+Water heater

Intro

These come in multiple forms - immersion coils, geysers.
Geysers save power and are more convenient as they’re equipped with a thermostat.
With immersion coils, there is the risk of electric shock.
“Instant” geysers are high powered and heat fast, but have low storage capacity. They are meant to drained slowly. (4.5kw 3L was insufficient for comfortable showering.)
Storage geysers heat more slowly, but can be drained a lot more (20L?) at a time. Typical storage capacity - 15 - 25 L. (20L 2kW was used by 6 people in v-nilaya BLR in 2020. Heating time 15/20 min.)

Aka reverse-cycle air conditioners.
General principles described in heat pump page.
The heating efficiency of electric water heater is less than 100%, while that of air source heat pump water heater can reach 400% when the ambient temperature is high enough. This is because heat is transferred, rather than generated using electricity. Even under 0℃ ambient temperature, the heating efficiency can be 200%, far higher than the heating efficiency of electric water heater. Thus, air source water heater can save more electricity and energy than electric water heater.
Example. At .86 kw Power: if outside temperature is 20 deg can deliver 80 deg water in 1 hour. Say if outside air is 20 degrees and max cut off set to 55 degrees, heat pump will take even lesser time.