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Purchasing a heat pump – more efficiency, lower costs

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Strong arguments for moving towards the future of heating –– by purchasing a heat pump, you save heating costs in the long term and protect the environment as well as the climate. Find out here everything you need to know about purchasing Viessmann heat pumps and the options they offer

A heat pump allows you to use environmental energy in an extremely efficient way. This is because that energy –– all of which is available anyway, and free of charge –– is the energy source used to heat the house and domestic hot water to a comfortable temperature. Before homeowners purchase a heat pump, it is helpful to know the answers to a few questions. One concerns the type of heat pump.

Heat pump types – compare before purchasing

In the same way that "car" is a generic term covering many different styles and models, "heat pump" is an umbrella term for heating systems that use the environment as a heat source. The various sources and sophisticated technology enable homeowners to find the heating system that suits them best and that provides them with heat reliably and economically. The following heat pump comparison provides initial guidance on when it is worth investing in a particular type of heat pump. What are the benefits of an air source heat pump and where can a brine/water heat pump be used most economically? You can learn more about the similarities and differences here.


Common features of all heat pumps

As the name suggests, this heating system generates heat by pressurising a gas in a similar way to an air pump. Regardless of which heat source the heating system uses, the refrigerant circuit process is at the heart of every heat pump. Before the ambient heat (air, geothermal energy or water) can be brought to the required temperature, it enters pipes and reaches a heat exchanger through which refrigerant flows. Due to its special material properties, the refrigerant evaporates at low temperatures. The heat generated in the process is too low for use in heating and domestic hot water, which is where the electrically powered compressor comes into play to raise the temperature. You can find out what the entire process looks like in detail in the section entitled How a heat pump works.


Differences between heat pumps

Anyone purchasing a heat pump should familiarise themselves with one of the main differences between the various types: which heat source is used. Ultimately, this also determines where the heat pump is installed. In addition to ambient air, extract air and groundwater, a heat pump can also extract heat from the ground. In the case of an ice energy store, all three heat sources can supply the required energy. Which of these heat sources is more suitable depends on the individual circumstances. Air source heat pumps are used very frequently in practice, which is partly due to their relatively rapid installation. Price also plays an important role here, of course. After all, an air source heat pump is the most economically efficient way of heating with environmental energy.

Air heat pumps are among the most widely installed heat pumps in Germany. This is due both to their simple and rapid installation and to their relatively low investment costs. A conventional air source heat pump extracts heat from the outdoor air and raises it to the required temperature through the refrigerant circuit process. Depending on the model, appliances can be installed either outdoors or indoors. In the case of monoblock appliances installed outdoors, the refrigerant circuit is completely built into the heat pump. The generated heating energy is transported into the building with heating water. With split heat pumps, the refrigerant circuit is separated. The heat is transported by refrigerant line to the interior of the building, where the evaporator heat exchanger is located. This guarantees that the outdoor unit is frost-free, even in the event of a power failure.

A special form of air source heat pump is known as an extract air heat pump. Instead of outdoor air, this heat pump uses the extract air from rooms, which tends to be much warmer. This means that the compressor has less work to do to reach the required temperatures. The air volume is usually limited, however, which means that mono mode operation is not possible. As a rule, these types of heat pump are used for very small heat loads.


When compared to the outdoor air, geothermal heat is relatively high below a certain depth. In addition, it remains constant in winter, even when the upper layer of soil is already frozen. Brine/water heat pumps work very efficiently and achieve a COP of up to 5.0. There are two basic methods to choose from when it comes to extracting geothermal heat. If space is limited, geothermal probes are the best option. These are sunk into the earth vertically or at an angle through boreholes and extract heat from the ground at a depth of 40 to 100  metres.

As an alternative to geothermal probes, geothermal collectors only need a shallow depth of around one to two metres, i.e. below the frost line. On the other hand, they require significantly more space due to their horizontal and large-area installation. You can learn in detail about how the heat is recovered in the section entitled How a brine/water heat pump works.


