Heat Pumps in Multi-Family Buildings: Why Missing Data Decides Cost and Efficiency
In most heat pump projects for multi-family buildings, the data that will later decide efficiency and cost is missing before the tender ever goes out: load profiles, temperature curves, fault histories and the exact location of meters and sensors. Without this information, planners work with rough estimates that often have little to do with how the building actually runs, and that almost inevitably leads to incorrect system sizing.
For housing companies, this is more than a technical detail. Converting your first multi-family building to a heat pump also sets the data standard that every other building in your portfolio will be measured against.
Four data gaps most often decide whether such a project succeeds:
- Without real load profiles and temperature curves, planners often size the heat pump too large or too small.
- Without documented fault histories, it stays unclear whether the old system fails for structural or hydraulic reasons.
- Without a reliable picture of meters and sensors, consumption-based billing is difficult to implement cleanly.
- Without a prioritization framework for the portfolio, housing companies often end up starting with exactly the wrong building first.
What Operating Data Is Missing Before Heat Pump Planning in Multi-Family Buildings?
Before planning starts, seven key data fields are typically missing in practice, ranging from load profiles to the meter and sensor situation in the building. Each one influences how large the heat pump ends up being sized and how realistic the later economic calculation turns out.
- Load profiles: quarter-hourly or hourly heat and electricity load over at least one full heating season.
- Temperature curves: supply and return temperatures per riser across different seasons.
- Runtimes: operating hours, cycling frequency and downtime of the existing heat generators.
- Fault histories: documented failures, error messages and repairs from recent years.
- Hydraulic irregularities: known imbalances between risers, cold apartments, unusual return values.
- Consumption patterns: actual annual consumption for heat, hot water and auxiliary electricity per meter.
- Meter and sensor situation: existing measuring points, their communication capability and data access.
The last two points are the ones most often underestimated. Whether the existing system data is actually usable, or simply sits unused in the basement, depends on how connectable the existing heating system is, in other words, which meters can be read remotely and which sensors are missing altogether. How available system data and connectivity actually come together in practice usually only becomes clear once you carry out a detailed inventory.
What System Data Needs to Be Solid Before the Tender Goes Out?
Before any tender, you need at least a room-by-room heat load calculation under DIN EN 12831 and a completed hydraulic balancing. Since 1 October 2024, this has been a legal requirement under Section 60c of the German Buildings Energy Act (GEG) for every newly installed water-based heating system in buildings with six or more residential units, using what is known as Method B, the premium procedure. For existing systems, the deadline to complete this runs until 30 September 2027.
The problem: this groundwork is simply missing in many existing buildings. Tenders then start from flat-rate assumptions, which makes the later system sizing vulnerable right from the start.
Good to know: according to estimates by co2online, around two-thirds of heating systems in the German building stock still have not been hydraulically balanced. If you put a heat pump out to tender without closing this gap first, you simply shift the problem into the bidding phase.
Which Figures Only Become Visible During Pilot or Trial Operation of the Heat Pump?
Some figures simply cannot be calculated in advance. They only become visible once the system is actually running, above all the real seasonal performance factor (the ratio of heat delivered to electricity used over a full year). Field measurements by Fraunhofer ISE on 77 heat pump systems in existing buildings show an average seasonal performance factor of 3.4 for air-to-water systems and 4.3 for ground-coupled systems, with no measurable link between a building's construction year and its actual efficiency.
A Fraunhofer IBP study of 37 model projects with heat pump heating capacities between 7 and 120 kilowatts confirms this picture even more clearly. Almost all systems still showed significant room for improvement once running, and some had to be completely replaced within their very first year of measurement. Without a trial period with real measurement, weaknesses like these stay hidden until the next heating season.
How Do Missing Data Distort Heat Pump Sizing and Economics?
Missing operating data distorts sizing in two directions at once. Systems end up oversized and unnecessarily expensive, or undersized and unable to cover the heat load on cold days. According to Fraunhofer IBP, elevated system temperatures used to prevent Legionella and poorly balanced hydraulics are among the main causes of low seasonal performance factors in multi-family building operation.
An analysis of field measurement data by energieverbraucher.de shows just how significant this effect is:
| System | Supply Temperature | Heating System | Seasonal Performance Factor |
|---|---|---|---|
| Poorly balanced | approx. 54°C | Radiator heating | 1.8 |
| Correctly set | approx. 40°C | Radiator heating, no underfloor heating | 3.7 |
A correctly balanced system reaches more than double the efficiency of the very same radiators, purely through a lower supply temperature. Without documented temperature curves, this difference is impossible to spot before the tender.
Common misconception: practical experience from the installation industry shows that in around 80 to 90 percent of reported faults, peripheral equipment or installation errors in the surrounding system turn out to be the actual cause. The heat pump itself is rarely the defective part. Without a fault history, this distinction gets missed regularly during troubleshooting.
The grid situation is another factor that's easily forgotten. Since 1 January 2024, every newly installed heat pump has to be registered with the electricity grid operator, who then has eight weeks to carry out a grid compatibility check. If overload is a risk, output can be throttled down to a guaranteed minimum of 4.2 kilowatts. If you don't clarify this in advance, you tend to find out right in the middle of construction. Basing operating decisions on real operating data helps you avoid surprises like this later in the project.
