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Everything you need to know about buying an Air Purifier

Buying an air purifier can be very confusing, especially if it’s your first time and the only thing you know is that you want clean air.

Air purifiers are machines that range from the expensive top of the line full-featured home appliance with WiFi connectivity to very simple and affordable devices that just focus on the main function of removing PM2.5 and PM10 from the air such as our AirCleaner Personal.


No matter how big and complex or small and simple, all purifiers share one common purpose. They have to move a mass of air through a filter and that mass of air has to come out of the machine much cleaner than it was before entering it.

In this article, we will focus on some technical specifications that every manufacturer should present when advertising their products.

We will explain to you in plain terms what every specification means so next time you want to buy an air purifier you can choose exactly the device you need.

Also, if you find that some of these specifications are missing, that’s a sign that the manufacturer or vendor are not presenting all the data that you as a customer should know.

Effective Working Area

The effective working area is the room size that the purifier can effectively clean and it is intrinsically related to the Airflow (explained later), filter efficiency (explained later) and the room size.

The effective working area is the single most important parameter you must look for when looking for an air purifier, as you should buy one that will work well for your room size.

To calculate the effective working area, you need to know the airflow and filter efficiency of the air purifier. If you don’t see these parameters on the specifications table of the product you are intending to buy, the manufacturer or vendor could have just created the effective working area from a random assumption instead of real data.

How we calculated the Effective Working Area of the AirCleaner Personal

From our tests, and ESRC Validation Report, we know the following parameters:

Filter Efficiency = 99.86%
Airflow = 285m3/h or 167.64 cfm

We can now calculate the Clean Air Delivery Rate (CADR) of the AirCleaner Personal:

CADR = Airflow(cfm)*Efficiency
CADR = 173.63cfm*0.9986 = 167.4

Now, according to the Association of Home Appliance Manufacturers, for a room with an 8ft (2.44m) ceiling, the CADR is multiplied by 1.55 to find out the effective working area:

Effective Working Area = 167.4*1.55 = 259.47 sqft = 24.1m2

Working backwards, if you know your room size, you can convert that value to sqft and then divide it by 1.55 to get the necessary CADR.

Room volume = 25m2 = 269sqft
CADR = 269sqft/1.55 = 173

You might have seen that manufacturers give the Effective Working Area in a range, for example, 25m2 to 30m2. That’s because rooms are not normally empty, there are beds, wardrobes and stuff around which effectively reduces the total volume of the room.

Knowing the CADR, can also tell us how long the air purifier will take to clean the room. For example, if we have a 25m2 room with a 2.5m ceiling:

Room volume = 25m2*2.5 = 62.5m3 = 2207.16 cft
Minutes to clean the room = room volume/CADR = 2207.16/167.4 = 13min

It is worth saying that these are purely theoretical calculations and in real conditions, there are factors such as leakage, non-ideal air purifier placement and filter ageing which will affect the final CADR and effective working area of the air purifier.


When looking to get a new air purifier, one of the most important parameters you should look for is airflow.

The airflow shows how much air can the purifier circulate in terms of volume (space) per time.

For example, the AirCleaner Personal has a maximum airflow of 285m3/h. That means that theoretically, in a room with dimensions 12m*12m*2m = 288m3 it will take around 1 hour for all the air in the room to circulate through the purifier.

So, why is this important to know? Because the bigger the room you want to clean, the higher airflow your purifier will need.

AirDeveloppa recommends you to always look for the airflow parameter when buying a new air purifier, otherwise, is like buying a motorbike without knowing how many CCs the engine has!

We have seen some small, portable HEPA mini air purifiers in the market. Because of their dimensions and because they are only powered by 5V through USB, they can only have a small airflow, and the tiny filter must get dirty really quick. This means they can only be effective in very small spaces such as inside of a car.

This is an example of how you can end up buying the wrong product if you don’t know the right information.

How we calculated Airflow

AirDeveloppa measured the airflow of the AirCleaner Personal the following way.

Using a wind speed meter, the wind speed was measured at 3 different points of the exhaust pipe at max speed.

Then, assuming point A covers 85% of the total area, point B covers 5% and point C covers 10%

Average Wind Speed = (9.2m/s*0.85)+(5.1m/s*0.05)+(6.5m/s*0.1) = 8.725m/s

Now that we have the average wind speed, the other parameter we need to calculate is the area of the exhaust pipe:

Area = (pi*(0.11m/2)^2)-(0.001m*0.11m*4) = 0.009m2

Finally, we can calculate the airflow in 1 hour:

Airflow = Average Wind Speed*Area*1h = 8.725m/s*0.009m2*3600sec = 282.69m3/h

Filter Efficiency

The filtering efficiency is a parameter that shows how much of a certain pollutant has the filter effectively removed.

Remember that the purpose of a filter of any kind is to take something, remove an unwanted part of it, and then give you the part of that original something that you really want.

When you make orange juice, maybe you only like the liquid and not the orange bits. You then go and take a filter so you can separate the juice from the orange bits, and as you know, all the orange bits stay with the filter.

An air purifier filter works the same way, but instead of orange juice we have air and instead of orange bits we have PM10 and PM2.5.