Groundwater is also an excellent heat source, providing consistently high temperatures all year round. Two wells are required for heat recovery. For the water/water heat pump to work efficiently, the groundwater composition and the water volume must meet minimum requirements.

Which heat pump to buy for which house?

When considering the appropriate type of heat pump, the heat source should never be overlooked. Because, while air source heat pumps are used almost everywhere, operation of a brine/water heat pump does not make sense, or might not even be permitted, in every location. Boreholes are required for the installation of the geothermal probes. In principle, deep drilling is subject to mining law provisions and must be reported to the competent authority.

This also applies to the geothermal probes of brine/water heat pumps, which is why these systems are not appropriate for every home. In addition to the heat source, it is also important to look at which heating system is installed. Hybrid heat pumps, for example, are particularly suitable for radiator heating systems with higher temperatures.

Purchasing a brine/water heat pump without a drilling permit

If homeowners still want to benefit from the advantages of a brine/water heat pump despite the lack of a drilling permit, they can switch to surface collectors. However, these require sufficient free space to be available for their installation. Exactly how large the area needs to be depends on factors such as the nature of the soil and, of course, the heat demand of the house. As a rule of thumb, the collector area should be one and a half to two times as large as the living space to be heated. In addition, the collector area should not be built on, so that the ground can regenerate more quickly with the help of the sun and rain.

As an alternative to surface collectors, consumers can also use trench collectors, which, due to their design, achieve a much higher extraction rate per square metre.


Ice energy store as an alternative

The ice energy store is a special form of heat pump. It works with high efficiency as it combines the three energy sources of ambient air, geothermal heat and solar radiation.

An ice energy store consists of a concrete tank without insulation that is filled with water. Inside are pipe turbulators through which antifreeze circulates. The water serves as the primary heat source and is selectively frozen and thawed. In addition to the heat contained in the ground, a solar air absorber actively supports the defrosting process. Please see the section entitled Ice energy store for the individual steps of this process.  

For installation, the ice energy store requires an area of around four square metres and a depth of four metres as well. An official building permit is not required for this type of system. This makes an ice energy store a viable alternative to a conventional geothermal probe system.


Picture: @ frytkownica /

Benefits of a heat pump

Quiet, reliable and economical. For many people, a heat pump is still the optimal heating system as it uses free environmental energy that is available anyway, and makes it suitable for heating and domestic hot water. In addition, the state actively supports the purchase of heat pumps with attractive subsidies. The benefits of a heat pump essentially fall under three categories: economic, environmental and economic policy.

A few years ago, heating with electricity was still considered uneconomical and unecological because efficiency losses were very high and electricity was mainly produced from coal. Since then, however, most heat pumps have become highly efficient and keep heating costs at a permanently low level. One of the main reasons for this is environmental energy as a heat source. Unlike natural gas and oil, environmental energy is not subject to economic or political fluctuations. Most importantly, it is always available and free of charge.

Further economic benefits of a heat pump are its low maintenance operation and the attractive subsidies available from the state. The section on heat pump subsidies explains how to apply for these.


Another point in favour of purchasing a heat pump is the high level of operational reliability and the possibility of obtaining low cost heat pump electricity. What's more, most Viessmann heat pumps are able to lower the temperature in the warmer months of the year using the active and passive cooling function. Other economic benefits of a heat pump are:

  • No costs for a chimney and flue gas inspector
  • Increase in property value when selling
  • Meets all EnEV requirements for new build and renovated older buildings

Efficiency plays a very important role in the purchase of a heating system. With increasing environmental awareness, however, climate protection is also coming more and more to the fore. If you invest in a heat pump today, you are also making a major contribution to reducing the harmful greenhouse gas CO₂.

Heat pumps uses renewable energy for heating and require only a small amount of electrical energy, which means less need for the mining and combustion of fossil fuels. The CO₂ balance of the electricity used for heating is significantly lower when compared to other fossil heating systems. If green drive power is also added in, a heat pump can operate entirely carbon free.

