Proper ventilation in Corona times – 9 helpful tips

The SARS-CoV-2 coronavirus continues to cause countless infections worldwide. And the following still applies: The risk of becoming infected with the coronavirus is higher indoors than outside. It is all the more critical to ventilate them regularly to reduce the concentration of potentially virus-containing aerosols in the air and, thus, also the risk of infection with COVID-19.

But when, how often and how long should you ventilate, what role do room size and number of people play, and to what extent do room cleaners help? We give brief instructions on how to ventilate appropriately in times of Corona.

General tips for correct ventilation

Regardless of the premises, activity and number of people, a few general rules for correct ventilation must be observed: 

• You should always ventilate immediately after one of the people present has coughed or sneezed.
• A tilted window is not enough. Instead, it would help if you opened the window wide. This is the so-called shock ventilation.
• There should also be cross-ventilation by creating a draft by opening several windows or doors opposite one another. This is the quickest way to exchange used air.
• Since proximity to a person infected with SARS-CoV-2 plays a role in infection, compliance with the minimum distances should always be guaranteed despite regular ventilation, for example, at family celebrations or in the office.

Ventilate your home correctly.

In an apartment with a typical size for the number of residents without visitors, the room should be ventilated every hour for about 10 to 20 minutes with the window wide open. Creating a draft by opening several windows or doors (cross ventilation) is optimal. If there are significant temperature differences inside and outside in winter, airing the room for three to five minutes is sufficient. When airing out, the walls cool down less quickly. That is why it makes more sense from an energy perspective than the alternative of ventilating with the window tilted for longer.

If you have visitors, it should also be ventilated regularly and, if the weather allows, even throughout the entire period with a wide-open window.

Ventilation during sport

When you exercise, your breathing rate increases. This means an infected person expels more viruses into the air they breathe in less time. The sporting activity of people in the room also moves the air, which means that aerosols can spread more quickly.

If sport is done in a room, it should be aired about five times an hour for about 10 minutes. It is better to ventilate continuously. However, if you are sweating heavily, you should avoid developing a cold draft to avoid catching a cold.

Ventilation in classrooms

With the usual classroom size (about 60 square meters) and number of students (20 to 30 students per class), the room should be ventilated for at least ten minutes after each lesson with expansive open windows. If the break after a lesson is only five minutes, you should also ventilate the room during the lesson. If the classroom doors go to a room without windows, such as an interior hallway, it is better to keep them closed. Otherwise, aerosols can spread there.

Proper ventilation in the office

The same applies in the office: regular airing is the be-all and end-all. At least once an hour, there should be 10 to 15 minutes of intermittent ventilation, ideally also cross ventilation. The more people are sitting in a room, and the smaller this room is, the more frequently it should be aired. Especially in winter, however, the temperature perception of individual team members is often very different – if one is still warm with the window open, the other is already freezing. In this case, CO2 measuring devices can help set regular ventilation periods.

CO2 meters

CO2 measuring devices or CO2 traffic lights use sensors to measure the concentration of carbon dioxide in the room air. The CO2 content is given in ppm. The unit ppm stands for “parts per million” or “shares per million” in German. This is what the different traffic light colours mean:

• If the CO2 traffic light is green, this usually corresponds to a value of less than 1,000 ppm.
• Yellow indicates a value between 1,000 and 2,000 ppm.
• If the CO2 traffic light is red, the C02 content in the air is at least 2,000 ppm. Then, at the latest, it should be ventilated.

CO2 measuring devices can help to train correct ventilation behaviour.

air cleaner

The benefits of mobile room air cleaners are discussed repeatedly in the context of the coronavirus pandemic. Certain air purifiers can help filter viruses like SARS-CoV-2 from the air. These include room air cleaners with so-called High-Efficiency Particulate Air (HEPA) class H13 or H14 filters. In general, it is advisable to obtain comprehensive information about the devices’ requirements before purchasing an air purifier. For example, the Association of German Engineers (VDI) offers a corresponding overview.

However, room air purifiers should only be used in addition to regular ventilation rather than as a replacement, as their performance depends heavily on exact placement, airflow, and the number of people present. If positioned incorrectly, air filters can even contribute to the air contaminated with virus particles being better distributed in the room through turbulence. In addition, the minimum distance should continue to be maintained since air purifiers cannot protect against infection if two people come into close contact, even if they are used correctly.

Qualified personnel should replace The filters at regular intervals (usually every six to twelve months).

air conditioners

Air conditioners that have a fresh air supply reduce indoor viral loads. However, if the systems only run in recirculation mode, the air in the room is only cooled and not exchanged. Instead, the air in the room is swirled around, which is why such air conditioning systems can even help to increase the risk of infection, as a Chinese study found out. Air conditioning systems with a recirculation function should, therefore, at least have a Class H13 or H1 High-Efficiency Particulate Air (HEPA) filter to filter viruses out of the air.

However, it is essential to know that air conditioning systems in Germany usually have a fresh air supply since the installation of air conditioning systems without this function is somewhat unusual in this country.

In addition, it is sometimes possible to retrofit air conditioning systems in such a way that they have an air-purifying effect. Ventilation systems are equipped with UV-C emitters (ultraviolet light). The UV light can render bacteria and viruses such as the coronavirus harmless. However, the UV-C light must not come into direct contact with the skin or eyes, as it can damage them.

It is, therefore, better to air the room regularly.

Dress warmly while airing.

If it’s cold outside, the temperature inside can drop significantly when airing out. Cold alone does not cause illnesses, but if the immune system is weakened, freezing can increase susceptibility to viruses. Therefore, the following applies: dress warmly and, if in doubt, wear your winter jacket again or wrap yourself in a blanket.