![Active Indirect Water Heater Diagram](https://upload.wikimedia.org/wikipedia/commons/4/46/Active_Indirect_Water_Heater_Diagram.svg)
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to
steam
Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
have many uses.
Domestically, water is traditionally heated in vessels known as ''water heaters'', ''kettles'', ''cauldrons'', ''pots'', or ''coppers''. These metal vessels that heat a batch of water do not produce a continual supply of heated water at a preset temperature. Rarely, hot water occurs naturally, usually from natural
hot spring
A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s. The temperature varies with the consumption rate, becoming cooler as flow increases.
Appliances that provide a continual supply of hot water are called ''water heaters'', ''hot water heaters'', ''
hot water tank
A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use.
Water is a con ...
s'', ''
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
s'', ''
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
s'', ''geysers'' (Southern Africa and the Arab world), or ''calorifiers''. These names depend on region, and whether they heat
potable
Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...
or non-potable water, are in domestic or industrial use, and their energy source. In
domestic
Domestic may refer to:
In the home
* Anything relating to the human home or family
** A domestic animal, one that has undergone domestication
** A domestic appliance, or home appliance
** A domestic partnership
** Domestic science, sometimes c ...
installations, potable water heated for uses other than space heating is also called ''domestic hot water'' (''DHW'').
Fossil fuels (
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
,
liquefied petroleum gas
Liquefied petroleum gas (LPG or LP gas) is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, propylene, butylene, isobutane and n-butane.
LPG is used as a fuel gas in heating appliances, cooking e ...
,
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
), or
solid fuel
Solid fuel refers to various forms of solid material that can be burnt to release energy, providing heat and light through the process of combustion. Solid fuels can be contrasted with liquid fuels and gaseous fuels. Common examples of solid fuels ...
s are commonly used for heating water. These may be consumed directly or may produce
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
that, in turn, heats water. Electricity to heat water may also come from any other electrical source, such as
nuclear power
Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
or
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
.
Alternative energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a Orders of magnitude (time), human timescale. It includes sources such as Solar power, sunlight, wind power, wind, the movement of Hydropo ...
such as
solar energy
Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essenti ...
,
heat pumps
A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing h ...
,
hot water heat recycling, and
geothermal heating
Geothermal heating is the direct use of geothermal energy for some heating applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ o ...
can also heat water, often in combination with backup systems powered by fossil fuels or electricity.
Densely populated urban areas of some countries provide
district heating
District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...
of hot water. This is especially the case in
Scandinavia
Scandinavia; Sámi languages: /. ( ) is a subregion#Europe, subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, ...
,
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
and
Poland
Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...
. District heating systems supply energy for water heating and
space heating
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
from
combined heat and power (CHP) plants such as
incinerator
Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...
s, central heat pumps,
waste heat
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...
from industries, geothermal heating, and
central solar heating
Central solar heating is the provision of central heating and hot water from solar energy by a system in which the water is heated centrally by arrays of solar thermal collectors (central solar heating plants - CSHPs) and distributed through dis ...
. Actual heating of tap water is performed in heat exchangers at the consumers' premises. Generally the consumer has no in-building backup system as redundancy is usually significant on the district heating supply side.
Today in the United States, domestic hot water used in homes is most commonly heated with natural gas, electric resistance, or a heat pump. Electric
heat pump
A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing h ...
water heaters are significantly more efficient than electric resistance water heaters, but also more expensive to purchase. Some energy utilities offer their customers funding to help offset the higher first cost of
energy efficient water heaters.
Types of water heating appliances
![FEMA - 63 - Photograph by Dave Saville taken on 10-04-1999 in North Carolina](https://upload.wikimedia.org/wikipedia/commons/9/96/FEMA_-_63_-_Photograph_by_Dave_Saville_taken_on_10-04-1999_in_North_Carolina.jpg)
Hot water used for space heating may be heated by fossil fuels in a boiler, while
potable water
Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ag ...
may be heated in a separate appliance. This is common practice in the US, especially when warm-air space heating is usually employed.
