A short answer, followed by the source guide and related questions.
Heating 1 m³ of water through 50 °C requires about 58 kWh of useful heat before system losses. Fuel use and emissions then depend on the actual heat source, efficiency and reporting factor.
This answer is taken from Industrial Water Efficiency Assessment. Use the full guide for scope, assumptions and cited sources.
Use measured surface area, temperature and operating hours to calculate heat loss from boilers, kilns, heat exchangers, valves and pipework. Inzonex supplies removable modular insulation for equipment that requires maintenance access.
Do not add a calculated reduction to an emissions report until the reporting boundary, factor, implementation date and verification method have been approved.