To calculate filter efficiency, the initial amount of PM2.5 concentration in a controlled small area is measured. Then the air purifier is turned on at max power and left to do its thing for around 15 minutes. After this time, the PM2.5 concentration is measured again so we can then calculate:

Filter Efficiency = 100*(initial PM2.5 – final PM2.5)/initial PM2.5

How we calculated the Filter Efficiency of the AirCleaner Personal

We didn’t! Because some specialist equipment is required, the Environmental Science Research Center and the Chiang Mai University did it for us.

developpa aircleaner personal report test cmu

To make this test, a fully sealed space with a stable PM2.5 concentration was set up by Dr. Wan Wariya. Then, a PM2.5 sensor with WiFi and data logging capabilities was placed inside to register the PM2.5 concentration levels.

air purifier CMU test

The test results are publicly available and can be downloaded from the AirCleaner Personal website.

From the test results, it can be seen that the filtering efficiency of the AirCleaner Personal is up to 99.86%

Most Common Filter Types


air purifier HEPA filter

The High Efficiency Particulate Air Filter, is the most popular and cost-effective method of filtering air.

They are capable of trapping particles as small as 0.3 microns with an efficiency of 99.97%.

A HEPA filter consists of millions of tiny fibres that form a dense web which traps particles in different ways.

  • Impact: When a particle directly collides with the fibres and gets trapped
  • Interception: when a particle is trapped between two fibres
  • Diffusion: when a particle hits a fibre, reducing its travelling speed, and then is caught by another fibre.

HEPA filters are not only used in air purifiers, but you can also find them in N95 and N99 masks and in vacuum cleaners.

It is important to know that HEPA filters can only trap solid particles. They cannot filter out gases or odours.

Activated Carbon

An Activated Carbon filter is the perfect companion for the HEPA filter. While the HEPA filter is great for capturing solid particles, the carbon filter is used to adsorb gases, in particular Volatile Organic Compounds such as formaldehyde and benzene and odours such as cigarette and fresh paint smell.

The activated carbon filter works under the principle of adsorption, where particles from VOCs and smells stick to the outside of the activated carbon molecule.

Even though it can filter out VOCs and many smells, an activated carbon filter cannot fully remove carbon monoxide. It is also hard to determine when the filter is saturated and needs replacement.

Air Ionizer

Ionizers have become quite popular and can be found in many air conditioners apart from air purifiers.

This technology uses electricity to emit a cloud of negative ions with the purpose of attracting positively charged pollutants in the air. These particles then get stick to surfaces such as furniture and walls instead of flying around.

Ionizer technology is a bit controversial as humans are not made to breathe ionized air and it doesn’t really remove pollutants but makes them stick in surfaces that could end up being your lungs.

Also, they can produce tiny quantities of Ozone in small indoor areas which can be very toxic for human beings.

Power Consumption

What is power consumption and why does it matter to you?

As you probably know, once a month you get a bill charging you for the amount of electrical energy you have used in the last month.

Every electrical appliance, including air purifiers, uses power from the electrical grid. Therefore, the more power your air purifier uses, the higher your electricity bill will be.

AirCleaner Personal has a maximum power consumption of 20 Watts, while other brands with similar performance use around 40W to 50W. How does this compare in actual numbers?

air purifier power consumption

Assuming you pay 5 THB per kWh and have the air purifier running in full power for 3 hours per day, then in 12 months:

AirCleaner Personal = 3h*20W*365d = 21.9kWh*5THB/kWh = 110THB
Competition = 3h*50W*365d = 54.75kWh*5THB/kWh = 274THB

As you can see from the calculation above, you’ll save more than half in your electricity bill and achieve the same performance compared to similarly branded air purifiers.

Also, because the total energy consumption is less, but performance is nearly the same, the AirCleaner Personal is a more energy-efficient “green” device!

Loudness Level

Measuring loudness in decibels allows the user to know how loud or noisy the device can be compared to other common noises we all hear in our everyday life. Here is a dBA chart

Image result for dba level chart

The AirCleaner Personal has a loudness level of 45dBA at low speed and 65dBA at maximum speed. As it can see from the graph above, that’s equivalent to the average home noise or a human conversation.

Input Voltage

When you plug an electrical device into the wall, depending on where you are in the world, the voltage might be 110V or 220V and with a frequency of 60Hz or 50Hz.

Some electrical appliances such as fridges, air conditioners or fans can only work with one voltage and frequency.

The AirCleaner Personal has a universal power supply and it works with all standard voltages and frequencies, therefore you can take it anywhere you go in the world!

Electrical Certifications

In order to legally sell electrical products, these have to undergo some regulatory testing and achieve certifications that indicate that the products conform with health, safety, environmental protection standards and electromagnetic compliance.

In Europe, one of these certifications is called CE while in the USA is called FCC.

The AirCleaner Personal power supply has both CE and FCC marking and certifications.

Final Word

Hopefully, after reading this article, we have cleared most of the fog when it comes to selecting an air purifier based on your needs and specifications of the device.

If you would like to enjoy affordable clean air, please check our air quality products brand website, AirDeveloppa or the Facebook Page.


Home Air Guides
Air Purifiers Ratings
Smart Home Guide
Allergy and Air
Explain That Stuff
Breath Quality

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