Water-to-water heat pump

Water-to-water heat pumps

Ground water as a heat source

Does your region have an ample supply of ground water? If so, it could be an ideal heat source that you can tap into by using a water-to-water heat pump. Read on to find out all about this type of heating system.

01. How water-to-water heat pumps work

This heating system works by extracting heat from the ground water beneath your house and using it for heating. For this to work, this heat pump variant requires two wells:

  • Supply well: Ground water is extracted from the supply well. The heat in this water is used to warm and vaporise the refrigerant in the heat pump. The heat pump then compresses the vapour in the refrigerant circuit to produce sufficient hot water to run the heating system. 
  • Return well: The cooled ground water flows back into the ground in the return well.

Experts call this type of heating a water-to-water heat pump as it transfers heat from the ground water to the heating water.

02. Advantages of water-to-water heat pumps

Ground water heat pumps have several plus points that you should know about:

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Climate-neutral heating

Ground water heat pumps do not emit any CO2 or particulate matter, just like other heat pump heating systems. If you choose a system of this kind, you are investing in a cutting-edge, climate-neutral heating system. Read more

Predictable energy bills

Water-to-water heat pumps only consume electricity and so make you independent of oil, gas or wood supplies. Even if fuel prices rise, your heating costs will stay low. Read more

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Outstanding efficiency

Both the ground and ground water have a constant temperature all year round allowing this type of heat pump to achieve excellent levels of efficiency. Geothermal heat pumps need to transfer heat from the ground to a brine circuit. In contrast, water-to-water heat pumps can use the temperature of the energy source directly without transferring the heat. That is what makes this type of heat pump so outstandingly efficient: it turns one kilowatt hour of electricity into five or six times as much heat. Read more

Low operating costs

Thanks to this exceptional efficiency, the cost of electricity needed to run a water-to-water heat pump is very low.

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Cooling in summer

In the summer, the cool ground water can be used conveniently to air-condition your home.

03. What are the advantages of using ground water?

Water-to-water heat pumps offer a range of benefits but also have a few drawbacks. For instance, not every location has sufficient ground water, and this must be meticulously investigated in advance by experts.

You will need an official permit for the necessary drilling work and for installing the water source heat pump. It is forbidden to use this type of heat pump in water conservation areas, for example. Ground water that contains a great deal of iron and manganese can cause heat pumps to become clogged with deposits. This has an adverse effect on both heating output and efficiency.

Installing a water-to-water heat pump is complex due to the well drilling work and approval process, both of which are also expensive. So this type of heat pump heating is more costly than an air-to-water heat pump or even a gas condensing boiler.


However, the excellent efficiency of water-to-water heat pumps means that they mostly pay for themselves very quickly. As long as the site is thoroughly inspected to ensure that it is suitable for this type of heating, you will have a very modern, efficient and future-proof heating system.


04. Installation sites for water-to-water heat pumps

The ideal installation site for a ground water heat pump is a cellar or utility room as this keeps the distance to the two wells to a minimum. It also makes it easier to protect the lines from freezing. In unfavourable locations, you can alternatively install a water-to-water heat pump with an intermediate brine circuit, although this will impair the system’s efficiency.

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05. Buyers’ tips for water-to-water heat pumps

The same applies to every type of heat pump: heat pump heating systems can only achieve optimum efficiency when combined with radiant panel heating systems. So it is strongly recommended to plan new buildings with underfloor heating or wall-mounted heating elements. For existing buildings, it is ideal if underfloor heating has already been installed. If not, it can be worth thinking about retrofitting a heating system of this kind or using alternatives, such as wall heating systems, ceiling panels or large radiators.

The following checklist shows you how to get the best out of a heating system that uses ground water as an energy source:

The higher the seasonal performance factor (SPF) of a heat pump, the less electricity it consumes. The efficiency of the various models can be compared on the basis of the SPF.

The European Union issues energy efficiency labels for heat pumps. When choosing a water-to-water heat pump, make sure your appliance has an A+++ label.

Using solar power from a photovoltaic system on your home’s roof makes running your water source heat pump particularly economical and self-sufficient with regard to energy. Heat pumps with the SG Ready label specifically utilise excess power from photovoltaic systems.

Every heat pump heating system needs a hot water tank for DHW heating. In most cases, it is also worthwhile installing an additional buffer cylinder for storing heat for the central heating system.

Energy suppliers offer special electricity rates for heat pumps that include shut-off times. Providing sufficient storage volume will allow you to bridge these periods easily.

Combination tanks allow you to store DHW and heating water in one container.

The insulation standards of existing buildings must be fairly good to use systems of this kind. If not, a hybrid solution consisting of a gas condensing boiler and heat pump may be the better choice.

Answers to your questions about water-to-water heat pumps

  • A ground water heat pump needs about 2000 litres of ground water per hour to achieve a ten-kilowatt heating output. A hydrological survey must be conducted in advance to determine whether the substrate can provide enough water.

  • The ground water must contain low levels of dissolved oxygen and have low conductivity. Otherwise, the well will be prone to corrosion and clogging due to the formation of deposits.

  • Local water authorities of cities and municipalities are responsible for monitoring the water and for water management processes, such as approving ground water heat pumps (in Germany).

Water-to-water heat pump

Our recommendation: Heat pump BWW-1

The BWW-1 water-to-water heat pump extracts free energy from the ground. Thanks to their high efficiency all year round, they thus ensure a reliable heat supply.