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How to choose the best air purifier

All HEPA air purifiers clean air but a little research ensures you are getting the most #cleanair for your money and that it will be effective for the size of YOUR room. We have 3 calculators to help you with your research, plus some top tips


1. Ignore the Marketing Hype

Claims about proprietary technology often aren’t backed up by independent tests. Also, don't be convinced by beautiful blonde families living in all-white homes. Read more about some of the premium options designed to help you part with your money.

Think about whether it is worth the exposure to UV or ozone (ionizer purifiers) when all you really need for clean air is a fan and a HEPA filter

@SmartAirFilters discuss UV purifiers in detail.

Purifiers with particle counters and auto mode may be turning off before the air is clean. Ideally you want it set at W.H.O. levels as ‘acceptable’ levels in China and India are substantially higher than UK are higher (which is double W.H.O. levels)

2. Focus on the numbers

Clean Air Delivery Rate (CADR)

The most important numbers for an air purifier are the room size, which tell you how big a room the purifier can cover (when running on its highest setting) and CADR which tells you how much clean air is coming out of the purifier.

CADR has known flaws, but is the yardstick in which to compare the effectiveness of a purifiers. Some companies won't make this easy to find and will tell you what is wrong with the current system but in absence of a better (and standardised) form of measurement, this number is crucial to help you compare products on an equal footing. So unless your CADR is low, what is the harm in publishing it?

Published CADR figures are based on the the highest setting but due to the noise levels, purifiers are generally run on 'low'. Find out what the actual CADR figure is for the lowest setting to see if it is powerful enough for your space

HEPA grades

Don't get stuck on PM0.3. ALL HEPA filters capture virtually 100% of nanoparticles (including viruses which are around PM0.1). PM0.3 is the smallest size that travels in a straight line so is the hardest size to capture, NOT the smallest! HEPAs are graded on their ability to trap PM0.3 and above and regardless of the grade, will catch virtually all particles smaller than PM0.3.

The higher the HEPA filter grade, the lower the airflow - and you really need a high airflow for clean air. We took the test results of H11 & H12 filters on the Sqair and looked at how this would make a difference in a 12m² room. The H12 captured more PM0.3 particles for the first 5 MINS ONLY! The H11 was far superior because of the high airflow.

Noise levels

If you’re looking for a quieter air purifier, choose one with a higher CADR number needed for your room size and then run it on low.

Worried about outdoor pollution from traffic or wood-smoke?

If you need to filter out fumes from outdoor pollution (traffic, wood-burning etc), you will need a carbon filter. Our purifiers have activated charcoal granules and high airflow - our powerful fans result in just 11% reduction in CADR with a carbon filter. Note that even with the doors and windows closed, outdoor pollution finds a way in and can get trapped indoors.

Calculate the number of Air Changes per Hour (ACH) for your space

Use our ACH calculator to work out how much time it takes to clean the air in your space. Once you have this number, run your purifier on 'high' for at least this long to clean the air once. After this, you can turn it down to a lower setting if noise levels are too much.

Compare purifiers using the clean air 'cost effectiveness calculator'

We have provided tools that let you calculate the the true cost of clean air and the number of air changes an hour you can expect for your room size. These will work with any purifiers, not just ours, so do use them before deciding which purifier to purchase.

3. Know that more expensive DOESN’T mean better

Don’t be fooled into thinking that more expensive purifiers are better. Turns out air purifiers are surprisingly simple – they’re just fans and filters. Smart Air (the manufacturers of our purifiers) started out making and marketing DIY purifiers using a fan and a filter. Here are the test results of two DIY purifiers (different fans, same filters) next to some big names...

DIY purifiers costing just US$30 can clean as much air as more expensive purifiers with their fancy claims. Read more for test data...

Find third-party test data

Not all purifiers have been independently tested but it is worth doing a quick search. If you are a paid member of Which?, check their data otherwise some data can be found on the Smart Air website.

The last word

All HEPA purifiers will clean the air but why settle for 1-2 air changes an hour when you can have 5+ for the same money? In an unregulated industry, research is your best weapon to combat poor indoor air quality.


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