SCOP and ETAs
This is how a heat pump's energy efficiency class is determined
Two key figures show how much electricity a heat pump uses over the course of a year to provide the same heating capacity—and how this determines its energy efficiency rating, ranging from A+++ to G.
Two abbreviations, one and the same fundamental question
Every heat pump data sheet lists several efficiency metrics side by side: COP, SCOP, ETAs, and an energy efficiency class ranging from A+++ to G. All four are related but answer different questions. The COP describes a single operating point, such as at an outdoor temperature of 7 °C. The SCOP takes the entire heating season into account. The ETAs value (ηs) converts the SCOP into the metric used for the EU energy label. Finally, the energy efficiency class is the classification of this ETAs value into one of the levels ranging from A+++ to G.
If you want to read a data sheet correctly, you can’t ignore these four terms. The following section goes through them one by one.
COP, SCOP, and JAZ: three metrics, three time periods
The COP (Coefficient of Performance) indicates the ratio of heat output to electrical power consumption at a fixed outdoor temperature and a fixed flow temperature—a snapshot value. Since a heat pump operates at a wide range of outdoor temperatures throughout a heating season, a single COP value says little about how much electricity the unit actually consumes over the course of a year.
Many data sheets list not only the COP but also the EER (Energy Efficiency Ratio): the theoretical equivalent for cooling mode, also expressed as the ratio of cooling capacity to electrical power consumption at a fixed operating point. Since a heat pump must bridge the temperature difference in the opposite direction during cooling, the EER of a unit is, for thermodynamic reasons, generally lower than the COP of the same unit in heating mode at comparable temperatures.
The SCOP (Seasonal Coefficient of Performance) applies the COP concept to an entire heating season: It describes the ratio of heat output to electrical energy consumption over the season, calculated in accordance with the European standard EN 14825. The SCOP is therefore a calculated value obtained under standardized test conditions, not a measurement taken on an actual building.
The annual performance factor (APF, sometimes also called SPF) differs from COP and SCOP in two respects . First , the system boundary: COP and SCOP consider only the heat pump’s refrigeration cycle—that is, the compressor, condenser, expansion valve, and evaporator. The JAZ, colloquially speaking, includes the entire plant in the building—such as heating circulation pumps, buffer tanks, Controller, and any supplementary electric heating—and is measured over the course of a year using the plant as it is actually installed. Second, the context: SCOP and JAZ compare energy quantities over a period of time (kWh of heat to kWh of electricity), whereas COP, as an instantaneous value, originally compares power ratings (kW to kW)—although SCOP can also be derived mathematically from integrated power values. The precise technical distinction is more nuanced here than this simplified comparison suggests; in practice, when comparing two data sheets, it is usually sufficient to keep the system boundaries and building-specific factors in mind.
How SCOP Is Calculated
The calculation according to EN 14825 follows the so-called bin method: The range of possible outdoor temperatures is divided into individual intervals (“bins”); for each interval, the heat pump’s COP at partial load is determined and weighted by the number of hours that this temperature statistically occurs during a defined reference heating season. The sum of these weighted values yields the SCOP for an entire season.
To ensure that manufacturers provide comparable values across Europe, the standard defines three reference climate zones, each represented by a city with a typical temperature profile:
C = Colder
Reference location: Helsinki. Lower design temperature, longer heating season.
A = Average
Reference location: Strasbourg. This is used as the basis for most data sheet specifications in Central Europe.
W = Warmer
Reference location: Athens. Shorter heating season, higher design temperature.
Important for comparison:
A SCOP value is only comparable to another if both were determined under the same climate zone and the same flow temperature. Data sheets therefore usually include additional information specifying the climate zone (often “average”) and the flow temperature (often 35 °C or 55 °C) for which the stated value applies.
From SCOP to ETAs: The Conversion for the Energy Label
The EU energy label does not display the SCOP itself, but rather the seasonal space heating efficiency (ETA), referred to as ηs in the standard text. It is derived from the SCOP, in part by dividing it by a specified conversion factor (CC = 2.5). This factor reflects the fact that, for electricity generation in Europe’s power plant fleet, a calculated efficiency of approximately 40 percent is assumed—this allows for a comparison between electric heat pumps and fuel-fired boilers on the same scale. Additional adjustments are factored into the final calculation, such as a contribution for the control technology used and a deduction for the energy consumption of auxiliary components like sump heating or standby operation. The exact amount of these adjustments is specified in the underlying EU regulation and varies depending on the type of appliance.
ηs ≈ SCOP ÷ 2.5 × 100%
An Overview of Energy Efficiency Classes
Since September 26, 2019, the following classification of the ETA value (ηs) into efficiency classes has applied to space heaters in the EU:
| Class | ETAs (ηs) |
|---|---|
| A+++ | ηs ≥ 150% |
| A++ | 125% ≤ ηs < 150% |
| A+ | 98% ≤ ηs < 125% |
| A | 90% ≤ ηs < 98% |
| B | 82% ≤ ηs < 90% |
| C | 75% ≤ ηs < 82% |
| D | 36% ≤ ηs < 75% |
| E | 34% ≤ ηs < 36% |
| F | 30% ≤ ηs < 34% |
| G | <: 30% |
To put this in perspective: Due to its design, an electric resistance heater has a COP of around 1, which mathematically places it in Class D. Due to their operating principle—they transfer heat from the environment rather than generating it through conversion—heat pumps achieve SCOP values well above 3 in most applications, which typically places them in the A+ to A+++ range. Where a specific model actually falls depends on the unit, the supply water temperature, and the applicable climate zone, and can be found in the respective data sheet.
Why 35 °C and 55 °C Do Not Yield the Same Result
In data sheets, SCOP and ETA values usually appear twice: once for a 35 °C flow temperature and once for a 55 °C flow temperature. 35 °C represents surface heating systems such as radiant floor heating, while 55 °C represents operation with radiators. A heat pump must bridge the temperature difference between the outside air and the flow temperature—the smaller this difference, the less electrical energy is generally required to do so. That is why the SCOP at 35 °C is typically higher for the same unit than at 55 °C.
When comparing devices, it is therefore crucial that both values be compared at the same reference temperature. Otherwise, comparing “SCOP at 35 °C” with “SCOP at 55 °C” will result in a distorted picture.
What the metric means in practice
When comparing two offers, it’s worth looking at three points in the data sheet: the climate zone used, the specified flow temperature, and finally the SCOP or ETA value under these conditions. Only when these three figures match can two units be meaningfully compared.
In addition, many subsidy programs for heating system replacements require a specific minimum SCOP or JAZ value. The specific thresholds vary by program and are regularly adjusted by the subsidy agencies; they should therefore be verified directly with the relevant subsidy agency or in the current program guidelines.
A higher SCOP or ETAs value primarily means one thing: lower electricity consumption for the same amount of heating. The extent to which this affects a building’s carbon footprint also depends on the electricity mix at the specific location and cannot be quantified in a general way for all cases.
Calculation example (illustrative): For an annual heat demand of 10,000 kWh and a SCOP of 4.0, a heat pump would theoretically require 2,500 kWh of electricity. Multiplying this by the respective grid intensity yields approximately 422 kg of CO₂ in Austria (169 g/kWh) or approximately 847 kg of CO₂ in Germany (339 g/kWh). This is a rough estimate based on the electricity mix; it is not a complete carbon footprint—which would also need to take into account manufacturing, installation, and the household’s actual electricity mix, including any contractually agreed-upon sources.