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Energy Calculation

Our energy calculator helps you to identify how much energy is used to heat your water to the desired temperature. Saving water can reduce energy in the home, as 25 % of consumer energy bills is linked to heating hot water.

The methodology we use is based on agreed temperatures taken from recognised product standards.


To calculate, consistently, the energy used to heat water, average supply and delivery temperatures along with average use patterns have to be established. The basic calculation is based on first principle physics:-

Energy [kWh] = Mass [kg] x spec. Heat-coefficient of water [kWh (kg x K)] x Delta T [T]

This basic calculation coupled with average use times can easily be used to calculate expected annual energy consumption.

Average use times to be used for the following products are:-

  • Basin and Bidet taps to 7 events per person per day – 1 minute per event

  • Kitchen taps to 7 events per person per day – 1 minute per event

  • Showers (handsets & mixer controls): 7 minutes per event, 1 event per person per day

Electric Shower Flow Rate Calculation

For basin & bidet taps and showers, the average outlet temperature is always regarded as 38°C while for kitchen taps the average outlet temperature is regarded at 45°C. In all cases, the average seasonally adjusted inlet temperature is regarded as 15°C.

Core assumptions have been taken directly from the European Commission study into taps and showers task 3 report: users. For reference purposes, this document can be found via this link.

For Baths, the same core calculation can be used to help users understand, in energy terms the cost of filling the bath for each bathing event.

The energy icon can be added to the base of the Water Label to depict to the consumer the expected annual energy cost of using the product. It is required that all basin taps, kitchen taps, showers (handsets and mixer controls) and baths shall carry the energy icon.

Energy Calculator for Showers
Energy Calculator for Basin Taps
Energy Calculator for Basin Taps with Cold Start
Energy Calculator for Kitchen Taps