To ensure that church heaters do not become virus slingshots, important points must be observed when heating and ventilating. Information is now compactly compiled in an information sheet.
In almost all areas of life, we are currently adjusting our habits to avoid the spread of the coronavirus. When it comes to the use of churches, it is also important to act differently than usual.

Meanwhile, aerosols have been recognized as a transport route for coronaviruses. In churches, the accumulation and distribution of aerosols that may be loaded with coronaviruses can be reduced. And this is done by changing heating and ventilation.

Although this limits the possibilities of heating the churches, moderate temperature control for the service, albeit at lower temperatures, is still possible.

In an information sheet, we have compiled the relevant information for heating and ventilating churches in a compact form. These do not replace the legal regulations of the federal government and the federal states. Please also inform yourself there about the current status. According to current knowledge, we are thus acting responsibly and church services are also possible in the Corona winter of 2020/2021. This letter also gives you some further information.

All recommended measures can be summarized in three main strategies that can be used to reduce the spread of coronaviruses:

• Relative humidity in the room for use at 50 to 60 percent
• Reduction of air movements during the divine service
• Short but intense ventilation after the service

In addition, we ask you to continue to observe all other proven hygiene rules, such as the distance rules.

The parishes are obliged to keep themselves up to date with the current status of the legal regulations of the federal government and the respective federal state.

Relative humidity in the room for use at 50 to 60 percent

Relative humidity of 50 to 60 percent reduces the infectivity of the coronaviruses contained in the aerosols. The reason for this is the salinity in the aerosol.

The relative humidity can usually be directly influenced by the room temperature. If the air is warmer, the relative humidity decreases, if it is cooler, it rises.

Newer heaters usually have humidity sensors that can be read for control. Or they are equipped with a humidity priority circuit. In this case, the new humidity limits should be programmed here.

Alternatively, the humidity values can be controlled with a simple humidity-temperature measuring device. In addition to the instantaneous value, they usually also record the maximum and minimum values, so that a rough assessment of the room climate is possible. This will probably result in a temperature of around 10 to 12 degrees Celsius.

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Reduction of air movements during the divine service

Meanwhile, infection via aerosols certainly is one of the main ways of infection. The distribution of aerosols must therefore be counteracted as far as possible. Due to their large volume, church rooms now offer the opportunity for a wide distribution of aerosols even in the higher regions of the room, which has advantages in the short use of the space for the divine services. Unfortunately, however, one cannot be sure where the aerosols are transported and whether they are transported back to the visitors’ region by the air movements.

In the heating season, we are therefore faced with the problem that heaters and especially hot air heating cause this air circulation in the room. Therefore, heating systems should be switched off about 30 minutes before using the room. The air can then calm down in good time before the visitors arrive. Underfloor heating, wall temperature controls, and seat cushion heaters may be operated continuously, as they hardly cause air currents or even counteract them.

Until now, it was customary to keep a church at a basic temperature during the week and to raise the air temperature for worship. However, since the walls have very large inertia, they usually remain at the basic temperature and heat up very slowly. This temperature difference between air and wall is another motor of air movements in space. Therefore, either a temperature increase for the service should be avoided or the heating control should be set so that the temperature is reached about two days before the service. With several services per week, it may therefore make sense to maintain the reduced temperatures throughout.

For many types of rooms, such as classrooms and offices, it is recommended to ventilate thoroughly during use. However, this is not transferable to church rooms. Here, effective air exchange is not possible due to the low ventilation cross-sections and the often unfavorable architecture for transverse ventilation. Rather, open church doors and windows lead to unwanted air movements and a decrease in relative humidity. Therefore, it should not be ventilated during the service.

In many churches, there are heating rods arranged under the windows. These window heaters counteract downdrafts in cold outside weather. So they reduce the air circulation in the room. Therefore, they should be operated for worship.

Short but intense ventilation after the service

Even if in many churches a far-reaching air exchange is difficult, ventilation is the most effective way to reduce the virus load in a room. Therefore, this way should be used in any case. For this purpose, all doors and windows should be opened as wide as possible after the service to enable real ventilation (cross ventilation).

However, it is not allowed to ventilate for too long during the heating season, because cold and dry outside air causes the relative humidity in the church to drop sharply. However, this must not fall permanently or far below 50 percent in order not to damage the equipment, such as the organ. Here, too, the humidity sensor of the heater or a simple humidity-temperature measuring device can provide reference values.

Some churches have window sashes that can be controlled automatically or a warm air heater with modern control technology and outdoor air connection. Both techniques usually have sensors that record and compare both the outdoor and indoor climate. In these cases, it makes sense to use the system in favorable air conditions for targeted air exchange or conditioning the room climate to the range of 50 to 60 percent relative humidity.