Storage water heaters (tank-type)
![Boiler and Cylinder](https://upload.wikimedia.org/wikipedia/commons/9/9a/Boiler_and_Cylinder.jpg)
In household and commercial usage, most North American and Southern Asian water heaters are the tank type, also called ''storage water heaters''. These consist of a cylindrical vessel or container that keeps water continuously hot and ready to use. Typical sizes for household use range from 75400
L (20100 US gallons). These may use
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
,
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
,
propane
Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...
,
heating oil
Heating oil is any petroleum product or other oil used for heating; a fuel oil. Most commonly, it refers to low viscosity grades of fuel oil used for furnaces or boilers use for home heating and in other buildings. Home heating oil is often a ...
,
solar, or other energy sources. Natural gas heaters are most popular in the US and most European countries, since the gas is often conveniently piped throughout cities and towns and currently is the cheapest to use. In the United States, typical natural gas water heaters for households without unusual needs are with a burner rated at .
This is a popular arrangement where higher flow rates are required for limited periods. Water is heated in a pressure vessel that can withstand a
hydrostatic pressure
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
close to that of the incoming mains supply. A
pressure reducing valve
A pressure regulator is a valve that controls the pressure of a fluid or gas to a desired value, using negative feedback from the controlled pressure. Regulators are used for gases and liquids, and can be an integral device with a pressure setti ...
is sometimes employed to limit the pressure to a safe level for the vessel. In North America, these vessels are called ''hot water tanks'', and may incorporate an electrical resistance heater, a
heat pump
A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing h ...
, or a gas or oil burner that heats water directly.
Where hot-water space heating boilers are installed,
domestic hot water cylinders are usually heated indirectly by primary water from the boiler, or by an electric
immersion heater
Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. A ...
(often as backup to the boiler). In the UK these vessels are called ''indirect cylinders'' and ''direct cylinders'', respectively. Additionally, if these cylinders form part of a sealed system, providing mains-pressure hot water, they are known as unvented cylinders. In the US, when connected to a boiler, they are called ''indirect-fired water heaters''.
Compared to tankless heaters, storage water heaters have the advantage of using energy (gas or electricity) at a relatively slow rate, storing the heat for later use. The disadvantage is that over time, heat escapes through the tank wall and the water cools down, activating the heating system to heat the water back up, so investing in a tank with better insulation improves this standby efficiency. Additionally, when heavy use exhausts the hot water, there is a significant delay before hot water is available again. Larger tanks tend to provide hot water with less temperature fluctuation at moderate flow rates.
Volume storage water heaters in the United States and New Zealand are typically vertical cylindrical tanks, usually standing on the floor or on a platform raised a short distance above the floor. Volume storage water heaters in Spain are typically horizontal. In India, they are mainly vertical. In apartments they can be mounted in the ceiling space over laundry-utility rooms. In Australia, gas and electric outdoor tank heaters have mainly been used (with high temperatures to increase effective capacity), but solar roof tanks are becoming fashionable.
Tiny ''point-of-use'' (POU) electric storage water heaters with capacities ranging from 832 L (26 gallons) are made for installation in kitchen and bath cabinets or on the wall above a sink. They typically use low power
heating element
A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independe ...
s, about 1 kW to 1.5 kW, and can provide hot water long enough for hand washing, or, if plumbed into an existing hot water line, until hot water arrives from a remote high capacity water heater. They may be used when retrofitting a building with hot water plumbing is too costly or impractical. Since they maintain water temperature thermostatically, they can only supply a continuous flow of hot water at extremely low flow rates, unlike high-capacity tankless heaters.
In tropical countries like Singapore and India, a storage water heater may vary from 10 L to 35 L. Smaller water heaters are sufficient, as ambient weather temperatures and incoming water temperature are moderate. The Coldest regions in India like Kashmir, people are mostly dependent on the storage type electric water heaters. Mostly 50L or 75L Storage type electric water heaters are connected to overhead water source.
Point-of-use (POU) vs centralized hot water
A locational design decision may be made between point-of-use and centralized water heaters. Centralized water heaters are more traditional, and are still a good choice for small buildings. For larger buildings with intermittent or occasional hot water use, multiple POU water heaters may be a better choice, since they can reduce long waits for hot water to arrive from a remote heater. The decision where to locate the water heater(s) is only partially independent of the decision of a tanked vs.
tankless water heater
Tankless water heaters — also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters — are water heaters that instantly heat water as it flows through the device, and do not retain any water internally e ...