How Should Housing Companies Prioritize Their Portfolio for the Switch to Heat Pumps?
Rather than converting the entire portfolio at once, housing companies should first identify the buildings where data availability, heat load and renovation status line up. The pressure behind this is real: the energy renovation rate across the German residential building stock currently sits at only around 0.67 percent per year, while the 2030 climate targets would require at least 2 percent.
The sheer number of affected residential units adds even more pressure to get prioritization right. According to Deutsche Umwelthilfe, more than half of Germany's 42.8 million residential units sit in multi-family buildings, where heat pumps remain rare and fossil heating systems still dominate. A housing company that tackles every building at once ties up planning capacity without actually speeding up solid results.
A more realistic approach shows up in LEG Immobilien's portfolio. There, around 500 heating systems are being decarbonized step by step by adding heat pumps alongside gas boilers, with the heat pumps taking over most of the heat supply, a shift that saves roughly 13,000 tonnes of CO₂ per year. Construction year matters less for sequencing. What matters more is which building already delivers usable operating data, as prioritization in a decarbonization context shows. The pace of decarbonization often depends more on which building you tackle first than on the system technology itself.
What Monitoring Structure Keeps the Heat Pump Running Well After Commissioning?
Once the system is up and running, only continuous remote monitoring with automated checks on key operating parameters ensures the heat pump actually reaches its efficiency potential. That is exactly what Fraunhofer ISE recommends after four years of field research in the "WP-QS im Bestand" project, with a clear pointer to build the monitoring concept into planning early on, well before commissioning.
Alongside the Fraunhofer recommendation, a new legal requirement now applies. Since 1 October 2024, the heat pump exemption in the German Heating Costs Ordinance (Heizkostenverordnung) no longer applies. Heating costs in multi-family buildings with a central heat pump must now be recorded on a consumption basis through separate electricity and heat meters, and the transition period for retrofitting this metering equipment ended on 30 September 2025. Anyone planning today needs this meter infrastructure anyway, and it is exactly what makes monitoring possible in the first place.
This is exactly the point where it pays to make operations digitally visible. A platform like KUGU VIS (Visuelles-Informationssystem) makes system data, temperature curves and irregularities visible before and after rollout, while KUGU EOS (Energie-Optimierungssystem) automatically adapts day-to-day operation to the real load profile. That way, the heat pump doesn't stay frozen at its commissioning-day efficiency level, but keeps developing alongside actual consumption data.
Why Data Readiness Decides Heat Pump Success in Existing Buildings
The real obstacle to the heat transition in multi-family buildings rarely sits in the system technology itself. It sits in the gap between what planners would need for a tender and what housing companies can actually provide. This gap is one of the reasons the renovation rate is still stuck at 0.67 percent, while the number of multi-family buildings running on outdated fossil systems stays enormous.
For housing companies, this means something concrete: the first step is a data check on the first pilot building, covering load profiles, temperature curves, fault history and meter locations. That foundation is what makes a genuine comparison possible between which building in the portfolio comes next. It is also what makes the economic calculation hold up once the system is actually running.
FAQ: Common Questions About Data and Heat Pumps in Multi-Family Buildings
How Long Does the Grid Compatibility Check Take for a Heat Pump in a Multi-Family Building?
The electricity grid operator has a maximum of eight weeks after registration to complete the grid compatibility check. This registration requirement has applied since 1 January 2024 to every newly installed heat pump with an electrical output of 4.2 kilowatts or more. If grid overload is a risk, output can be temporarily throttled down to this minimum level.
From How Many Residential Units Does Hydraul1ic Balancing Become Mandatory?
From six residential units upward, hydraulic balancing has been a legal requirement since 1 October 2024, as soon as a new water-based heating system gets installed. It's based on a room-by-room heat load calculation under DIN EN 12831 using the premium procedure. For existing systems, the compliance deadline still runs until 30 September 2027.
Does a Building's Construction Year Affect Heat Pump Efficiency?
No, field measurements by Fraunhofer ISE on 77 systems found no measurable link between a building's construction year and the seasonal performance factor achieved. What mattered more was the actual hydraulic balancing and the system temperatures being run. An older building can therefore run just as efficiently as a new one, provided the system is set up correctly.
Does Heat Pump Electricity in Multi-Family Buildings Have to Be Billed Separately?
Since the heat pump exemption in the Heizkostenverordnung ended on 1 October 2024, billing in multi-family buildings has run on a consumption basis through separate electricity and heat meters. For existing systems, a transition period allowed retrofitting of this metering equipment until 30 September 2025. Without these meters, legally sound billing is barely possible anymore.
What Are the Signs That a Heat Pump System Is Running Below Its Potential?
Three signals tend to show up together. Supply temperatures on radiators stay persistently above 50 degrees, fault alerts keep appearing without an actual defect in the heat pump itself, and there's a noticeable gap between the projected and the actually measured seasonal performance factor. Fraunhofer field studies show that almost every existing system examined still had measurable room for improvement once running.
