When shopping for an air purifier, you'll inevitably encounter the term "HEPA filter." It's become the gold standard in air purification, but what exactly does HEPA mean, and why does it matter? Understanding HEPA technology will help you make an informed decision when choosing an air purifier for your Australian home.
In this guide, we'll break down everything you need to know about HEPA filters—from how they work to the different grades available, and what to look for when making a purchase.
What Does HEPA Stand For?
HEPA stands for High-Efficiency Particulate Air. The technology was originally developed in the 1940s as part of the Manhattan Project to capture radioactive particles. Since then, HEPA filtration has become essential in hospitals, laboratories, aerospace, and increasingly in residential air purifiers.
A true HEPA filter must meet a specific standard: it must capture at least 99.97% of particles that are 0.3 micrometres (microns) in diameter. To put this in perspective, a human hair is approximately 70-100 microns in diameter, so we're talking about particles that are invisible to the naked eye.
The 0.3-micron size is known as the Most Penetrating Particle Size (MPPS). Particles of this size are the most difficult to capture because they're too large to be effectively caught by diffusion but too small to be easily trapped by impaction or interception. If a filter can capture 99.97% of these challenging particles, it will actually capture an even higher percentage of both larger and smaller particles.
How HEPA Filters Work
HEPA filters don't work like a simple sieve. Instead, they use a complex mat of randomly arranged fibres—typically made from fibreglass—to capture particles through multiple mechanisms:
Interception
When a particle follows an airstream close to a filter fibre and comes within one radius of the fibre, it touches the fibre and is captured. This mechanism is most effective for medium-sized particles.
Impaction
Larger particles can't easily change direction when the air curves around a filter fibre. Their momentum causes them to collide directly with the fibre and stick to it. This is how larger dust particles and pollen are typically captured.
Diffusion
The smallest particles (less than 0.1 microns) don't follow the airstream smoothly. Instead, they move erratically due to collisions with gas molecules—a phenomenon called Brownian motion. This random movement increases the probability they'll hit a filter fibre and be captured.
Electrostatic Attraction
Some HEPA filters have an electrostatic charge that attracts particles to the fibres. This enhances capture efficiency, particularly for very fine particles.
Understanding HEPA Filter Ratings
Not all HEPA filters are created equal. In Europe and Australia, HEPA filters are classified according to their efficiency rating. The most common ratings you'll encounter are:
- H10: Captures 85% of particles at 0.3 microns
- H11: Captures 95% of particles at 0.3 microns
- H12: Captures 99.5% of particles at 0.3 microns
- H13: Captures 99.95% of particles at 0.3 microns (True HEPA)
- H14: Captures 99.995% of particles at 0.3 microns (Medical Grade)
For home use, H13 filters are generally considered the sweet spot—they offer excellent filtration efficiency without the higher cost and reduced airflow associated with H14 filters. H13 is what most experts mean when they refer to "True HEPA."
True HEPA vs. "HEPA-Type" Filters
Here's where you need to be careful as a consumer. The term "HEPA-type," "HEPA-like," or "HEPA-style" is not regulated in the same way as "True HEPA" or "H13 HEPA." Manufacturers can use these terms for filters that don't meet the strict HEPA standard.
A HEPA-type filter might only capture 85-90% of particles, which sounds impressive until you realise it's letting through 10-15 times more particles than a true HEPA filter. When shopping for an air purifier, always look for products that specifically state "True HEPA," "H13," or "H14" to ensure you're getting genuine HEPA filtration.
Marketing terms like "HEPA-type," "HEPA-like," "HEPA-style," or "99% HEPA" often indicate filters that don't meet the true HEPA standard. Always verify the specific filter classification before purchasing.
What Can HEPA Filters Remove?
True HEPA filters are highly effective at removing a wide range of airborne particles, including:
- Dust and dust mites: Common household allergens that trigger respiratory issues
- Pollen: From grasses, trees, and flowers—a major allergen in Australian spring and summer
- Pet dander: Tiny flakes of skin shed by cats, dogs, and other animals
- Mould spores: Particularly relevant in Australia's humid coastal areas
- Bacteria: Many bacteria are within the size range HEPA filters capture
- Some viruses: While individual viruses are smaller than 0.3 microns, they often travel attached to larger particles
- Bushfire smoke particles: PM2.5 and larger particles from smoke
What HEPA Filters Cannot Remove
It's important to understand the limitations of HEPA technology. HEPA filters are designed to capture particles, not gases or odours. They cannot effectively remove:
- Volatile organic compounds (VOCs): Gases from paints, cleaning products, and new furniture
- Odours: Cooking smells, tobacco smoke odour, or pet odours
- Carbon monoxide: This dangerous gas passes right through HEPA filters
- Radon: Another gaseous pollutant that HEPA can't capture
For these pollutants, you'll need an air purifier that combines HEPA filtration with activated carbon filters, which are specifically designed to adsorb gases and odours.
HEPA Filter Maintenance
To maintain optimal performance, HEPA filters require regular replacement. Most manufacturers recommend replacing HEPA filters every 6-12 months, though this varies based on usage intensity and air quality in your area. During bushfire season or in dusty environments, you may need to replace filters more frequently.
Signs that your HEPA filter needs replacement include:
- Reduced airflow from the purifier
- Increased noise levels as the motor works harder
- Visible discolouration of the filter
- Persistent odours despite the purifier running
- Filter indicator light on models with this feature
Some air purifiers have washable pre-filters that protect the main HEPA filter and extend its life. Regularly cleaning these pre-filters according to manufacturer instructions can help maintain efficiency and reduce ongoing costs.
When comparing air purifiers, factor in the ongoing cost of replacement filters. A cheaper purifier with expensive replacement filters may cost more over time than a pricier model with more affordable filters. Check filter prices and expected lifespan before purchasing.
Choosing the Right HEPA Filter for Your Needs
For most Australian households, an H13-rated True HEPA filter provides the best balance of efficiency, airflow, and cost. Here's a quick guide based on your specific needs:
- Allergy sufferers: H13 HEPA is highly effective for pollen, dust mites, and pet dander
- Bushfire smoke protection: H13 or H14 HEPA, ideally combined with activated carbon
- General air quality improvement: H13 HEPA is more than sufficient
- Immunocompromised individuals: Consider H14 medical-grade filtration
Conclusion
HEPA filtration remains the most proven and effective technology for removing particulate matter from indoor air. By understanding the different grades and what true HEPA means, you can make an informed decision when purchasing an air purifier. Look for H13 or higher ratings, be wary of vague "HEPA-type" claims, and factor in filter replacement costs when budgeting for your purchase.
With the right HEPA air purifier, you can significantly reduce allergens, dust, and other particulate pollutants in your home—creating a healthier environment for everyone.