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Important for the formula-based separation of hot water costs in the heating bill

The Determining the hot water temperature in central heating systems This is crucial for a fair distribution of heating and hot water costs. While temperatures above 60°C are often mentioned, they are rarely technically realistic. An incorrect temperature reading can lead to significant billing errors.

Why is the hot water temperature important?

For central heating systems that supply both space heating and hot water, the total costs must be divided into heating and hot water costs. If there is no separate heat meter, the formula from the Heating Costs Ordinance applies.

A key factor in this is the Hot water temperatureIf it is set too low, the heating costs artificially increase. If it is estimated too high, the hot water costs rise disproportionately. Both lead to a unfair cost distribution.

Typical average temperatures are between 50 °C and 60 °C.

Where can the hot water temperature be read?

The Ways to determine the hot water temperature depend on the type of system:

Small, older central heating systems:

  • No thermometer for hot water available
  • Boiler temperature (70–90 °C) is often mistakenly used as hot water temperature.
  • Temperature is usually neither adjustable nor directly readable.

Small, modern facilities:

  • Hot water adjustable via regulator (usually 55–60 °C)
  • No separate display, but the controller setting is usually reliable.

Large heating systems:

  • Hot water temperature is usually visible and adjustable on a thermometer.
  • Temperatures Temperatures above 60 °C are considered unlikely.
  • Values ​​above this limit usually indicate a confusion with the boiler temperature.

Estimating hot water temperature – what to do if there is no display?

According to Section 9 Paragraph 2 Sentence 2 Heating Costs Ordinance Is the hot water temperature allowed? be appreciated, when direct measurement is not possible. In such cases:

  • Recommended estimate: 55 ° C
  • This assumption is considered to be technically sound and legally justifiable.

Why hot water should not be below 60 °C

A common tip for saving water – lowering the water temperature below 60 °C – is not recommendableBackground:

  • Temperatures below 60 °C are favorable Legionella growth
  • Legionella bacteria are only reliably killed at temperatures above 60 °C.
  • Modern devices (manufactured from 1993 onwards) do not allow for a lower setting anyway.

Legal reference:

A cooling of 5–10 °C before tapping is normal, therefore: average temperature around 55 °C

According to the DVGW worksheet W 551: At the water outlet of the water heater, at least 60 °C can be achieved

More about Legionella testing

Conclusion: What matters when determining temperature

A correct one Determining the hot water temperature in central heating systems This is essential for a fair distribution of heating costs. Incorrect information – whether too high or too low – leads to incorrect billing results and unnecessary hassle.

recommended action

  • Use no boiler temperature as hot water temperature
  • Use existing controllers or thermometers on the system.
  • If a reading is not possible, estimate standardized at 55 °C
  • Ensure compliance with legal requirements regarding Legionnaires' prevention

Author

Title page of the handbook on heat cost accounting

Quelle: Handbuch der Wärmekostenabrechnung | Frank Peters Minol Messtechnik W. Lehmann GmbH & Co. KG, 2019

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