Replacing an oil or gas heater with a heat pump

The newer buildings in which the heat generator is now due to be replaced are a good 20 years old. When refurbishing the current oil orgas heating,nothing stands in the way of using a heat pump. This is because energy-efficient construction was already mandatory at the time the building was erected. The building envelope is already appropriately insulated and the windows have double glazing. As a result, the inlet temperature in the heat distribution network is already significantly lower than in the older building stock and can be reduced even further if necessary. These houses often have underfloor heating – a very good “partner” for the heat pump.

If the building is older, this is not automatically an obstacle to a heat pump. More important than the year of construction is the date of the last energy-efficient refurbishment, including the framework conditions applicable at that time. In 1977 and 1978, for example, the first thermal insulation ordinance and the first heating systems ordinance came into force, the requirements of which made it possible to systematically reduce heating requirements during the oil crisis of the early 1980s. Accordingly, houses that were renovated during this period often have good prerequisites for a heat pump, even without additional insulation of the building envelope.

The less heat needs to be generated, the better. Energy-efficient refurbishment of an old building therefore makes sense in any case. The respective manufacturers of insulation, windows, doors and heat generators naturally take a different view of what should be considered first. Only on the basis of a specific individual heat requirement calculation can be discussed, whether other measures are necessary for your building before changing the heat generator. One factor that you can easily determine in advance provides a clear indication: the inlet temperature in the existing system.

Before starting any heating system refurbishment process, the heating requirements of a building should always be determined in detail. At least, the inlet temperature delivers a basic statement on the use of a heat pump. If you use radiators, you need to take a closer look at this point. A simple test at really low outdoor temperatures provides important insights: Reduce the flow temperature of your boiler to 50 °C. If this is sufficient to achieve your desired thermal comfort, the heat pump can be used. If not, the first step should be to check whether only some radiators need to be replaced with larger models. These improvements are often sufficient.

What to do if you still have a well-functioning gas or oil heating system? Until recently, this meant bivalent operation – the control system of a modern heat pump can easily integrate another heat source and, over and above, cover peak loads at low outside temperatures. But these days, everyone should take a closer look at new options: One important point is that in bivalent operation costs for gas meters, boiler maintenance and chimney sweeps remain the same. Oil and gas prices have risen to record levels in recent months, and the annually increasing CO₂ levy is gradually adding an additional cost factor – not to mention the supply situation.

On the other hand, a complete switchover is favoured by current funding models: Instead of fixed amounts, percentages of the refurbishment measure total costs are now reimbursed. Additional bonuses for the complete switchover and the exclusion of fossil fuels from the heating supply are a further incentive. This means, for example, that if you have the old oil tank removed at the same time as the oil boiler, not only the deinstallation and disposal of the oil tank are eligible for funding, but also the refurbishment of the room in which the oil tank was located. For example, the costs that the painter estimates for the design of the old storage room can be subsidised by 35 or even 40 %, just like the heat pump. Please note: If the fossil-fuelled heating system is only disposed of after several years of bivalent operation, the disposal must be carried out entirely at your own expense. Further information on the current BEG subsidy can be found in the articleRetrofitting a heat pump.

Nevertheless, the option of bivalent operation should not be completely ruled out: If, for example, energy-saving measures are planned for the building envelope in the coming years, it makes sense to match the output of a new heat pump to the planned heat requirement. Until then, the boiler can provide the additional heat required.

In order to successfully plan and implement a heating refurbishment in existing buildings, it is important to harmonise the structural situation, your comfort requirements and your financial leeway as well as the current funding options as optimally as possible. In existing buildings, it is first advisable to find out the technical framework conditions such as the specific heat requirement and the inlet temperature currently being used. In the majority of cases, this helps to clarify whether a heat pump can be installed without further ado. If it becomes apparent that further structural refurbishment measures are mandatory, a qualified energy consultant should be called in.