IEC 60379: Household Electric Water Heater Performance — Storage vs. Instantaneous Energy Efficiency

Storage vs. Instantaneous Water Heaters — Why Efficiency Numbers Cannot Be Directly Compared

IEC 60379:1987 specifies household electric water heater performance measurement. Storage heater efficiency is dominated by standby heat loss — an 80L tank loses 1.5–2.5 kWh/day. Instantaneous heaters have zero standby loss but require very high instantaneous power (6–12 kW). IEC 60379 test conditions differ — storage measures 24h energy, instantaneous measures instantaneous efficiency — they cannot be directly compared.

TNLab — Storage and instantaneous are two completely different “hot water philosophies” — selection depends on usage patterns and electrical capacity.