, or the choice of energy source for the heat.
Instantaneous water heaters (tankless-type)
![Water heater bathroom](https://upload.wikimedia.org/wikipedia/commons/b/b8/Water_heater_bathroom.JPG)
Tankless water heaters—also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters—are gaining in popularity. These high-power water heaters instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil.
Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication.
Tankless heaters may be installed throughout a household at more than one point-of-use (POU), far from a central water heater, or larger centralized models may still be used to provide all the hot water requirements for an entire house. The main advantages of tankless water heaters are a plentiful continuous flow of hot water (as compared to a limited flow of continuously heated hot water from conventional tank water heaters), and potential energy savings under some conditions. 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. In a comparison to a less efficient natural gas fired hot water tank, on-demand natural gas will cost 30% more over its useful life.
Stand-alone appliances for quickly heating water for domestic usage are known in North America as ''tankless'' or ''on demand'' water heaters. In some places, they are called ''multipoint heaters'', ''geysers'' or ''ascots''. In Australia and New Zealand they are called ''instantaneous hot water units''. In Argentina they are called ''calefones''. In that country ''calefones'' use gas instead of electricity, although gas powered tankless water heaters can also be found in other countries. A similar wood-fired appliance was known as the
chip heater
The chip heater is a single point, tankless, domestic hot water system popular in Australia and New Zealand from the 1880s until the 1960s. Examples of this form of domestic water heater are still in use.
The chip heater consisted of a cylindr ...
.
A common arrangement where hot-water space heating is employed is for a boiler also to heat
potable water
Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ag ...
, providing a continuous supply of hot water without extra equipment. Appliances that can supply both space-heating and domestic hot water are called ''combination'' (or ''combi'') boilers. Though on-demand heaters provide a continuous supply of domestic hot water, the rate at which they can produce it is limited by the thermodynamics of heating water from the available fuel supplies.
Electric shower heads
![Showers in Guatemala](https://upload.wikimedia.org/wikipedia/commons/4/4e/Showers_in_Guatemala.JPG)
An electric shower head has an
electric heating
Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. An ...
element which heats water as it passes through. These self-heating shower heads are specialized point-of-use (POU) tankless water heaters, and are widely used in some countries.
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. Earlier models were made of chromed copper or brass, which were expensive, but since 1970, units made of injected plastics are popular due to low prices similar to that of a hair dryer. Electric showers have a simple electric system, working like a coffee maker, but with a larger water flow. A flow switch turns on the device when water flows through it. Once the water is stopped, the device turns off automatically. An ordinary electric shower often but not always has three heat settings: high (5.5 kW), low (2.5 kW), or cold (0 W) to use when a central heater system is available or in hot seasons. Higher power (up to 7.5 KW) and lower power (up to 3.2 KW) versions are also made, as well as versions with 4 heat settings or a variable heat setting.
Energy usage
The power consumption of electric showers in the max. heating setting is about 5.5 kW for 120 V and 7.5 kW for 220 V. The lower costs with electric showers compared to the higher costs with tank boilers is due to the time of use: an electric shower uses energy only while the water flows, while a tank boiler works many times a day to keep a quantity of standing water hot for use throughout the day and night. Moreover, the transfer of electric energy to the water in an electric shower head is very efficient, approaching 100%. Electric showers may save energy compared to electric tank heaters, which lose some standby heat.
Safety
There is a wide range of electric shower heads, with various designs and types of heating controls. The heating element of an electric shower is immersed in the water stream, using an often replaceable
nichrome
Nichrome (also known as NiCr, nickel-chromium or chromium-nickel) is a family of alloys of nickel, chromium, and often iron (and possibly other elements) commonly used as resistance wire, heating elements in devices like toasters, electrical kettl ...
resistive heating element which is often not sheathed and electrically isolated, in which case isolation is provided by earthing electrodes that directly touch the water before it exits the head. Electric shower heads with sheathed and electrically isolated heating elements are often marketed as such (Chuveiros blindados in Portuguese) and are more expensive. Due to electrical safety standards as well as cost, modern electric showers are made of plastic instead of using metallic casings like in the past. As an electrical appliance that uses more electric current than a clothes washer or a hair dryer, an electric shower installation requires careful planning, and generally is intended to be wired directly from the electrical distribution box with a dedicated
circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
and ground system. A poorly installed system with old aluminum wires, bad connections or an unconnected ground wire (which is often the case) may be dangerous, as the wires can overheat or electric current may leak via the water stream through the body of the user to earth.
