Resistive heating is considered to be 100% energy efficient in heat conversion when measured on a watt-per-watt basis.
That's to be expected as they are essentially entropy production systems.
However, heat pumps are more than 100% efficient on a watt-per-watt basis as they are not directly converting electricity into heat, but rather are moving heat from one area to another.
Heat pumps currently are between 150% to 400% efficient on a watt-per-watt basis, which could mean that your ideal hot water heater could run on as little as 240v/10a, or 120v/18a (120v/20a breakers are common in kitchens, to power microwaves and refrigerators, so this wouldn't be a huge stretch for a hot water system, either).
Additionally, the state of the art is always improving.
Recent heat pump advancements have been made with CO2 for use in electric vehicles that may push past the 400% efficiency rating, which could make it even lower than that.
> However, heat pumps are more than 100% efficient on a watt-per-watt basis as they are not directly converting electricity into heat, but rather are moving heat from one area to another.
To reactivate this dead thread: I thought of that, but I don't think it's an argument in favour of on-demand electric heating. A heat pump capable of delivering ~16kW of heat equivalent on demand would be something like 50,000BTU/hr, or larger than many whole-home air conditioning systems.
Instead, a heat pump hot water heater would be far more appropriately sized to work with a high duty cycle at lower intensity – a hot water tank.
Resistive heating is considered to be 100% energy efficient in heat conversion when measured on a watt-per-watt basis.
That's to be expected as they are essentially entropy production systems.
However, heat pumps are more than 100% efficient on a watt-per-watt basis as they are not directly converting electricity into heat, but rather are moving heat from one area to another.
Heat pumps currently are between 150% to 400% efficient on a watt-per-watt basis, which could mean that your ideal hot water heater could run on as little as 240v/10a, or 120v/18a (120v/20a breakers are common in kitchens, to power microwaves and refrigerators, so this wouldn't be a huge stretch for a hot water system, either).
Additionally, the state of the art is always improving.
Recent heat pump advancements have been made with CO2 for use in electric vehicles that may push past the 400% efficiency rating, which could make it even lower than that.