Thermal disinfection - what is it and how does it work?

Thermal disinfection is one of the most important weapons for fighting legionella within the house installation. How it works, what conditions there are and where it is no longer 100% effective, is explained here.

Temperature sensitivity of germs

Legionella can survive only in a very narrow temperature range. Below 21° C and above a temperature of 55° C, they can not survive in most cases. In large germ groups, however, it is still possible to survive individual groups of individuals in the border area of ​​these temperatures.

Many other dangerous germs are sensitive to temperature. Above a temperature of around 70° C practically no pathogenic germs can survive. For this reason, the decoction of water is so effective against the germ load.

Function of thermal disinfection

Thermal disinfection is practically a decoction of the water within the pipes, but at a lower temperature than during the cooking process. This disinfects the interior of contaminated pipes.

A regular thermal disinfection in the area of ​​the hot water system is provided as a so-called Legionella circuit in most devices for hot water production. However, it fulfills its purpose only to a limited extent, since an automatic temperature increase to over 70° C alone is not effective.

If not all outlet openings and fittings are opened, and the temperature increase is not at least 3 minutes, the thermal disinfection is ineffective!

Limitations of effectiveness

From the thermal disinfection only those areas of the domestic water installation are covered, which are actually flowed through by the hot water. Especially in spur lines disinfection is not given - there relatively large Legionellenkulturen survive unscathed.

Sting lines are also particularly vulnerable to legionella, because legionella generally prefer areas with little water movement, and need for their propagation.

Preventive thermal disinfection

As preventive thermal disinfection one refers to the measures, which concern the usual plant operation. Here the current standards require that the operating temperature must always be above 50° C. Ideal are values ​​of about 60° C.

For large systems with a capacity of 400 liters or more, daily heating to at least 60° C is required, but over 70° C is recommended. This Legionella should be already combated preventively.

Risk cold water systems

In Germany, the cold water temperature is usually around 15° C. In individual cases, however, it can lead to a warming of cold water to over 20° C. If values ​​of 25° C are exceeded, Legionella can also accumulate in the cold water pipes. If the temperature remains above 20° C, there is also a risk of infection via the cold water pipes.

Tips & Tricks

The outlet temperature from the taps should be measured during thermal disinfection. If there is still positive evidence, it must be chemically disinfected.

Video Board: mechanical washer / thermal disinfection basics