Coway 400s Video Script

So is the Coway 400S the Best air purifier in the world? -we’ll will soon find out. What is its outstanding feature? Also I am going to show you a way of testing an air purifier which will start to make you think differently about particles in the air in your home. And finally what is the Coway like to live with and should you buy it?

So as you can see it is a fairly big unit – it measures 23 inches tall by 15 inches wide by 15 inches deep and weighs 25 pounds

The filter covers come off like this –

Then the pre-filter is fairly easily removed like this –

The prefilter is to remove large particles that may block the HEPA filter and to prolong the life of the HEPA filter. As usual it is the only washable filter. True HEPA filters are not washable.

Now we can see the carbon filter which removes chemicals from the air-

The CARBON FILTERS in this air purifier contain 1.5 pounds of carbon pellets – you can see them here.

Many air purifiers have much less carbon than this in their filters – here is a typical fibrous filter coated with carbon – you can see that there is much less carbon in this type of filter

Obviously the more carbon there is in the filter the more effective the air purifier will be at removing molecules chemicals from the air.

On the other side of this filter is the HEPA FILTER which removes particles from the air –

A HEPA 13 filter is specified to remove 99.97% of airborne particles but unusually this filter is also specified to remove 99.8% of ultrafine particles. Ultrafine particles when breathed in can enter the bloodstream. It is unusual for manufacturers to specify the filter as removing ultrafine particles and so it gives an indication that this is a very high quality filter.

In normal use the filters will need changing every 12 months.

However particle filtration is only one of the 2 main aspects of air purification, the other is airflow. You can have a great filter but if the airflow is not great your air purifier will not purify much air. Airflow is where the Coway 400S excels and is the best in the world.
The very high AIRFLOWS that can be achieved with this air purifier are due to having an inlet on each side of the machine.
Here is the other inlet with exactly the same configuration of filters-
This effectively doubles the filter area. So this machine has the highest airflow of almost any air purifier on the residential market. Its peak CADR is 417 cubic feet per minute enabling it to serve a room of 642 square feet assuming the height of the ceilings is the standard 8 feet.
That it achieves this at a noise level as low as 51db is quite remarkable.

Apart from the filters themselves, the SEALS around them are very important. This is because if the seal lets air bypass the filter then most of the air will tend to go “WHOOSH” [GESTURE] through this low resistance channel and relatively little will then go through the high resistance filter itself.
This will make the whole air purifier much less effective.

To put this in context when we consider the specifications of the HEPA filter we are really considering the efficiency down to the nearest 0.1% or less. A defect in the seal may lead to a 10% reduction in efficiency with dirty air bypassing the filter and mixing with the clean air that has gone through the filter. So an inefficient seal can potentially make 100 times the difference of choices about the efficiency of the filter.

The seals on the Coway 400S are not simply the filter pressing against the body of the machine as they are in some air purifiers. The filters have this rubber edging which helps make the seal airtight.

This is the quietest air purifier per unit of air flow on the market. The higher the airflow there is through the air purifier the lower the airborne particle count in your room will be. The EPA recommend a reduction in particle counter 80% and for this you will need 4.9 air changes per hour. An air change is when a volume of air in the room has gone through the air purifier once so the whole volume of air in your room needs to go through the air purifier once every 12 minutes, and even that will still leave 20% particles in the air.
So airflow is critical and one of the biggest problems with air purifiers is that because of noise people tend to put the air purifier on its quietest settings unaware that the air is not being adequately filtered. So the fact that the Coway 400S is the quietest air purifier per unit air flow means that you will be less likely to want to turn it down and so end up with air containing too many particles.
I have slept for some time with a Coway 400S on its top fan speed. At first I thought that I wouldn’t be able to sleep with the noise-but I did and it was fine. The thing that put me off at first was the slight increase in high frequency components in the sound compared to some other air purifiers-but it turned out not to be a problem.

The Coway is smart-it can be controlled by phone apps, Alexa and Google Home. Using the phone app you can set schedules for the air purifier to turn on and off. This is useful because an air purifier takes about 30 minutes to bring the particle count down to a plateau. So ideally you should schedule the air purifier to come on half an hour before you enter a room. In this way you will always be breathing clean air.

There is an inbuilt sensor which indicates air quality on the front of the unit here-

Green denotes good quality air and red poor quality air.

I would not advise using the sensor to make decisions about air quality, which after all affects our health. Sensors in most air purifiers are cheap but only give an approximate idea of air quality. Also they cannot detect ultrafine particles in the air at all.
So I don’t recommend running the air purifier in automatic mode where it sets its fan speed according to the sensor reading.

The main running costs are the filters these need to be changed annually.

This is not a cheap air purifier but should last you for years. If you have a large room for the same price you could buy 2 or more cheaper air purifiers for your room which would have the similar effect-although they would probably not be certified to remove ultrafine particles. However this would mean having several air purifiers in one room which may make it look cluttered. Also several air purifiers switched on at the same time may turn out to be noisier.

So the Coway 400S is simply one of the very best air purifiers on the market. If you can afford it and have the space, just buy it. I’ll leave a link in the description below with further details.


[Measurements-Room Air]

First I am going to test the air quality before switching the air purifier on.

To test PM 2.5 fine particles I will use with a Trotec air quality meter. This uses laser diffraction to accurately measure airborne particles down to 0.5 micrometers. This meter costs $1100.

Next to test ultrafine particles I will use a P-Trak Particle Counter. This measures particles down to 0.02 micrometers- that is 20 nanometers. Particles of this size can get straight into our blood streams.
This meter costs about $4000.

The air has XXX ultrafine particles per cubic centimeter.

Now lets put the Coway on for 30 minutes to allow time for the particle count to drop.

So now let’s measure the airborne particles-

[measure with Trotec] so there are XXXX particles in the 0.5um diameter range
and now lets measure the ultrafine particles

[measure with P-Trak] we can see that there are now YYYY ultrafine particles per cubic centimeter

[calculate % reductions]

So there was a ZZZ% reduction in particle count.

To measure the performance of the air purifier I am going to test the air quality at the inlet and outlet of the air purifier.

The most demanding setting for the air purifier filters is when the air purifier is on its maximum setting. So I have put the Coway on its maximum setting.

So first I am going to test the air for fine particles at the inlet of the Coway.
[measure with Trotec]
The air at the INLET has XXX particles in the 0.5 micrometer size range.

[measure with Trotec]
The air at the OUTLET has XXX particles in the 0.5 micrometer size range.

Now measuring the ultrafine particles-
[measure with P-Trak]
The air at the INLET has XXX ultrafine particles per cubic centimeter.

The air at the OUTLET has YYYY particles.

As you can see there are NO/VERY FEW particles in the air coming out of the air purifier.

So the Coway 400S cleans the air very effectively.