The most misused, abused and least understood term in the air purifier world is “HEPA.” There are a few HEPA truths out there, and many HEPA falsehoods. The falsehoods include what a HEPA filter is, what it does, and how it’s made. Let’s start with a few undisputed truths:
- HEPA is a type of air filter; the acronym stands for High Efficiency Particle Arrestance.
- HEPA filters were developed by the US Atomic Energy Commission in the 1950s to efficiently remove airborne radioactive particles.
- HEPA filters are officially defined by US Military Specification 282 of 1956. This specification describes the performance standard of removing 99.97% of 0.3 micron particles at the air flow rate for which the filter is rated.
Over the decades since the atomic age, “HEPA hucksters” have stretched and variously obfuscated the definition of HEPA. Today, most consumer “HEPA” filters bear little resemblance to those original units protecting our soldiers from atomic fallout. You see, real HEPA filters that can actually meet the Mil-282 standard are expensive and painstaking to make. They also create a fair amount of air resistance, requiring large motors and fans to get practical outputs. This means money. When home HEPA filters were found to have health benefits in the 1980s, the consumer HEPA market was born. So the engineering exactitudes of HEPA ran headlong into the penny-pinching ways of the consumer market. The result was predictably disappointing. Here are a few common tricks of the HEPA hucksters:
- Sometime a few years ago somebody started calling 95% filters HEPA filters. I’m not sure how this happened or why it was accepted. I guess 95% kind of looks like 99.97%, except for the inconvenient fact that it allows 166 times more contamination through!
- A critical part of HEPA manufacturing is to completely internally seal the filter material (the media) to the filter frame and to itself. This prevents air from circumventing the material. Somewhere along the line, competitive companies started using 99.97% rated filter media, but not sealing it to save money. They call this 99.97% HEPA, but this is a half-truth at best. The Mil 282 rating is for the complete filter, not just for a section of material. Many consumer grade “HEPA” filters are guilty of this sin.
- As you pump more air through a HEPA filter, the efficiency goes down. Real HEPA filters have a maximum air flow rating, usually expressed in cubic feet per minute. In other words, the size of the HEPA needs to be matched to the size of the purifier. Other companies will use a tiny HEPA with a huge blower and advertise large flow rates, even though the HEPA is overloaded and ineffective. I have been amazed by the tiny size of some of the consumer-grade “HEPA” filters out there that are functionally useless.
So where does all this leave the consumer that wants a HEPA without the huckster? Buy an AeroCure One or AeroCure MD. The real deal Mil spec 282 guaranteed. Not the cheapest, but the truth never is.