The Sars-CoV-2 coronavirus spreads primarily via aerosols: mixtures of air with solid or liquid particles suspended in the air. Large aerosol particles, which are produced when you cough or sneeze, for example, quickly sink to the ground, while small particles – for example from breathing and speaking – float in the air for many hours. If a person is infected with the corona virus, they can exhale large quantities of virus-carrying aerosols in a short time. Effective air purifiers lower virus levels to less risky levels. In combination with regular airing, the effect is even greater.
Why the air purifier test is worthwhile for you
- Testergebnisse. Reviews for seven current air purifiers, including devices from Ideal, Philips and Xiaomi. Among other things, the filter effect against aerosol particles and against pollen and – using formaldehyde as an example – air pollutants was tested. The air filters in the test cost between 171 and 455 euros. The test winner is one of the inexpensive devices. You will also receive results from the previous test on seven air purifiers, most of which are still available.
- Kaufberatung. Also consider the annual running costs for electricity and replacement filters before you buy. Stiftung Warentest calculated the cost of each air purifier in the test. They range from 58 to 220 euros per year.
- Heftartikel. If you unlock the topic, you will have access to the PDF for the test reports from test 3/2020, test 2/2021 and test 1/2022.
Corona: Good effect with new filters
In order to measure the filter effect for aerosols, the testers conducted paraffin oil droplets with a diameter of 0.12 millionth to 1 millionth of a meter into the test chamber. They were similar in size to aerosol particles that can carry the Sars-CoV-2 virus. With fresh filters, all devices collect airborne aerosol particles well. We converted the measurement results from the test chamber to a sample room with 16 square meters, 2.50 meters high and without people. In this room, the concentration of paraffin oil particles in the air drops by 90 to 96 percent after 20 minutes. They all clean the air in this room completely at least four times an hour, as required by experts from the Federal Environment Agency (UBA) for mobile air purifiers.
The effectiveness of the air purifiers in the test decreases
During operation, however, the effectiveness of the filters decreases. The testers simulated an aging of about four to five months. Only four candidates still collect aerosol particles well even with a used filter. With one device, the concentration of virus-sized particles in our sample room fell by only 57 percent, and the air exchange rate was less than twice an hour.
Airing and filtering provide the best protection
Forced ventilation exchanges used air, the virus load caused by an infected person remains permanently low if a suitable air purifier is also used. CO2 meters and traffic lights indicate when it is time to ventilate. Sufficient distance and FFP2 masks also prevent direct infection, for example through the cough cloud of an infected person.
Airing plus filtering provides the best protection. The graphic shows – depending on the behavior of those present – the number of viruses in a 16 square meter, 2.5 meter high room in which there is also a highly contagious person: Without ventilation and air filters, the virus load in the room increases steadily. If the room is ventilated for five minutes every 20 minutes, the number of viruses decreases, but then increases again until the next ventilation. It remains permanently low with ventilation plus the use of an effective air purifier. © Stiftung Warentest
Three filters for the air
Filter systems are usually constructed like this: Under the housing, a pre-filter (1) catches coarse fluff. Then a filter made of fine fibers (2) catches aerosol particles and pollen. The third filter (3) with activated carbon is designed to bind odors and gaseous compounds such as formaldehyde.
Example. Construction of a filter system. © Stiftung Warentest / René Reichelt
Air purifier in the test
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Test results for 7 air purifiers 01/2022
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Test results for 7 air purifiers 03/2020
Pollen quickly disappeared by over 90 percent
In addition to aerosol particles, air filters remove pollen from the air. With the test winner, the concentration of pollen in our sample room drops by 95 percent in ten minutes. People with allergies can usually breathe a sigh of relief.
Tipp: You can read all the information about hay fever and the corresponding medication and aids in the special medication for hay fever.
Running costs from 58 to 220 euros per year
The electricity costs per year depend on the daily running time and the respective fan level. With eight hours of daily operation at the highest level, the annual electricity costs are between 22 and 60 euros. Added to this are the expenses for replacement filters. The instructions for use recommend very different filter change intervals. One provider may recommend a new filter after three months, another only every three years. The operating costs for the tested devices range from 58 to 220 euros per year.
Still available air filters from the previous test
In the previous test of air purifiers in March 2020, we tested the filtering effect of the devices against pollen, formaldehyde and cigarette smoke. According to the provider, the test winner from back then is still available unchanged. In the follow-up test, the device also filtered aerosols well – even with an aged filter.