Statistics also illustrate how the environmental benefits of a heat pump stack up in practice: according to the German Federal Ministry for Economic Affairs and Energy, the use of renewable energy sources in the heating market alone prevented around 37  million tonnes of CO₂ across Germany in 2016. By way of comparison, energy-related emissions in the transport sector amounted to 166.2 million tonnes in the same year.

Aside from the lower investment costs when compared to other heat pumps, air source heat pumps have further benefits. Retrofitting is possible at any time, without having to obtain official approval. Furthermore, an air source heat pump has a very small footprint, making it suitable for both new build and modernisation projects.

If the option of operating a brine/water heat pump is available, homeowners should give serious consideration to purchasing one. Because of their constantly high output temperatures throughout the year, these heat pumps work very efficiently.  

In essence, heat can be extracted from the ground in two ways –– if space is limited, geothermal probes that are sunk deep into the ground are suitable. If, on the other hand, the house to be heated has a sufficiently large garden that is not built on, geothermal collectors offer a sensible alternative. Similar to underfloor heating, these are laid underneath the top layer of soil. From there, they extract heat from the layer of earth and transfer it to the evaporator. In addition to surface collectors, trench collectors are also an option. These require significantly less space.


The "energy transition" is a project launched by the German government with the aim of meeting Germany's energy needs almost exclusively with renewable energies by 2050. Many experts believe that one strategy that can achieve this goal is to combine the electricity and heating markets, as well as transport, also known as sector coupling. In the electricity and heating markets in particular, heat pumps are an important instrument because:

  • Electricity is becoming cleaner due to the expansion of green power plants
  • Surplus power from wind turbines and photovoltaic systems must be used sensibly (power to heat)
  • Current heat pumps operate highly efficiently and can help to relieve public grids

With an increasing share of green electricity in the energy mix, as well as high efficiency, heat pumps work in a more climate-friendly way than heating technologies based on the combustion of fuels. They also ensure a sustainable, renewable heat supply all year round –– and in large quantities. In theory, they can help to harness surplus power from wind turbines and photovoltaic systems, thus ensuring grid stability. For many experts, this all makes the heat pump the perfect technology for sector coupling.


However, there are still some obstacles in the way of implementation. Firstly, the legal framework conditions needed to give operators sufficient legal certainty of favourable energy prices are not in place. Secondly, electricity is still burdened with high taxes and levies. Politicians are being called upon to change the law accordingly as soon as possible. Still, when surveyed, HVAC installers remain optimistic that demand for heat pumps will increase significantly in the coming years.

Before purchasing – heat demand and radiators

Heat pumps not only use different heat sources, but are also available in many output ranges. Before homeowners purchase a heat pump, they should consider at least two aspects – their heat demand and the use of the heat pump. The heat demand will vary depending on the energy status of the building and user behaviour. In order for the heat pump to work as efficiently as possible, it should be designed accordingly.

The other aspect concerns use. A heat pump can be operated in either mono mode or dual mode. While most new buildings can get by with a single heat pump, many home renovators often opt for a combined solution when modernising. Here, the heat pump works with the existing, intact heating system and offers system owners not only a secure heat supply but also an extremely high degree of flexibility in terms of fuel price.

In our advice section, you will find more tips on Purchasing a new heating system.

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The right radiators

For economical operation, it's not just the output that has to be right. The radiators and the building itself should also be as suitable for the heat pump as possible. Two prerequisites for efficient, mono mode operation are radiators that can manage low flow temperatures and favourable building energy values. In practice, underfloor heating combined with a heat pump has proven to be very effective.

The ideal time to purchase

Before homeowners purchase a heat pump, they should consider the timing carefully. To prevent an impact on comfort, it is advisable to choose the warmer months of the year for an expert consultation, purchase, installation and commissioning. This is the time when the demand for heat and domestic hot water is very low.

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