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Published on: February 19, 2026 / Updated on: February 19, 2026 – Author: Konrad Wolfenstein
From oil boiler to heat pump: A practical report and worthwhile path to the private energy transition – Creative image: Konrad Wolfenstein
Anyone working in the renewable energy sector is familiar with the large-scale projects: wind farms, industrial-scale solar fields, and grid infrastructure for the energy transition. The processes are well-established, the general contractors are known, and the procedures are standardized. But as soon as it comes to one's own single-family home, the adventure begins anew. Although I deal with renewable energy on a daily basis, these are exclusively large-scale industrial projects. I lacked any experience in the private customer sector and had to rely on service providers I was completely unfamiliar with. The market for private homeowners operates according to its own rules: fragmented, opaque, dominated by local tradespeople, and with a subsidy landscape that, while generous, is bureaucratically complex. This experience is the focus of this report, which also provides an economic analysis of the German heat pump market.
This article was written entirely privately and on my own initiative – without any consultation with the companies mentioned. It is intended as a personal thank you for the excellent work and the smooth process.
The decision to replace an existing oil heating system with a heat pump today follows a clear economic logic. An already installed photovoltaic system on the roof provided the decisive impetus: Until now, the self-generated electricity could either be fed into the grid or used in the household. However, the decreasing feed-in tariff coupled with rising electricity prices is making self-consumption increasingly attractive. In this scenario, a heat pump is the ideal large-scale energy consumer in the household. It increases the self-consumption rate from the typical 20 to 30 percent to 50 to 60 percent when an intelligent energy management system coordinates the heat pump's operating times with the peak generation of the solar system.
The economic calculation works even without existing photovoltaics: The total operating costs of a heat pump are €8,000 to €15,000 lower than those of a gas condensing boiler over a 20-year period, provided all available subsidies are utilized. The ecological benefit, a CO2 reduction of three to five tons per year, is an additional societal advantage.
During my online research for a suitable service provider, I came across Enovato GmbH, which operates under the brand name 42WATT and collaborates with the trades company WAV Solar. Behind this business model is a concept that is increasingly transforming the traditional heating industry: a digital energy consulting platform that connects homeowners with regional tradespeople. The company name 42WATT refers to the goal of reducing energy consumption in German buildings to below 42 kilowatt-hours per square meter per year in order to achieve climate neutrality. The platform handles consulting, planning, grant applications, and long-term support, while the actual installation is carried out by local master craftsmen from a network of over 100 regional partners.
The Munich-based clean-tech company was financed in a seed round with the participation of prominent investors and developed its algorithm in collaboration with the Technical University of Munich. This algorithm uses ten data points, such as electricity consumption and year of construction, to create a 3D model of the house and simulate energy potentials like heating load and photovoltaic coverage. At the end of January 2026, OBI Group Holding acquired a majority stake in Enovato GmbH, granting access to more than 350 OBI stores in Germany and making the model scalable nationwide.
This platform model addresses a structural problem in the German skilled trades: In the plumbing, heating, and air conditioning sector alone, there was a shortage of over 12,000 skilled workers in March 2025, and every second position remained unfilled. The industry association estimates the gap at up to 60,000 missing heating installers overall. Those who contact individual tradespeople directly often encounter waiting times of several months. A platform provider with an established partner network can assign jobs more quickly and plan professionally in advance, which benefits both homeowners and tradespeople.
From the outset, communication with 42WATT was excellent. The consultation was independent and manufacturer-independent, which is a key differentiator of this provider: they don't sell a specific product, but rather develop the optimal solution for each individual building. A certified energy efficiency expert prepared the plan, which included a room-by-room heating load calculation according to DIN 12831. This calculation, in the form of the so-called Procedure B, has been mandatory since January 1, 2023, for receiving funding through the federal government's subsidy program for efficient buildings. Procedure B is significantly more precise than the previously permitted Procedure A, as it takes into account the actual structural characteristics of each individual room and derives the necessary system temperatures and water volumes from them.
