Water heating

Generally the consumer has no in-building backup system as redundancy is usually significant on the district heating supply side.

In the United States, typical natural gas water heaters for households without unusual needs are 150–190 L (40–50 US gal) with a burner rated at 10.0–11.7 kilowatts (34,000–40,000 BTU/h).

Larger tanks tend to provide hot water with less temperature fluctuation at moderate flow rates.

Tiny point-of-use (POU) electric storage water heaters with capacities ranging from 8–32 L (2–6 gallons) are made for installation in kitchen and bath cabinets or on the wall above a sink.

The Coldest regions in India like Kashmir, people are mostly dependent on the storage type electric water heaters.

The main disadvantage is their much higher initial costs; a US study in Minnesota reported a 20- to 40-year payback for the tankless water heaters.

Invented in Brazil in the 1930s due to a lack of central gas distribution and used frequently since the 1940s, the electric shower is a home appliance often seen in South and Central American countries due to the higher costs of gas distribution, combined with households that in most cases do not support conventional water heaters.

In a drainback system, the water drains into a storage tank contained in conditioned or semi-conditioned space, protected from freezing temperatures.

This produces a fairly steady supply of DHW (domestic hot water) at low static pressure head but usually with a good flow.

Residential combustion water heaters manufactured since 2003 in the United States have been redesigned to resist ignition of flammable vapors and incorporate a thermal cutoff switch, per ANSI Z21.10.1.

The first feature attempts to prevent vapors from flammable liquids and gases in the vicinity of the heater from being ignited and thus causing a house fire or explosion.

These safety requirements were made in response to homeowners storing, or spilling, gasoline or other flammable liquids near their water heaters and causing fires.

Since most of the new designs incorporate some type of flame arrestor screen, they require monitoring to make sure they do not become clogged with lint or dust, reducing the availability of air for combustion.

In London, England, in 1868, Benjamin Waddy Maughan, a painter, invented the first instantaneous domestic water heater that did not use solid fuel.

The first automatic, storage tank-type gas water heater was invented around 1889 by Ruud after he immigrated to Pittsburgh, Pennsylvania (US).

The Ruud Manufacturing Company, still in existence today, made many advancements in tank-type and tankless water heater design and operation.

A standard 120V, 15-ampere rated wall electric outlet, by comparison, only sources enough power to warm a disappointingly small amount of water: about 0.17 US gal (0.64 L) per minute at 40 °C (72 °F) temperature elevation.

The energy used by an electric water heater can be reduced by as much as 18% through optimal schedule and temperature control that is based on knowledge of the usage pattern.

Under the pre-2015 standard, a 75 US gal (280 L; 62 imp gal) gas storage water heater with a nominal input of 22 kW (75,000 BTU/h) or less was able to have an energy factor as low as 53%, while under the 2015 standard, the minimum energy factor for a 75-US-gallon gas storage tank water heater is now 74%, which can only be achieved by using condensing technology.

Storage water heaters with a nominal input of 22 kW (75,000 BTU/h) or greater are not currently affected by these requirements, since energy factor is not defined for such units.

An 80 US gal (300 L; 67 imp gal) electric storage tank water heater was able to have a minimum energy factor of 86% under the pre-2015 standard, while under the 2015 standard, the minimum energy factor for an 80-gallon electric storage tank water heater is now 197%, which is only possible with heat pump technology.

[citation needed] (In neither case is the energy expended exploring, developing and extracting coal or natural gas resources included in the quoted efficiency numbers.)

[8] Water heaters potentially can explode and cause significant damage, injury, or death if certain safety devices are not installed.

Furthermore, certain local codes mandate that tank-type heaters in new and retrofit installations must be secured to an adjacent wall by a strap or anchor to prevent tipping over and breaking the water and gas pipes in the event of an earthquake.

[10] For older houses where the water heater is part of the space heating boiler, and plumbing codes allow, some plumbers install an automatic gas shutoff (such as the "Watts 210") in addition to a TPR valve.

The European Guidelines for Control and Prevention of Travel Associated Legionnaires' Disease recommend that hot water should be stored at 60 °C (140 °F) and distributed so that a temperature of at least 50 °C (122 °F) and preferably 55 °C (131 °F) is achieved within one minute at points of use.

[14] If there is a dishwasher without a booster heater, it may require a water temperature within a range of 57–60 °C (135–140 °F) for optimum cleaning,[15] but tempering valves set to no more than 55 °C (131 °F) can be applied to faucets to avoid scalding.

In a paper seeking a green exemption from normal Legionellosis safety standards, Europe's top CEN solar thermal technical committee TC 312 asserts that a 50% fall in performance would occur if solar water heating systems were heated to the base daily.

[citation needed] Legionella pneumophila has been detected at the point of use downstream from horizontally-mounted electric water heaters with volumes of 150 Liters.

In all cases and in particular energy efficient applications, Legionnaires' disease is more often than not the result of engineering design issues that do not take into consideration the impact of stratification or low flow.