Different filter classes and standards – and what they stand for
What is behind the different filter classifications? A lot of information, many standards, and little clarity. Let us explain.
In the air purifier market, apples are often compared with oranges. The variety of filters on offer and their advertised cleaning performance is almost as large as the number of manufacturers themselves. So, how can we find a way through this jungle of offers?
It's important to understand a few things:
- First, what are the different standards,
- Second, what do the different designations mean
- And finally, what are helpful tips on how to choose the right air purifier
What exactly does HEPA mean?
- The term HEPA describes more a type of filter than a standard. The term HEPA is an acronym and stands for "High-efficiency particulate air" sometimes also for "High-efficiency particulate arrestance". The term is used by different standards but also by the air purifier industry with different definitions.
Is HEPA in everything that says HEPA on it?
- Yes and no. Usually what is advertised as a HEPA filter will be something suitable for household use. But as HEPA by itself is not a standard, it does not classify what kind of filter it is. Always check for further information like one of the actual classifications used by the industry, which are explained in the following section THE BASICS.
Worldwide there are several different filter classification standards. The main goal of these standards is to create a scale with which different filters can be compared. The focus is on several aspects. Let's have a look at the main three and how they are measured:
Filter efficiency
- A certain volume of polluted air is filtered once through a filter.
- Then, for all particle size groups, the percentage of each that remained in the filter during this single pass is measured.
- The percentage of the particle group that was filtered the least is then the filter efficiency rating of the filter. This is also called MPPS or "Most Penetrating Particle Size".
Filterable range (particle sizes)
- Aerosols containing particles of different sizes are pushed through the filter.
- This makes it possible to measure in which size range a filter provides a certain cleaning performance. This is often combined with measuring the filter efficiency as certain standards have predefined what particle sizes must be used for measuring the filter efficiency.
CADR
- Stands for "Clean Air Delivery Rate" = volume of air that can be filtered in a given time.
- Usually measured in cubic meters per hour (m³/h) or cubic feet per minute (cfm).
Knowing what is behind the different classifications and values allows you to better choose the right product for your needs.
So here is an explanation with 2 examples of what is most important about air purifiers and what you can look for when buying a product:
The various filter classification standards each focus on one of two main factors:
- The minimum filter efficiency
- The maximum volume of air that can be filtered in a given time
Most important for an air purifier is always a combination of these two values:
Very high filter efficiency is only helpful if a high enough volume of air per hour can also be filtered with this efficiency.
- Ex. 1: A filter with 99.95% efficiency in an air purifier with a CADR of 30 m³/h can purify the air in a room of 30 m³ (12m²) only 1x per hour.
- Ex. 2: A filter with an efficiency of 85% in an air purifier that reaches a CADR of 300 m³/h can clean the air in a room of 30 m³ (12m²) 10 times per hour.
The product of example 2 thus brings an overall better cleaning performance for the room size, despite the lower efficiency than the device of example 1.
Filters with very high-efficiency values are of course important for labs, hospitals, and similar facilities as there the room air can not be filtered multiple times to be cleaned but should be cleaned as much as possible in one cycle before entering the room through a ventilation system. With a special focus on microbes, viruses etc.
But for a mobile home use device that is mainly used for filtering dust, pollen, pet dander and smog it's much more important to have a device that can achieve a CADR suitable for the room size you want to use it in, while the filter can be of lower efficiency.
