Hot water consumption is normally a significant proportion of domestic energy consumption. The average hot water energy consumption of UK homes is approximately 4 kWh per day (based on 2.4 occupants; approx. 80 litres of hot water at 55°C). This average is based on field trial data obtained by the Energy Saving Trust, but varies significantly between homes.
The basis of heat pump annual efficiency estimates displayed by this website is that average hot water energy demands must be satisfied by the heat pump before space heating demands, with deficits satisfied by back-up direct-electric heaters. A standardised schedule for hot water consumption is used to derive these estimates, with total consumption affected by assumed dwelling heat loss.
If the hot water consumption quantity, temperature or schedule differ substantially from the assumptions used to produce annual efficiency estimates, then these estimates may be less accurate. This is particularly likely for heat pumps with a heat output less than approximately 5 kW (at -4.7°C).