Based on this calculation, hydraulic balancing was carried out, ensuring that each radiator and each heating circuit in the building receives precisely the correct amount of hot water. Without this balancing, some rooms would be oversupplied and others undersupplied. Studies estimate the energy savings potential of a correctly performed hydraulic balancing at up to 15 percent.
The chosen system is a state-of-the-art monobloc air-to-water heat pump. In a monobloc design, all central components, including the refrigerant circuit, are located in the outdoor unit, which significantly simplifies installation and eliminates the need for F-gas certification for the installer. The system uses the natural refrigerant R290, propane, which has a particularly low global warming potential and allows for higher flow temperatures than synthetic refrigerants. Flow temperatures of up to 75 degrees Celsius make the system suitable even for existing buildings with conventional radiators, a key advantage when modernizing older homes.
The outdoor unit achieves a maximum heating output of just under 7 kilowatts and is therefore designed for the typical heating requirements of a well-insulated detached house. Inside the house, a hydraulic station with an electric auxiliary heater has been installed to cover peak loads during extremely low outdoor temperatures. A 100-liter buffer tank serves as a heat buffer for the underfloor heating, while a separate 300-liter hot water storage tank handles domestic hot water heating.
Before the new technology could be installed, the old oil heating system had to be dismantled. This process is by no means trivial, as it touches upon numerous legal areas: waste management law, occupational safety law, building law, soil protection law, hazardous substances law, and water law. Heating oil is classified as significantly hazardous to water under the Ordinance on Installations for Handling Substances Hazardous to Water, which is why its disposal may only be carried out by certified specialist companies in accordance with Section 62 of the Federal Water Act.
In this specific case, the dismantling included decommissioning and proper disposal of the oil heating system, the old hot water and buffer storage tanks, and a steel oil tank. At the customer's request, the remaining oil was pumped to another tank at a nearby address for further use. Additionally, a brick protective wall in the oil tank room had to be demolished to make room for the new equipment. The removal of bushes and small trees at the planned installation site for the outdoor unit was also part of the scope of work.
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The core of this technological advancement is the deliberate departure from conventional clamp mounting, which has been the standard for decades. The new, more time- and cost-effective mounting system addresses this with a fundamentally different, more intelligent concept. Instead of clamping the modules at specific points, they are inserted into a continuous, specially shaped support rail and held securely in place. This design ensures that all forces – whether static loads from snow or dynamic loads from wind – are distributed evenly across the entire length of the module frame.
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The actual installation by the regional partner company WAV Solar included mounting the outdoor unit on a specially constructed strip foundation with excavation work, laying frost-proof pipes with 200 percent insulation in the exterior area in accordance with the German Building Energy Act (GEG), core drilling for the building entry point, connection to the existing heating system, and complete electrical wiring. The heating circuits were flushed with softened water according to VDI 2035 to prevent limescale deposits and corrosion in the system. Finally, commissioning and training were carried out.
The tradespeople on site carried out the work with a high degree of professionalism and remarkable courtesy. They even took off their shoes before entering the house, which was immediately clarified as unnecessary. However, the installers did not speak German, which made direct communication on the construction site difficult. Nevertheless, it was always possible to contact the German-speaking colleagues at 42WATT by phone if questions or problems arose, although some patience was required as not every contact person was immediately available.
This situation points to a structural reality of the German skilled trades market. The massive shortage of skilled workers in plumbing, heating, and air conditioning means that businesses are increasingly reliant on foreign skilled workers. As early as 2023, the German government, in response to a parliamentary inquiry, explicitly referred to skilled worker immigration as a fundamental solution to the plumbing and heating shortage. The German Confederation of Skilled Crafts emphasizes that foreign skilled workers are indispensable for keeping the skilled trades operational. From a pragmatic perspective, the language skills of an individual installer have no bearing on the quality of the workmanship, which in this case was impeccable. Anyone who wants to receive quality and top-notch service in the skilled trades in Germany today must accept the realities of the market, be patient, express their questions clearly and objectively, and will then receive top-quality service in return.
