Heat pumps in old buildings: Knowing how!
A heat pump in an old building - is it possible? Many owners of old buildings doubt whether the resource-saving heat pump technology is suitable for their home. But research results show that it is: Heat pumps can also work efficiently in existing buildings. If a few basic requirements are met, nothing stands in the way of a sustainable and economical heating solution in old buildings.
At a glance
- Practical study: Efficient operation of heat pumps is also possible in old buildings.
- Prerequisites for a heat pump: energy refurbishment and good heat distribution are crucial for efficiency in old buildings.
- Advantages and disadvantages at a glance: High investment costs, but lower operating costs and fewer CO₂ emissions.
- Simple test: Check in three steps whether your old building is suitable for a heat pump.
- Which heat pump for an old building? Air-to-water heat pumps and hybrid solutions are ideal for existing buildings. Other, more complex options: Groundwater and geothermal heat pumps.
- Is a heat pump worthwhile in an old building? The cost-effectiveness depends heavily on the condition of the building and the heating requirements, but is a given in many cases.
- Checklist: From advice to heating technology - for a successful heat pump installation in old buildings.
Field test: Efficiency of heat pumps in old buildings
Heat pumps are now standard in new buildings. But what can heat pumps achieve in older buildings? This was investigated in the ‘WPsmart im Bestand’ project by the Fraunhofer Institute for Solar Energy Systems ISE. The Institute for Housing and the Environment (IWU) also reports on findings from heat pump practice in residential buildings in Hesse.
The good news for renovators is that heat pumps also work reliably in older buildings and can be used efficiently and in an environmentally friendly manner. According to both studies, success depends primarily on the quality of the building envelope and heat distribution, and less on the age of the house.
Subjects of investigation:
- In the ‘WPsmart im Bestand’ project: Old buildings constructed between 1850 and 2007 (i.e. 15 to 170 years old), including single-family and multi-family houses that have undergone various types of renovation.
- In the field study in Hesse: 48 existing residential buildings, predominantly single-family and two-family houses of various ages and renovation statuses.
- Outdoor air and ground source heat pumps were used in both studies.
Key findings:
‘WPsmart in existing buildings’:
- Specific heating energy consumption varies greatly depending on the degree of renovation. The energy efficiency of the building therefore influences the efficiency of the heat pump in older buildings.
- Compared to natural gas condensing boilers, CO₂ emissions were 27 to 61 per cent lower according to the calculations.
‘Heat pump practice in existing residential buildings in Hesse’
- Air-to-water heat pumps achieved average annual performance factors of over 3, while ground source heat pumps achieved over 4.6. Even in unrenovated or partially renovated existing buildings, good values were achieved.
- According to both studies, factors such as low flow temperatures, larger heating surfaces and optimised control systems are crucial.
What does this mean for installing a heat pump in your old building?
Both field studies show that heat pumps are also a practical, efficient and environmentally friendly heating solution for existing buildings. Targeted energy-efficient renovation and adaptation of heating technology are key to exploiting the full potential of heat pumps.
Advantages and disadvantages of heat pumps in old buildings
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What requirements must an old building fulfil for a heat pump?
Heat pumps convert environmental energy into heating energy. They achieve the highest efficiency when the temperature difference between the heat source - i.e. ambient air, groundwater or soil - and the required flow temperature of the heating system is low. Compared to conventional heating systems, heat pumps therefore generally operate at lower temperatures, which are usually around 35 to 45 °C. In order to achieve the desired thermal comfort in the rooms, the heat should be efficiently manifolded and retained in the building.
How can this be achieved? Important prerequisites for operating a heat pump in an old building economically and comfortably are
- Insulation: many old buildings have inadequate insulation, which leads to high heat losses. Energy refurbishment with improved insulation of walls, roof and windows keeps the heat in the building better and thus reduces the heating requirement.
- Sufficient heating surfaces: Existing radiators are often designed for high flow temperatures and cannot provide the desired level of thermal comfort with the lower flow temperatures of heat pumps. In this case, it can make sense to increase the heating surfaces, for example by installing underfloor heating, or new radiator technology using special heat pump radiators such as the x-flair for more efficient heat distribution.
- Correct heat pump dimensioning: An exact determination of the heating load is crucial in order to calculate the required output of the heat pump.
- Add other system components: Buffer storage and modern control technology are precisely matched to the heat pump and work together to help increase efficiency. By combining them with a photovoltaic system, self-generated electricity can also be used to operate the heat pump, further reducing operating costs.
Test: Is my current heating system suitable for a heat pump?
The following test can be carried out to check whether the existing heating system in the old building is suitable for operation with a heat pump:
Step 1: The flow temperature of the current boiler is reduced to around 50 degrees Celsius.
Step 2: The thermostats of all radiators in the house are turned up fully.
Step 3: Now check whether the room temperature remains comfortably warm or whether it is too cold.
If the temperature in the house remains comfortable, it looks good for the use of a heat pump in the old building.
Tip: Heat pump radiators for effective heat distribution
If the house is well insulated and the rooms are still not warm enough in the heat pump test, this may be due to the existing radiators. Here, for example, the installation of underfloor heating could increase the heating surface and thus improve heat dissipation.
However, this often costly renovation measure does not necessarily have to be necessary: special heat pump radiators that are optimised for low flow temperatures can replace old radiators without major conversion work. The x-flair, for example, ensures effective heat distribution.
Which heat pump is suitable for old buildings?
