Domestic Annual Heat Pump System Efficiency (DAHPSE) - Estimator - BETA


A heat pump can be used in dwellings for space and/or hot water heating.

Heat pumps may cause fewer CO2 emissions than other types of domestic space and hot water heating systems when appropriately designed and installed.

The purpose of this website is to provide annual performance estimates for electrically-driven heat pumps installed in UK homes and enable comparison of products and installation scenarios.

Heat pump basics

A heat pump is a device that transfers heat energy from a heat source to a higher-temperature heat sink, typically for space or hot water heating purposes.

A heat source for a heat pump is normally provided by heat energy in the air (air source heat pump) or heat energy in the ground (ground source heat pump). Other heat sources can be used.

In the UK, a heat sink is normally a water-based system in the form of radiators, underfloor heating or fan convector radiators. These are often referred to as heat emitters.

In order to transfer or “pump” heat from a source to a sink, most heat pumps use an electrically-driven compressor.

Heat pumps operate more efficiently when the source temperature is higher (warmer days). If the sink temperature (the temperature of water flowing through emitters) can be reduced, this also increases efficiency.

The ability of a heat pump to transfer heat during very cold periods may be limited; therefore, some heat pumps incorporate a direct-electric heater to supplement space or hot water heating. This will mean more electricity is used for heating than if the heat pump itself were providing all the heat, so reduces annual performance and increases running costs and CO2 emissions.


Efficiency can be defined as:

Because energy cannot be created or destroyed, efficiency can never exceed 100%. However, because a heat pump transfers or “pumps” heat energy from heat source to heat sink, it is possible for more heat energy to be transferred than electrical energy supplied to the heat pump – the efficiency can therefore exceed 100% in this special case.

Since the above can cause confusion, "Coefficient of Performance" (COP) is used; this is simply the above equation without a "100" multiplication, i.e. a ratio such as 2.9.

The COP is an instantaneous measurement and reflects the sink and source temperatures at a particular moment, such as during a test. In practice, it is of limited use for evaluating or comparing performance throughout a year, where source temperatures (such as outside air) will change significantly. Water flow (sink) temperatures through the heat emitters may also change throughout the year, for example due to weather compensation controls.

In order to estimate annual performance, the European Union’s Ecodesign regulations utilise a test and calculation standard (EN14825:2016) at a wide range of temperature conditions. These are used to calculate a Seasonal Coefficient of Performance (SCOP) for a heat pump, which is used to derive an energy label class (A++ to G) for comparison purposes.

Unfortunately, the SCOP estimation of performance misses a number of important issues that may affect the performance of a heat pump when installed in homes. These include:

  1. Heat loss of the actual dwelling in which the heat pump is installed is ignored
  2. It uses average European climate data
  3. Hot water heating operation is ignored, including its impact on space heating operation
  4. Heating hours
  5. For inverter (modulating) heat pumps, the minimum heat output is not defined, meaning some heat pumps may cycle on/off more than others at identical temperature conditions
  6. Weather compensation is always assumed to be present

The Building Research Establishment has developed an annual efficiency calculation method that utilises the engineering standard EN15316-4-2:2017 to address these issues.

Annual efficiency (or SPF) can be defined in a number of different ways, and can include or exclude electrical energy needed for different heat pump system components. The annual efficiency estimates provided by this website include all auxiliary components necessary for operation, including back-up direct-electric heaters and circulation pump. This type of annual efficiency (or SPF) is often known as SEPEMO “SPF_H4”. The Seasonal Performance Factor (SPF) is the same as annual efficiency, but is not multiplied by 100.

Calculating annual efficiency

To estimate heat pump annual efficiency, an annual combined space and hot water heating duty cycle is used, which incorporates hourly space and hot water heat load and temperature assumptions, using average UK weather data (taken as City of Leeds). Heat pump test data satisfying Ecodesign regulation requirements (EN14825:2016) is used as an input to the calculation.

The calculation method, using UK average hourly source temperatures, provides more accurate and useful estimates of UK domestic heat pump performance than Ecodesign energy label indications. It is based on the calculation standard EN15316-4-2:2017 and tackles the issues highlighted in the above Efficiency section. In particular, the impact that dwelling heat loss and hot water heating have upon annual efficiency.

Calculated annual efficiency values are held in the Product Characteristics Database (PCDB), a publicly available database. Heat pump manufacturers apply for entry of heat pumps in the PCDB via application, whereby Ecodesign test data (EN14825:2016) is submitted for processing into annual efficiency values. These values, which can be viewed within this website, are used to support the UK’s National Calculation Methodology for energy rating of dwellings (known as SAP).