Solar water heaters
![Flat-plate solar thermal collector, viewed from roof-level](https://upload.wikimedia.org/wikipedia/commons/3/33/Flat-plate_solar_thermal_collector%2C_viewed_from_roof-level.png)
Increasingly,
solar powered
Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essenti ...
water heaters are being used. Their solar collectors are installed outside dwellings, typically on the roof or walls or nearby, and the potable
hot water storage tank
A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use.
Water is a con ...
is typically a pre-existing or new conventional water heater, or a water heater specifically designed for solar thermal. In
Cyprus
Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is geo ...
and
Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
90 percent of homes have solar water heating systems.
The most basic solar thermal models are the direct-gain type, in which the potable water is directly sent into the collector. Many such systems are said to use ''integrated collector storage'' (ICS), as direct-gain systems typically have storage integrated within the collector. Heating water directly is inherently more efficient than heating it indirectly via heat exchangers, but such systems offer very limited freeze protection (if any), can easily heat water to temperatures unsafe for domestic use, and ICS systems suffer from severe heat loss on cold nights and cold, cloudy days.
By contrast, ''indirect'' or ''closed-loop'' systems do not allow potable water through the panels, but rather pump a heat transfer fluid (either water or a water/antifreeze mix) through the panels. After collecting heat in the panels, the heat transfer fluid flows through a
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
, transferring its heat to the potable hot water. When the panels are cooler than the storage tank or when the storage tank has already reached its maximum temperature, the controller in closed-loop systems stops the circulation pumps. In a ''drainback'' system, the water drains into a storage tank contained in conditioned or semi-conditioned space, protected from freezing temperatures. With antifreeze systems, however, the pump ''must'' be run if the panel temperature gets too hot (to prevent degradation of the antifreeze) or too cold (to prevent the water/antifreeze mixture from freezing.)
''Flat panel collectors'' are typically used in closed-loop systems. Flat panels, which often resemble
skylights
A skylight (sometimes called a rooflight) is a light-permitting structure or window, usually made of transparent or translucent glass, that forms all or part of the roof space of a building for daylighting and ventilation purposes.
History
Open ...
, are the most durable type of collector, and they also have the best performance for systems designed for temperatures within of
ambient temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
. Flat panels are regularly used in both pure water and antifreeze systems.
Another type of solar collector is the ''evacuated tube collector'', which are intended for cold climates that do not experience severe hail and/or applications where high temperatures are needed (i.e., over ). Placed in a rack, evacuated tube collectors form a row of glass tubes, each containing absorption fins attached to a central heat-conducting rod (copper or condensation-driven). The ''evacuated'' description refers to the vacuum created in the glass tubes during the manufacturing process, which results in very low heat loss and lets evacuated tube systems achieve extreme temperatures, far in excess of water's boiling point.
Geothermal heating
In countries like
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
and
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, and other volcanic regions, water heating may be done using
geothermal heating
Geothermal heating is the direct use of geothermal energy for some heating applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ o ...
, rather than combustion.
Gravity-fed system
Where a space-heating water boiler is employed, the traditional arrangement in the UK is to use boiler-heated (''primary'') water to heat potable (''secondary'') water contained in a cylindrical vessel (usually made of copper)—which is supplied from a cold water storage vessel or container, usually in the roof space of the building. This produces a fairly steady supply of DHW (domestic hot water) at low
static pressure head but usually with a good
flow. In most other parts of the world, water heating appliances do not use a cold water storage vessel or container, but heat water at pressures close to that of the incoming
mains water
A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following:
# A drainage basin (see water purification – sourc ...
supply.
