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How is usage data calculated?

How Homely estimates energy used for heating and hot water

Most heat pumps do not provide a direct measurement of how much electricity they use for heating and hot water. Instead, Homely estimates this value using information reported by your heat pump, together with performance data provided by the manufacturer.

These estimates help you understand how your heating system is performing and how much energy it is likely to be using.

How does Homely calculate energy use?

To estimate electricity consumption, Homely calculates:

  • How much heat your heat pump is delivering to your home.
  • How efficiently your heat pump is operating at that moment, known as its Coefficient of Performance (CoP).

Estimating heat delivered

Your heat pump continuously measures:

  • The temperature of the water leaving the heat pump (flow temperature).
  • The temperature of the water returning to the heat pump (return temperature).
  • The flow rate of water through your heating system.

By combining these measurements, Homely can estimate how much heat is being transferred into your radiators, underfloor heating, or hot water cylinder.

For example, if water leaves the heat pump at 50°C and returns at 45°C, the water has transferred some of its heat into your home. Using the flow rate and temperature difference, Homely can estimate the amount of heat being delivered.

Understanding CoP

The Coefficient of Performance (CoP) measures how efficiently a heat pump converts electricity into heat.

For example:

  • A CoP of 3 means that for every 1 kWh of electricity used, the heat pump produces approximately 3 kWh of heat.

Heat pump manufacturers publish performance data showing the expected CoP under different operating conditions, such as outdoor temperature and flow temperature. You can see an example here:

Screenshot 2026-04-28 174011

Because real-world conditions rarely match these published values exactly, Homely estimates the most appropriate CoP by using the nearest available manufacturer data.

Estimating electricity consumption

Once Homely has estimated both the heat being delivered and the heat pump’s efficiency, it can estimate how much electricity is required to produce that heat.

For example, if:

  • Heat delivered = 7 kW
  • CoP = 3

Homely estimates that the heat pump is using approximately 2.3 kW of electricity while delivering 7 kW of heat.

A note on accuracy

The energy figures shown in Homely are estimates rather than direct measurements. They are calculated using temperatures and flow rates reported by your heat pump, combined with manufacturer performance data.

While this approach provides a good indication of system performance and energy consumption, actual electricity usage may vary slightly from the values shown. Factors such as installation design, system maintenance, weather conditions, and heat pump operation can all affect real-world performance.