June 3, 2025, 11:17 am | Read time: 3 minutes
Heat pumps are considered a key technology on the path to climate neutrality, but many systems fall short of expectations. A recent study by ETH Zurich reveals the reasons and offers advice on how affected owners can take corrective action.
A field study by ETH Zurich examined the efficiency of over 1,000 heat pumps in Europe. The result: Many systems operate significantly below their potential—and for reasons other than initially assumed. The efficiency losses of heat pumps often go unnoticed but are avoidable, according to the researchers.
Significant Efficiency Differences in Heat Pumps
ETH Zurich analyzed the performance of more than 1,000 heat pumps in ten European countries, including Germany, Austria, and Sweden, in a two-year field study. The results were published in May 2025. The goal was to make the energy efficiency of the systems comparable, independent of building conditions or user behavior. The evaluation was based solely on physical measurements such as flow temperature and real-time electricity consumption.
“Our results can be generally interpreted because the collected data and algorithms are based solely on physical measurements like flow temperature or energy consumption,” explains Tobias Brudermüller, one of the study’s main authors.
The results reveal a sometimes drastic discrepancy in the efficiency of the systems studied. The difference between the most efficient and the least efficient systems was sometimes a factor of three. The metric for evaluating efficiency is the annual performance factor (APF). An APF of 3 means that 1 kilowatt-hour of electricity produces 3 kilowatt-hours of heat.
Incorrect Planning and Settings as Main Causes
A central issue: Many of the analyzed heat pumps are either incorrectly sized or poorly adjusted. About 17 percent of the air-source heat pumps studied did not even meet European efficiency standards. Often, simple operational or planning errors were the cause.
Almost one in ten systems was oversized—too large. As a result, they consume unnecessarily high amounts of electricity and operate inefficiently. Conversely, one percent of the systems were too small, leading to continuous operation at full capacity and, thus, premature wear.
Researchers more frequently found incorrect settings for the heating curve, heating limit, or flow temperature. As a result, systems often began heating at mild outdoor temperatures or operated with excessively high flow temperatures. These factors lead to avoidable energy loss.
“Even though we knew that faulty planning and settings in heat pumps are not uncommon, we were surprised by how much this is reflected in the actual efficiency level achieved and how clearly this is visible in the data,” explains Prof. Dr. Thorsten Staake from ETH Zurich.
Researchers’ Proposed Solution
The study proposes a standardized Europe-wide monitoring of heat pumps as a solution. This should be realized through the widespread use of smart meters—internet-enabled electricity measuring devices. The data collected with these devices could help identify weaknesses and address them through automated analyses. The goal is to create a system that alerts operators to optimization potentials.
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Practical Tips for More Efficiency in Operation
Heat pump operators can optimize their systems with simple measures. The researchers recommend the following:
- A constant and preferably low flow temperature—ideally between 35 and 55 degrees Celsius—is a clear sign of efficient operation.
- An APF above 3 indicates a good ratio between electricity used and heat generated and can usually be viewed via an app or directly on the control device.
- Consistent operation—with as few on and off cycles as possible—is an indicator of a well-tuned system.
Technology Is Not the Problem
“The Fraunhofer Institute for Solar Energy Systems (ISE) has also researched the efficiency of heat pumps. The result: With the use of artificial intelligence, heat pumps would run much more efficiently. The Swiss study once again shows that the real issue is not the technology itself but its practical application. With proper planning, sizing, and control, the efficiency of many systems could be significantly increased.”