Cold winter days put heating systems to the test — but how well does a heat pump do when the thermometer drops below zero? Many homeowners doubt whether it heats efficiently even in frost. In this article, you will learn how heat pumps really work in winter and what is important.

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How well does a heat pump work in winter?

One heat pump works in winter by extracting heat from outside air, soil or groundwater even at sub-zero temperatures and using it for heating. A refrigerant absorbs environmental heat and evaporates. The compressor increases the pressure and therefore the temperature of the refrigerant. This heat is transferred to the heating system in the house via a heat exchanger. The refrigerant then liquefies again and the cycle starts all over again.

Depending on the heat source, a distinction is made between:

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All systems are suitable for winter, but differ in efficiency and effort.

Is a heat pump efficient in winter?

A heat pump is efficient in winter and achieves an annual efficiency factor (JAZ) of 2.5 to 4.5 — depending on the type and conditions. Efficiency depends on the type of heat pump: Ground and water-to-water heat pumps are more efficient than air heat pumps because their energy source (soil or groundwater) stays warmer in winter. Other factors include insulation, heating surface type, flow temperature and the correct setting of the system.

Does an air heat pump also work at -15°C?

An air heat pump works even at -15 °C and can still generate heat from outside air even at -20 °C. However, efficiency decreases at very low sub-zero temperatures because less environmental heat is available. In such cases, an integrated heating element usually steps in and ensures the required heating output.

How much power does the heat pump produce at sub-zero temperatures?

At sub-zero temperatures, heat pumps deliver heat reliably, but produce up to 30% less output than at mild temperatures. Air-water heat pumps in particular work less efficiently at -10 to -20 °C. Output decreases because the temperature difference between outside air and the heating system rises. Ground and water heat pumps are less affected because their heat sources offer constant temperatures. The correct dimensions, a low flow temperature and a well-insulated building are decisive for performance in cold weather.

Does electricity consumption increase in winter?

The electricity consumption of a heat pump rises by around 30 to 60% in winter, as the system has to work more at cold temperatures — consumption is highest from December to February.

The following is an example of the monthly electricity consumption of a 10 kW heat pump in a well-insulated single-family house (assumption: annual performance figure 3:

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Heat pump in winter: experiences

Fraunhofer ISE has 2024 interim results from a large-scale Field study on heat pumps published. More than 70 systems in real residential buildings were examined — including many unrenovated old buildings. The result: heat pumps work efficiently and reliably even in winter. Even at outside temperatures below freezing point, a stable supply was achieved. It is particularly noteworthy that the plants in the old building achieved an average annual performance figure (JAZ) of around 2.9 — a value that confirms that they were used economically and energetically.

The use of heating rods was also analysed in the study. The average heating element output of outdoor air heat pumps was only 1.9%. The data shows that heating elements play a minor role in regular winter operation — particularly in well-adjusted and controlled systems with inverter technology.

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How do you avoid problems with the heat pump in winter?

To ensure that your heat pump works reliably and efficiently in winter, you should consider a few key points.

• Set the heating curve correctly: This automatically adapts the flow temperature to the outside temperature.
• Keep the outdoor unit free: Remove snow, leaves, and ice around the unit regularly.
• Check the drain for condensation water: ** A free flow prevents glaciation under the outdoor unit.
• Maintain the heat pump regularly: A specialist company detects faults or wear at an early stage.
• Check insulation and hydraulic balancing: A well-insulated shell and uniform heat distribution relieve the system.
• Check the use of the heating rod: Continuous operation indicates incorrect settings or defects.
• Avoid nighttime subsidence: Large temperature fluctuations cost more energy and reduce efficiency.

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When is a heat pump alone not enough?

A heat pump alone is not sufficient when the heat demand is very high — for example in unrenovated old buildings with poor insulation or in heating systems with high flow temperatures.

In such cases, the heat pump may reach its performance limit, particularly on very cold winter days. Here is a recommended hybrid solution with additional gas boiler or wood heating. Even an incorrectly dimensioned or poorly adjusted system can result in the heat pump not meeting the demand. Careful planning and heat load calculation are therefore crucial.

How reliably does the heat pump heat in winter?

The heat pump heats reliably even in winter if it is correctly designed, adjusted and maintained. Modern systems are designed to work efficiently even at sub-zero temperatures and provide stable flow temperatures. Studies show that a reliable heat supply is possible even in old buildings. This requires good insulation, suitable heating surfaces and correctly adjusted operation. If necessary, the heating element steps in to help — but only rarely. If you rely on quality and specialist planning, you can rely on your heat pump even in the dead of winter.

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