With its federal funding program for energy-efficient buildings, the government has created a support structure that significantly simplifies heating system replacements for private individuals. The central instrument is the KfW program 458, which is specifically tailored to replacing fossil fuel heating systems. The funding consists of a basic grant and several combinable bonus components: a climate speed bonus for the rapid replacement of old oil or gas heating systems, an income bonus for lower-income households, and an efficiency bonus for particularly environmentally friendly heat pumps, such as those using natural refrigerants. In total, grants of up to 70 percent of eligible costs are available, with a cap on the grant amount per residential unit.
As part of the overall package, 42WATT handled the complete application process: from preparing the required confirmation of eligibility, which is a prerequisite for submitting the application to KfW, to assisting with the application itself, and finally, providing confirmation after completion and submitting all necessary documentation. This comprehensive, one-stop service is a significant advantage over the traditional approach, where homeowners largely have to navigate KfW's bureaucratic requirements on their own.
The entire process took place in a highly dynamic market environment. After the record year of 2023, with 356,000 heat pumps sold, the market collapsed by 46 percent in 2024 to just 193,000 units. Sales of air-to-water heat pumps, by far the dominant technology, fell to around 178,000 units. The German Heat Pump Association (BWP) attributed this to political uncertainty among consumers, triggered by the heated debate surrounding the Building Energy Act and the announcement by the then-federal government that it intended to repeal the Heating Act in its original form.
A recovery only became apparent in the first quarter of 2025: Sales rose by 35 percent to 62,000 units, and the industry projected around 260,000 heat pumps for the entire year. Germany is thus still far from its politically stated goal of installing 500,000 heat pumps annually and having six million units in operation by 2030. At the end of 2024, there were only around 1.8 million heat pumps in operation.
What's remarkable is what begins after installation. Free remote maintenance and efficiency analysis are included for the first year, as is digital system monitoring. After the first year of operation, a free fine-tuning is provided to optimize the system based on actual consumption data. Regular maintenance according to manufacturer specifications is organized by 42WATT and is a prerequisite for the five-year manufacturer's warranty.
This service model differs significantly from traditional heating system installation, where contact with the installer often ceases after handover. Existing customers of the provider report that even months after installation, there is a lively exchange regarding settings, remote maintenance systems, and further optimizations. In a market where the heat pump not only needs to be installed but also operated and fine-tuned for years, this form of long-term support is a genuine competitive advantage. The payment terms are standard for the industry and customer-friendly: a partial down payment before installation, with the majority due only after commissioning and completion of all work.
The described process exemplifies how the energy transition in private buildings works in practice and where its challenges lie. The technology is mature: Modern monobloc heat pumps with natural refrigerants achieve efficiency levels that were unthinkable just a few years ago, and combining them with an existing photovoltaic system raises the overall energy performance of the building to a new level. The available subsidies are generous enough to largely offset the cost disadvantage compared to fossil fuel systems.
The bottlenecks lie elsewhere: in the shortage of skilled workers, which is slowing down installations; in the political uncertainty, which is making consumers hesitant; and in a societal debate that gets bogged down in side issues like the language skills of installers, instead of focusing on the results. Platform models like that of Enovato GmbH, which, together with 42WATT and regional partners like WAV Solar, offers the entire process from consultation to long-term system maintenance from a single source, provide a compelling answer to market fragmentation. Those who choose this path are making an economically and ecologically sound decision that can be quantified in hard numbers: lower operating costs, greater independence from fossil fuels, and a building that is equipped to meet the regulatory requirements of the coming decades.
Konrad Wolfenstein
I and my team are happy to be available to you as your personal advisor.
You can contact me by filling out the contact form here or simply call me at +49 89 89 674 804 ( Munich) . My email address is: [email protected]
I'm looking forward to our joint project.
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© February 2026 Xpert.Digital / Xpert.Plus – Konrad Wolfenstein – Business Development
