How Does a HEPA Filter Actually Work?

If you’ve been shopping for an air purifier, you’ve probably heard the term HEPA filter mentioned a lot. But what exactly is it and why is it so effective?

Let’s break it down in a simple, no-nonsense way.

What Is a HEPA Filter?

HEPA stands for High Efficiency Particulate Arrestor, and these filters are designed to remove at least 99.97% of airborne particles as small as 0.3 microns in size. That standard comes from the Institute of Environmental Sciences and Technologies (IEST) so you know it’s not just marketing fluff.

Now, here’s the interesting part: while 0.3 microns is the benchmark size used to rate HEPA filters, they’re actually even better at capturing particles both larger and smaller than that. So you’re getting incredible all-round filtration power.

How Does a HEPA Filter Work?

Particles in the air aren’t all the same size, and they don’t behave the same way either. So HEPA filters are designed to trap them using four different techniques, depending on their size and how they move.

Sieving

This one’s simple: big particles just don’t fit through the gaps between the fibres. Think of it like trying to push a football through a tennis racket it’s not going anywhere.

Inertial Impaction

Particles that are slightly smaller and heavier still get caught. As air moves through the filter, it flows around the fibres. But larger particles can’t follow those curves as easily, so they crash into the fibres and get stuck.

Diffusion

Tiny particles (like viruses or ultra-fine pollution) don’t move in straight lines. They zigzag around randomly and eventually hit a fibre kind of like a game of microscopic pinball. Once they hit a fibre, they’re trapped.

Interception

Then there are mid-sized particles around 0.3 microns that follow the airflow but come close enough to a fibre to get snagged. It’s like brushing past something and getting caught on it.

Why Is a HEPA Filter So Useful at Home?

The air inside our homes can be surprisingly dirty. In fact, it’s estimated that we’re exposed to 72% of the chemicals in our daily lives inside our homes not outside in city streets or at work.

Here’s what could be floating around in your indoor air:

  • Volatile Organic Compounds (VOCs) from paint, furniture, and plastics
  • Formaldehyde from carpets and fabrics
  • Pollen, dust, and mould spores
  • Pet dander and skin particles

If you suffer from asthma, allergies, or sensitive lungs, these invisible pollutants can cause a real problem.

That’s where a good HEPA air purifier comes in. It can:

  • Reduce allergy and asthma symptoms
  • Improve sleep quality
  • Lower the risk of respiratory illness
  • Help you feel more alert and energised throughout the day

And since we spend about 2,372 hours a year sleeping, even just having an air purifier in your bedroom could make a huge difference to your overall health.

In a Nutshell

HEPA filters work hard, using clever, multi-layered methods to trap nearly every type of airborne pollutant that might be floating around your home. If you're serious about clean, healthy air (especially if you have kids, pets, or allergies), investing in a purifier with a genuine HEPA filter is one of the smartest things you can do.

Want help choosing the right one for your space?
Call us on 01207 507444  or just read a few of our other helpful air purifier blogs.

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