Other improvements
Other improvements to water heaters include check valve devices at their inlet and outlet, cycle timers, electronic
ignition
Ignition may refer to:
Science and technology
* Firelighting, the human act of creating a fire for warmth, cooking and other uses
* Combustion, an exothermic chemical reaction between a fuel and an oxidant
* Fusion ignition, the point at which a ...
in the case of fuel-using models, sealed air intake systems in the case of fuel-using models, and pipe insulation. The sealed air-intake system types are sometimes called "band-
joist
A joist is a horizontal structural member used in framing to span an open space, often between beams that subsequently transfer loads to vertical members. When incorporated into a floor framing system, joists serve to provide stiffness to the s ...
" intake units. "High-efficiency" condensing units can convert up to 98% of the energy in the fuel to heating the water. The exhaust gases of combustion are cooled and are mechanically
ventilated either through the roof or through an exterior wall. At high
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
efficiencies a drain must be supplied to handle the water condensed out of the combustion products, which are primarily carbon dioxide and water vapor.
In traditional plumbing in the UK, the space-heating boiler is set up to heat a separate ''hot water cylinder'' or ''water heater'' for potable hot water. Such water heaters are often fitted with an auxiliary electrical ''immersion heater'' for use if the boiler is out of action for a time. Heat from the space-heating boiler is transferred to the water heater vessel/container by means of a heat exchanger, and the boiler operates at a higher temperature than the potable hot water supply. Most potable water heaters in North America are completely separate from the space heating units, due to the popularity of
HVAC
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
/
forced air
A forced-air central heating system is one which uses air as its heat transfer medium. These systems rely on ductwork, vents, and plenums as means of air distribution, separate from the actual heating and air conditioning systems. The return p ...
systems in North America.
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
The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
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. The second feature prevents tank overheating due to unusual combustion conditions. These safety requirements were made in response to homeowners storing, or spilling,
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
or other flammable liquids near their water heaters and causing fires. Since most of the new designs incorporate some type of
flame arrestor
A flame arrester (also spelled arrestor), deflagration arrester,
or flame trap
are safety devices fitted to openings of enclosures or to pipe work, and are intended to allow flow but prevent flame transmission fuel combustion by extinguishing the ...
screen, they require monitoring to make sure they do not become clogged with lint or dust, reducing the availability of air for combustion. If the flame arrestor becomes clogged, the thermal cutoff may act to shut down the heater.
A ''wetback stove'' (
NZ), ''wetback heater'' (NZ), or ''back boiler'' (UK), is a simple household secondary water heater using incidental heat. It typically consists of a hot water pipe running behind a
fireplace
A fireplace or hearth is a structure made of brick, stone or metal designed to contain a fire. Fireplaces are used for the relaxing ambiance they create and for heating a room. Modern fireplaces vary in heat efficiency, depending on the design.
...
or
stove
A stove or range is a device that burns fuel or uses electricity to generate heat inside or on top of the apparatus, to be used for general warming or cooking. It has evolved highly over time, with cast-iron and induction versions being develope ...
(rather than
hot water storage
A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use.
Water is a con ...
), and has no facility to limit the heating. Modern wetbacks may run the pipe in a more sophisticated design to assist
heat-exchange
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
. These designs are being forced out by government efficiency regulations that do not count the energy used to heat water as 'efficiently' used.
History
![Kerosene water heater, 1917](https://upload.wikimedia.org/wikipedia/commons/f/f4/Kerosene_water_heater%2C_1917.jpg)
Another type of water heater developed in Europe predated the storage model. In London, England, in 1868, a painter named Benjamin Waddy Maughan invented the first instantaneous domestic water heater that did not use
solid fuel
Solid fuel refers to various forms of solid material that can be burnt to release energy, providing heat and light through the process of combustion. Solid fuels can be contrasted with liquid fuels and gaseous fuels. Common examples of solid fuels ...
. Named the ''
geyser
A geyser (, ) is a spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditions that exist only in ...
'' after an Icelandic gushing hot spring, Maughan's invention made cold water at the top flow through pipes that were heated by hot gases from a burner at the bottom. Hot water then flowed into a sink or tub. The invention was somewhat dangerous because there was no flue to remove heated gases from the bathroom. A water heater is still sometimes called a ''geyser'' in the UK.
