Water heating

Three propane water heaters.

Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning and bathing, and space heating. In industry both hot water and water heated to steam have many uses.

The most common energy sources for heating water are fossil fuels: natural gas, liquefied petroleum gas, oil or sometimes solid fuels (coal or firewood. These fuels may be consumed directly or by the use of electricity (which may derive from any of the above fuels or from nuclear or renewable sources). Alternative energy such as solar energy, heat pumps, hot water heat recycling, and sometimes geothermal power, may also be used as available, usually in combination with gas, oil or electricity.

Solar water heaters

Direct-gain solar heater panels with integral storage tank installed near a house in the Cirque de Mafate in Réunion

Solar collectors for solar powered water heaters are installed outside dwellings, typically on the roof or nearby. Nearly all models are the direct-gain type. They consist of flat panels in which water circulates.

Geothermal heating

In countries like Iceland and New Zealand, and other volcanic regions, water heating may be done using geothermal power, rather than combustion.^[1]

Water Heating Media

1. Municipal water feed
2. Fluid from water storage tank to external (passive) heat source; passive heat source can be the ground (soil or groundwater), sun or air via heat pump, district heating or thermodynamic solar panel
3. Fluid from heat pump, or thermodynamic solar panel to water storage tank
4. Pump, actuator, controller and other parts
5. Water heater
6. Water storage tank
7. Hot water to domestic appliances
A small hot water heater repair in Fresno white color
Electric-tank–type storage water heater (US)
Gas furnace (top) and storage water heater (bottom) (Germany)
The inside of a hydraulically operated two-stage tankless heater, heated by single phase electric power. The copper tank contains heating elements with 7.2 kW maximum power.
An example of a poorly installed electric shower head in Guatemala.
1500W Immersion heater with sheathed element, designed to be immersed in a small vessel such as a carafe or bucket. Since it does not detect the presence of a liquid, it can become very hot if run dry, posing a hazard.
Flat-plate solar thermal collector, viewed from roof-level
Display of water heaters used in the past