Are H13 Air Purifier Filters Always Better?

When buying an air purifier, “H13 medical-grade HEPA” has become an almost standard marketing claim. But I have to tell you: H13 is not a good choice for a Room air purifier.

The filter grade describes the ability to retain particles in a single pass, but it is not a complete representation of the purifier’s final performance. The actual effectiveness of a purifier depends on the total amount of clean air it delivers per unit of time. Between the two, there is still the variable of airflow. H13 filters have high resistance, which seriously affects airflow and thereby reduces the purification speed of the device.

I. Filter Classification

The current international standard ISO 29463 (harmonized with EN 1822) divides high-efficiency filters into EPA (E10–E12), HEPA (H13–H14), and ULPA (U15–U17). Classification testing is based on the most penetrating particle size (MPPS, approximately 0.1–0.3 microns), that is, the range where filtration efficiency is lowest and particles penetrate most easily.

Common grades:

From E11 to H13, efficiency increases from 95% to 99.95%, which appears to be a huge improvement.

II. The Cost of High-Grade Filters: Higher Pressure Drop, Lower Airflow

Why is filter efficiency higher? Because the fibers are finer, the packing density is greater, and the pores are smaller. From the perspective of aerosol filtration theory, this enhances diffusion deposition, interception, and inertial impaction, but the byproduct is higher pressure drop.

The GAEF report points out that the pressure drop of H13 is “usually about twice that of E11.”

With the same fan, higher pressure drop will result in lower air flow. 

III. Why Can an Air Purifier with an H13 Filter Actually Have Lower Purification Capability?

An air purifier is designed to intercept as many solid pollutants as possible in the same amount of time, so the air in the room can be as clean as possible, not to make each pass of air as clean as possible.

For example:

• An air purifier model uses an H13 filter: it filters 99.95% of solid pollutants in each pass, with an airflow of 400 m³/h. It can therefore remove solid pollutants from approximately 399.8 cubic meters of air per hour.
• Replacing the H13 filter to E11 filter: it filters 95% of solid pollutants in each pass, with an airflow of 500 m³/h. It can therefore remove solid pollutants from approximately 475 cubic meters of air per hour.

Therefore, the air purifier perform better with the E11 filter. 

The actual purification capability of a purifier is determined by two variables: airflow and single-pass filtration efficiency—not by single-pass filtration efficiency alone. If single-pass filtration efficiency is too high, it will affect airflow. We must use a more balanced filter, that is, a filter with both relatively high resistance and relatively high single-pass efficiency, rather than simply requiring that filtration efficiency be as high as possible.

AirFanta’s room air purifiers were all tested with different filter grades during the design stage. The final filter grade was chosen to ensure that the unit can provide the maximum CADR. This is also an important reason why AirFanta’s air purifiers can provide such a high CADR in such a small size and at such low power.

IV. Where H13 Filters Are Needed: Laminar Flow Purification and Clean Air Bubbles

H13 is not useless. It is suitable for laminar flow air purifiers, not typical whole-room circulation air purifiers.

For the difference between these two types of air purifiers, see: 

“Room Air Purifiers vs. Personal Air Purifiers: It’s Not About Size, It’s About Approach”

The goal of a whole-room circulation air purifier is to repeatedly draw the air in the entire room through the filter and use CADR and indoor mixing to reduce the average concentration. A laminar flow air purifier has a different goal: it needs to create an air bubble that is as clean as possible at the air outlet or in the breathing zone, rather than purify the entire room. In this case, the core metric is no longer the whole-room air exchange rate, but the cleanliness of the air coming out of the outlet itself.

In this scenario, single-pass filtration efficiency becomes critical.

The outlet air concentration of E11 is about 5% of the room concentration; the outlet air concentration of H13 is only 0.05% of the room concentration. The two differ by about 100 times. For scenarios requiring a localized clean environment, this gap is decisive.

Conversely, airflow is not better when it is larger here. Laminar flow purification relies on a stable, low-turbulence airflow boundary. If the air speed is too high, the jet Reynolds number increases, the boundary shear becomes unstable, and dirty air from the surroundings will be entrained, destroying the edge of the clean air bubble. Therefore, H13/H14 are more suitable for medical laminar flow hoods, biosafety cabinets, clean benches, localized clean air bubbles, and similar scenarios, rather than ordinary household whole-room purification.