How to choose an air purifier

What is an air purifier?

An air purifier is a device which removes contaminants – such as dust, pollen, pet dander, dust mite faeces, mould spores, traffic pollution, smoke particles and volatile organic compounds (VOCs) – from the air in a room.

Why might you need an air purifier?

An air purifier may alleviate your symptoms if you have asthma, hay fever or an allergy to any one of a multitude of airborne allergens. You might also consider purchasing one if you just generally want cleaner air in your home.

How does an air purifier work?

An air purifier typically draws air in and then uses one or more of the following methods to remove contaminants:

Efficiency Particulate Air (HEPA) filtration

They are constructed from fine fiber-like materials that are folded repeatedly on themselves to create a number of barriers that require air to be pushed through. As the air gets pushed through, the HEPA filters stops and traps all of the unhealthy airborne contaminant. Only fresh air comes out the other side. While HEPA filters are the most effective at trapping particles, the filters occasionally have to be replaced. Be aware that air purifier types with HEPA filters do a poor job at removing smells, chemicals and gasses.

Carbon filtration

Carbon filters force air through a layer of charcoal. Activated Carbon is very good at trapping the things that HEPA is poor at removing. In particular, they are good at neutralizing gases, tobacco smoke, odors and chemical emissions.


Ionisation works by creating a static charge around the airborne contaminants that are floating around your room. Once charged with static, these particles (dust, allergens, pet dander etc,) simply stick to the nearest surface they find. Your air feels fresh because the contaminants are no longer floating around in mid air, but the fact is those contaminants are now firmly stuck to many of the surfaces of the room such as the walls, furniture, carpets and table tops. Nowadays ionisation is generally only found as an added extra on a Hepa Air Purifier

UV sterilisation

While UV does not use a physical filter to suck in and trap harmful particles from the air, it does use a special technology that’s excellent at eliminating germs, viruses and bacteria. UV technology works through the use of a lamp installed on an air purifier. As microorganisms pass by the UV lamp the DNA structure is broken apart. The resulting cellular damage kills off microorganisms. UV air purifiers also aid in improving the quality of air by converting molecules of oxygen and water into hydroxyl and ozone that kills airborne pollutants.

High temperature sterilisation

Destroys bacteria, viruses, dust mite allergens, mold and fungus spores by incinerating them.

Things to consider before you buy an air purifier

What do you want to remove from the air?

Depending on the model chosen, an air purifier is capable of removing the following contaminants:

  • Particles, such as pollen, pet dander, dust mite & mould spores
  • Smells
  • Chemicals & volatile organic compounds (VOCs)
  • Bacteria & viruses

How efficient do you need your air purifier to be?

The efficiency of an air purifier refers to the percentage of a particular contaminant that the air filter is capable of removing or destroying.

How big is your room?

The capacity of an air purifier broadly refers to the number of times it can ‘process’ the air in a room in a given period of time. Many manufacturers will provide a recommended room size for their air purifiers. Some manufacturers also publish a clean air delivery rate (CADR) which indicates how quickly the air purifier cleans the air (higher is better).

Running costs

Running consists for an air purifier typically consist of energy consumption, filter replacement and (with some models) bulb replacement.


Many air purifiers contain a fan and so some noise is inevitable.

What additional features do you want?

Features that might be included in a particular model of air purifier (but not in others) include:

  • Fan
  • Servicing indicator
  • Programmable timer
  • Carrying handle
  • Number of speeds:
  • Ionizer
  • Remote control
  • Dirt sensor
  • Washable pre-filter


Some models of air purifier are accredited by one or more independent organisations. It is worth noting that sometimes manufacturers have to pay for accreditation and may choose not to.

Further reading