters use pleated microglass paper held in deep pleats by aluminum or thread separators, or in a mini-pleat pack separated by hot-melt beads. The pack is sealed into an aluminum, galvanized or stainless frame with polyurethane or gel seals, and a gasket or knife-edge fluid seal on the face. Common formats include 12-inch-deep box filters, V-style housings and ceiling-mounted terminal modules for operating rooms. Purifier filters are thinner panels, often with a carbon prefilter layer.

V-bank style high-efficiency air filter with multiple mini-pleat media packs

Pressure drop, airflow and energy

A clean commercial HEPA filter typically starts around 1 inch of water column at rated airflow, with a recommended final resistance often around 2 inches – several times that of a MERV 13 pleated filter. Fans must be selected for this. To keep energy costs manageable, engineered systems stage filters: a MERV 8 prefilter, a MERV 13–14 intermediate filter and the HEPA as the final stage. Prefiltering keeps coarse dust off the expensive HEPA media and can extend its service life considerably. Track pressure with a magnehelic gauge or building automation sensor and change filters when they reach the manufacturer's final resistance, not on a fixed calendar.

Where HEPA fits: applications

  • Hospitals: operating rooms, protective environments, airborne infection isolation rooms and pharmacy compounding areas commonly specify HEPA, following CSA Z317.2 guidance for health care facility HVAC.
  • Long-term care homes: HEPA is common in portable units for resident rooms and outbreak response, alongside MERV 13–14 in the central air handler.
  • Laboratories and cleanrooms: biosafety cabinets, fume-sensitive processes and ISO-classified cleanrooms rely on HEPA or ULPA.
  • Construction and abatement: negative air machines with HEPA filters are used for asbestos, mould and renovation dust containment.
  • Homes and schools: portable HEPA purifiers are a practical tool during Canadian wildfire smoke events, when windows stay closed and outdoor PM2.5 is high. See the Wildfire Smoke Survival Guide.

Installation, maintenance and replacement

HEPA performance depends on the seal. Inspect gaskets for compression set or tears, tighten clamping mechanisms evenly, and never install a filter with damaged pleats or a dented frame. In critical areas, filters are leak-tested in place after installation. Handle filters by the frame only. Do not vacuum or wash HEPA media; it damages the fibres and creates leaks. When removing a loaded filter that may hold hazardous material, bag it in place and follow the facility's disposal procedures. For portable purifiers, replace the HEPA element as the manufacturer recommends, typically every 6–12 months, sooner after a heavy smoke season.

HEPA compared with other filter types

Option Fine-particle capture Fits standard furnace? Best use
MERV 8 pleated Low Yes Equipment protection, general dust
MERV 13 pleated or deep media 50%+ at 0.3–1 µm Usually yes Smoke, allergies, LTC and schools
Rigid cell / V-bank MERV 14–16 75–95%+ No – commercial housings Hospitals, labs, offices
True HEPA / H13–H14 99.95%+ No Purifiers, critical areas, bypass units

Neither HEPA nor MERV media removes gases or odours; for those, see activated carbon air filters.

Pros and cons

Advantages Limitations
✓ Highest standardized particle efficiency ✗ High airflow resistance
✓ Captures smoke, dander, spores and fine dust ✗ Not compatible with most home furnaces
✓ Recognized classes (H13, H14) for specifications ✗ Higher purchase cost
✓ Factory testing available for critical uses ✗ Requires a tight seal to perform
✓ Long life with proper prefiltering ✗ Cannot be washed or reused
✓ No ozone or chemical by-products ✗ No effect on odours or gases

Shop at Canadian Air Filters

HEPA filters · Rigid cell box filters · V-bank filters · Bulk and project orders

Made in Brampton, Ontario and shipped across Canada. Need a size you can't find? Request a custom filter or ask about bulk pricing.

Frequently asked questions

What does true HEPA mean?

True HEPA means the filter captures at least 99.97% of particles 0.3 microns in diameter, the definition used by the US DOE and IEST. Terms like HEPA-type or HEPA-like are not standardized and usually indicate lower efficiency.

Is H13 or H14 better?

H14 is more efficient, allowing roughly ten times less penetration than H13 at the most penetrating particle size. H13 is suitable for most purifiers and many healthcare applications; H14 is specified for operating rooms and cleanrooms.

Can I put a HEPA filter in my furnace?

Generally no. The resistance of HEPA media is far higher than a residential blower is designed for. Use a MERV 13 filter in the furnace and add a portable HEPA purifier or a contractor-installed bypass HEPA unit.

Is HEPA higher than MERV 16?

HEPA is more efficient than MERV 16, but it is rated under different standards. The MERV scale tops out at 16, and HEPA filters are classified by EN 1822 / ISO 29463 or the 99.97% at 0.3 micron definition.

How long does a HEPA filter last?

Purifier filters usually last 6–12 months. Commercial HEPA filters protected by good prefilters can last several years and should be changed when they reach the manufacturer's final pressure drop.

Can HEPA filters be cleaned?

No. Washing or vacuuming damages the fine glass fibres and breaks the seal integrity. Extend life by replacing the prefilter regularly instead.

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