The various types of heat pump differ primarily in terms of the energy source used and the installation effort required. The air-to-water heat pump is the most common and usually the most cost-effective solution, especially for older buildings. As no complex excavation work or well construction is required to tap into the heat source, it is easy to install - and is ideal for retrofitting. At moderate outside temperatures, the heat pump also works efficiently in old buildings; on very cold days, additional heating can provide support.
Further options for a heat pump in an old building
- Geothermal and water-to-water heat pumps offer high efficiency, but require larger investments, space and often official authorisations. Due to these challenges, these heat pumps are rarely used in old buildings.
- Hybrid heating systems combine a heat pump with a conventional heating system (e.g. gas heating). This can make sense when using a heat pump in an old building if this alone is not sufficient - or as a first step towards switching to renewable energies.
You can find more detailed information on the different types of heat pumps and their areas of application here.
Installation options in existing buildings
If you want to retrofit a heat pump in an old building, you need to consider the existing structural conditions and the available space. Air source heat pumps offer two installation options and therefore flexibility.
Indoor installation:
- Heat pump is installed inside the house.
- There is space for this in an old building, e.g. in the cellar or utility room - for example, where an old boiler and oil tank have been removed.
Outdoor installation:
- The outdoor unit is installed on the outside of the building or in the garden.
- Sound insulation and sufficient distance from neighbours must be taken into account. However, modern appliances are already very quiet, so there is no noise nuisance for neighbours.
Economic efficiency of heat pumps in old buildings
Is the investment worth it?
The question of whether a heat pump is worthwhile in an old building depends on various factors.
- Costs: Purchase, installation and possible refurbishments must be taken into account. Air-to-water heat pumps are usually cheaper than groundwater or geothermal heat pumps.
- Operating costs: Electricity consumption depends on the efficiency of the heat pump and the individual heating requirements.
- Savings: Compared to oil or gas heating systems, significant savings on energy costs are often possible. This is because the fossil fuels gas and oil are expensive and the CO2 price that is formed for them adds to the costs.
- Subsidies: Government grants and subsidy programmes can significantly reduce investment costs. Find out more about funding opportunities here.
The cost-effectiveness of a heat pump in an old building is therefore largely determined by the condition of the building, the usage behaviour and the available subsidies. In many cases, however, the investment makes financial sense - and also makes a contribution to climate protection.
Checklist: Successfully implementing a heat pump in an old building
- Advice: Commission a specialist company or energy consultant to analyse the heating load and building
- Check and improve the condition of the building: Insulation of walls, roof, cellar, tightness of windows and doors
- Check and adapt the heating system: Test existing radiators in a 50-degree test, switch to underfloor heating or heat pump radiators if necessary
- Select the right heat pump: Match type and output to building and heating requirements, check air-to-water heat pump as standard solution for old building
- Clarify installation options: Plan indoor or outdoor installation of the heat pump, consider space requirements and sound insulation
- Utilise funding opportunities: Check and apply for current grants and loans
- Ensure efficient operation: Use monitoring and control for efficient operation
FAQ
What do you need to consider when switching to a heat pump in an old building?
For a heat pump to work efficiently in an old building, it is important to have good building insulation, suitable radiators or panel heating, and the lowest possible flow temperature. Before installation, a heating load calculation should be carried out to determine the appropriate heat pump capacity and to check the feasibility of installation in the building.
Can a heat pump be operated in an old building with existing radiators?
In principle, it is possible to operate a heat pump in an old building with existing radiators, but many old radiators are designed for high flow temperatures and therefore no longer provide the desired heating comfort at the lower temperatures of a heat pump. Special heat pump radiators such as the x-flair are optimised for low flow temperatures and can replace old radiators without major conversion work. This improves heating comfort without the need for costly renovations.
Can a heat pump be combined with gas heating?
Yes, in older buildings, heat pumps can be combined very well with gas heating systems to form so-called hybrid systems. This combination enables low energy costs and high efficiency, as the heat pump provides heat at moderate temperatures in a resource-saving manner and the gas boiler steps in to provide additional support when needed. An intelligent control system that optimally regulates the entire system is particularly important here. All KERMI heat pumps have such a control system integrated as standard.
What problems can arise with heat pumps in old buildings?
A common problem is so-called cycling, which occurs when the heat pump capacity is oversized. This frequent switching on and off can have a negative impact on the service life of the heat pump.
It can also become a problem if the heat distribution system requires higher flow temperatures, as heat pumps should ideally be operated at maximum flow temperatures of 55 °C. Even an increase in the flow temperature of one Kelvin can reduce the efficiency of the heat pump by around 3%. High flow temperatures also have a negative effect on the service life of the system.
How efficient is a heat pump in an unrenovated old building?
In older buildings that have not been renovated, heat pumps are usually less efficient: poor insulation leads to higher heat losses, and old radiators often require higher flow temperatures. Both factors reduce efficiency. Nevertheless, a heat pump can still be a sensible option, as even an unrenovated building can often be made suitable for the use of a low-temperature heat generator with just a few minor measures. In many cases, simply replacing individual radiators is sufficient. Individual consultation is recommended.
Buy a KERMI heat pump
We attach great importance to the highest quality and flawless installation of our products. That is why we sell KERMI heat pumps exclusively via the three-stage sales channel. This ensures that you not only receive a premium product, but also benefit from the best possible advice, planning and professional installation. Your qualified local specialist partner is your direct contact and ensures the optimal integration of our efficient and sustainable heating solutions into your home.