Heat pumps are loud, expensive and power guzzlers? Expert explains the 10 biggest mistakes

It is not suitable for apartment buildings, it is loud and only makes sense in new buildings.

There are many prejudices about the heat pump.

An expert explains the biggest mistakes.

Munich - Heat pumps are booming - they are considered the best alternative to heating systems based on fossil fuels and contribute to independence from heating oil and natural gas, whose wholesale prices are currently falling.

Nevertheless, there is probably no other type of heating about which there are as many prejudices as about heat pumps.

The systems are neither as loud nor as vulnerable or expensive as is often assumed.

We spoke to an expert.

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It is not suitable for apartment buildings, it is loud and only makes sense in new buildings.

There are many prejudices about the heat pump.

(icon picture)

© Silas Stein/dpa

The Federal Minister for Economics and Climate Protection, Robert Habeck (Greens), wants to enforce a general ban on oil and gas heating from 2024.

Existing plants are now also in the Vice Chancellor's sights.

Not least because of this, heat pumps are becoming increasingly popular as a heating option.

However, there are still stubborn misconceptions about energy-efficient heating systems.

We spoke to Clemens Dankwerth from the Department of Heating and

 at the Fraunhofer Institute ISE in Freiburg.

Heat pumps are only suitable for new buildings

It is often said that heat pumps are only suitable for well-insulated new buildings.

That's not true.

"Heat pumps work best at low flow temperatures," explains Clemens Dankwerth.

This makes them ideal for tailor-made installation in new buildings and is now used in more than half of all new residential buildings.

Nevertheless, heat pumps can also be installed very well in old existing buildings, for example in the course of a renovation or when replacing the old oil or gas heating system.

"Investigations by Fraunhofer ISE have shown that they achieve good energy efficiency even in rather poorly insulated old buildings.

It only becomes inefficient from a flow temperature of over 50 degrees," says Dankwerth.

In the studies, average annual performance factors of 3.1 were achieved for air-to-water heat pumps.

This means that for every kilowatt hour of electricity, 3.1 kilowatt hours of heat were released.

Heat pumps are noisy

Air to water heat pumps use fans to draw in and blow out air, which creates flow noise.

The compressor can also emit an audible hum, which is caused by the vibration of the heat pump.

However, modern heat pumps are very quiet and have a sound power level of less than 30 dB.

This means that they are whisper quiet in the truest sense of the word.

For comparison: 30 dB corresponds to the volume of whispers, 40 dB to the volume of refrigerators.

"But acoustics is always a subjective perception," says air conditioning technology expert Dankwerth.

"That's why it makes sense to additionally avoid noise development at certain control levers - for example by keeping a sufficient distance from walls and neighbors, with vibration dampers and noise protection hoods".

Heat pumps are expensive

"Although heat pumps appear more expensive to buy at first glance, their investment is worth it in the long run," says Clemens Dankwerth.

Not only are heat pumps supported by state subsidies, which compensate for part of the difference in investment costs.

More good news for consumers: "Compared to other heating systems, heat pumps also have by far the lowest operating costs." In an average-sized single-family house, depending on the development of gas and electricity prices, it can cost between 6,000 and 12,000 euros within 10 years save on running costs.

Heat pumps are power guzzlers

It is true that a heat pump needs electricity to function.

However, the actual power consumption is much lower than is often assumed.

Modern and efficient heat pumps only need about 20 percent of the electricity compared to the heat output generated.

In other words, to generate 100 percent heat, a heat pump only needs a fraction of the electricity.

"The heat pump is practically unbeatable in terms of energy balance," summarizes Felix Doucet from the Competence Center for Renewable Energies and Energy Efficiency at HAW in Hamburg.

His study, which compared heating with heat pumps and hydrogen, also came to a clear conclusion.

If you have your own photovoltaic system, you can even operate the heat pump with your own green electricity.

You might also be interested in:

Heat pump bottleneck: These manufacturers are now the fastest to deliver

Heat pumps are not suitable for apartment buildings

It is a misconception that heat pumps can only be used in detached or semi-detached houses.

Although they are often used in these buildings, in Germany they only cover 59 percent of the total living space.

In order to achieve actual CO₂ neutrality, the other 41 percent of the living space in apartment buildings must also be heated ecologically, "which require much more energy to heat than individual houses," says Clemens Dankwerth.

The international research project LowEx Stock, in which the scientist was involved, has therefore developed various solutions for how heat pumps can be used sensibly in apartment buildings.

For example, centralized heat pump systems for the entire building, a combination of central and decentralized supply, heat pumps for one residential unit or for several residential units, and heat pumps for individual apartments or even individual rooms are possible.

At sub-zero temperatures, heat pumps only provide enough heat as a hybrid heating system 

Modern heat pumps are capable of supplying a house with sufficient heat on their own, certain models even at low outside temperatures down to minus 29 degrees.

But of course, heat pumps can also be used in a hybrid combination to provide additional support in particularly cold times.

"A common method is the combination of heat pumps with heating elements, which are only used at peak loads," explains Dankwerth.

“The heating element is then switched on for maybe 50 hours a year when the outside temperature is minus 15 degrees.”

Heat pumps only work with underfloor heating

It is a persistent misconception that heat pumps are only suitable for buildings with underfloor heating.

"In fact, heat pumps are compatible with both underfloor heating and almost any radiator, with a large surface being an advantage," says Clemens Dankwerth.

"An exception are massive radiators that need flow temperatures of 60 or 70 degrees".

Practically every house can therefore be equipped with a heat pump or converted during renovation.

Heat pumps need a lot of space

Instead of requiring a lot of space, heat pumps are on the contrary a space-saving solution.

In contrast to an oil burner or a gas boiler, they can also be installed outside the home.

When selecting the size of the heat pump, the previous oil or gas consumption is taken into account, among other things, since the effectively required heating energy can be determined based on these values.

Heat pumps can only heat

Heat pumps are real all-rounders.

In addition to providing heating and hot water, they can also be used to cool the room in an energy-efficient way - either actively or passively.

Here, the heat pump circuit is reversed, as in the refrigerator.

Expert Dankwerth advises: "For cooling, care should be taken that the temperature does not fall below the dew point, so that no moisture condenses on floors or radiators.

But a flow temperature of at least 20 degrees ensures that”.

Heat pumps have a short lifespan

A heat pump consists of many different components, some of which have a longer and others a shorter life expectancy.

A sensitive part is the compressor, which is claimed to need replacing after just 10 years.

In fact, with regular maintenance, a compressor can last around 50,000 hours of operation, which corresponds to a service life of 25 to 30 years.

However, there are differences between heat pumps - which draw most of the energy for heating from the ambient air - and geothermal heat pumps.

"Compressor manufacturers now assume a service life of around 20 years," says Dankwerth, "although the geothermal devices last longer because they are subjected to constant temperatures in the ground of 10 degrees less than air heat pumps".

List of rubrics: © Silas Stein/dpa