How warm does the heating water actually have to be in order to be comfortable at home? When it comes to heat pumps, the flow temperature plays a decisive role — not only for well-being, but also for efficiency. Find out why a few degrees can make the difference in this article.

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What is the flow temperature of a heat pump?

The flow temperature of a heat pump is the temperature at which the heating water flows into the radiator or floor heating system. It is crucial for efficiency because heat pumps consume significantly less electricity at low temperatures. The lower the flow temperature, the more efficiently and cost-effectively the heat pump works.

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Which factors influence the flow temperature?

The flow temperature of a heat pump depends on several factors relating to the heating system, the building envelope and user behavior.

• Type of heating surfaces: Panel heating systems such as floor or wall heating systems require lower flow temperatures (30 to 40 °C) than classic radiators. In general, the larger the heating area, the lower the temperature requirement.
• Thermal insulation of the building: Well-insulated buildings lose less heat, which means that lower flow temperatures are sufficient. In unrenovated old buildings, higher temperatures are necessary to compensate for heat losses.
• Hydraulic balancing: A correctly balanced heating system distributes heat evenly. As a result, the flow temperature can be reduced without individual rooms remaining undersupplied.
• Heating curve adjustment: The heating curve determines how much the flow temperature rises when the outside temperature drops. A flat curve reduces the average flow temperature and saves energy.
• User behavior: If you want permanently high room temperatures or ventilate frequently, you increase the heating requirement and thus the necessary flow temperature.

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What are the usual flow temperatures for heat pumps?

Typical flow temperatures for heat pumps are between 30 and 55 degrees Celsius. Heat pumps work particularly efficiently in this temperature window. Higher temperatures result in higher power consumption and significantly reduce the plant's annual performance factor (JAZ).

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Which flow temperature is optimal for heat pumps?

The optimal flow temperature for heat pumps is 30 to 40 degrees Celsius. Heat pumps work particularly efficiently in this area, as power consumption remains low and environmental heat is used in the best possible way. The lower the flow temperature, the higher the efficiency and the lower the heating costs.

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Does a high flow temperature make sense?

High flow temperatures are generally not appropriate for heat pumps, as they are low-temperature heating systems. From about 55 degrees Celsius decreases efficiency by around 2 to 3% per additional degree. This results in significantly higher power consumption and poorer annual performance figures. Efficient heating is only possible at low temperatures.

The following is the effect of the flow temperature on that of an air-water heat pump:

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Which heat pumps can flow 70 to 80 degrees?

Heat pumps with a flow temperature of 70 to 80 degrees are so-called high temperature heat pumps. These include CO₂ heat pumps, devices with two compressors (cascade operation) and hybrid heat pumps with gas or electric auxiliary heating. These systems achieve high flow temperatures but are less efficient, as electricity consumption increases sharply as the temperature rises. The annual performance factor is significantly lower than that of classic low-temperature heat pumps.

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How is the flow temperature of a heat pump set correctly?

The correct setting of the flow temperature is crucial for efficient and trouble-free operation of the heat pump. It is carried out in several steps:

1. Calculate heat load: A specialist company determines the heating capacity required for the building. This results in the necessary flow temperature to supply all rooms adequately.
2. Adjust heating curve: The heating curve regulates how much the flow temperature rises when the outside temperature drops. A flat curve saves energy, but should be adjusted so that all rooms remain warm.
3. Perform hydraulic adjustment: The adjustment ensures uniform heat distribution in the building. As a result, the flow temperature can be reduced without loss of comfort.
4. Check heating surfaces: Large heating surfaces such as floor heating systems or low-temperature radiators require lower temperatures. Higher temperatures are required for small or old radiators.
5. Fine adjustment during operation: In practice, the flow temperature is readjusted. If the room temperature drops, the heating curve can be slightly increased. If it stays too warm, it can be lowered.

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At what flow temperature can a heat pump be installed?

In principle, a heat pump may be installed if the required flow temperature below 55 degrees Celsius lies. This value is considered a guideline for economic and efficient operation.

You can determine whether this requirement is met with the 55 degree test check:

1. Turn the heating down to 55 °C flow temperature — adjust to the existing heating system.
2. Wait a few winter days — ideal for outdoor temperatures below 0 °C.
3. Check room temperatures — If all rooms remain pleasantly warm, a heat pump is generally suitable.
4. Keep a log — Note whether there are cold zones or loss of comfort.

If the test is positive, nothing stands in the way of a heat pump. If it is negative, measures such as changing radiators or adding insulation can help.

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Why is the flow temperature of the heat pump important for efficiency?

The lower the flow temperature, the more efficiently the heat pump works. Even a difference of 20 degrees is clearly noticeable: At 55 °C, efficiency is around 14% lower than at 35 °C. If you want to save money in the long term, you should lower the flow temperature — with suitable heating surfaces, good insulation and an optimised heating curve.

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