Maughn's invention influenced the work of a Norwegian mechanical engineer named
Edwin Ruud
Edwin Ruud (9 June 1854 – 9 December 1932) was a Norwegian-American mechanical engineer and inventor who immigrated to the United States where he designed, sold, and popularized the tankless water heater. He was the founder and President of Ruu ...
. The first automatic, storage tank-type gas water heater was invented around 1889 by Ruud after he immigrated to
Pittsburgh, Pennsylvania
Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, United States, and the county seat of Allegheny County, Pennsylvania, Allegheny County. It is the most populous city in both Allegheny County and Wester ...
(US). The Ruud Manufacturing Company, still in existence today, made many advancements in tank-type and tankless water heater design and operation.
Thermodynamics and economics
![ModCon boiler system](https://upload.wikimedia.org/wikipedia/commons/8/86/ModCon_boiler_system.jpg)
Water typically enters residences in the US at about , depending on latitude and season. Hot water temperatures of are usual for dish-washing, laundry and showering, which requires that the heater raise the water temperature about if the hot water is mixed with cold water at the point of use. The
Uniform Plumbing Code
Designated as an American National Standard, the Uniform Plumbing Code (UPC) is a model code developed by the International Association of Plumbing and Mechanical Officials (IAPMO) to govern the installation and inspection of plumbing systems as ...
reference shower flow rate is per minute. Sink and dishwasher usages range from per minute.
Natural gas is often measured by volume or heat content. Common units of measurement by volume are
cubic metre
The cubic metre (in Commonwealth English and international spelling as used by the International Bureau of Weights and Measures) or cubic meter (in American English) is the unit of volume in the International System of Units (SI). Its symbol is m ...
or
cubic feet
Cubic may refer to:
Science and mathematics
* Cube (algebra), "cubic" measurement
* Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex
** Cubic crystal system, a crystal system ...
at
standard conditions
Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union o ...
or by heat content in
kilowatt hour
A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
s,
British thermal unit
The British thermal unit (BTU or Btu) is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is also part of the United States customary units. The modern SI ...
s (BTU) or
therm
The therm (symbol, thm) is a non- SI unit of heat energy equal to 100,000 British thermal units (BTU), and approximately megajoules, kilowatt-hours, kilocalories and thermies. One therm is the energy content of approximately of natural gas at s ...
, which is equal to 100,000 BTU. A BTU is the energy required to raise one pound of water by one degree Fahrenheit. A US gallon of water weighs . To raise of water from to at 90% efficiency requires . A heater, as might exist in a tankless heater, would take about 15 minutes to do this. At $1 per
therm
The therm (symbol, thm) is a non- SI unit of heat energy equal to 100,000 British thermal units (BTU), and approximately megajoules, kilowatt-hours, kilocalories and thermies. One therm is the energy content of approximately of natural gas at s ...
, the cost of the gas would be about 40 cents. In comparison, a typical tank electric water heater has a heating element, which at 100% efficient results in a heating time of about 2.34 hours. At $0.16/kWh the electricity would cost $1.68.
Energy efficiencies of water heaters in residential use can vary greatly, particularly depending on manufacturer and model. However, electric heaters tend to be slightly more efficient (not counting power station losses) with recovery efficiency (how efficiently energy transfers to the water) reaching about 98%. Gas-fired heaters have maximum recovery efficiencies of only about 8294% (the remaining heat is lost with the flue gasses). Overall
energy factor An energy factor is a metric used in the United States to compare the energy conversion efficiency of residential appliances and equipment. The energy factor is currently used for rating the efficiency of water heaters, dishwashers, clothes washer ...
s can be as low as 80% for electric and 50% for gas systems. Natural gas and propane tank water heaters with energy factors of 62% or greater, as well as electric tank water heaters with energy factors of 93% or greater, are considered high-efficiency units.
Energy Star
Energy Star (trademarked ''ENERGY STAR'') is a program run by the U.S. Environmental Protection Agency (EPA) and U.S. Department of Energy (DOE) that promotes energy efficiency. The program provides information on the energy consumption of pro ...
-qualified natural gas and propane tank water heaters (as of September 2010) have energy factors of 67% or higher, which is usually achieved using an intermittent pilot together with an automatic flue damper, baffle blowers, or power venting. Direct electric resistance tank water heaters are not included in the Energy Star program, however, the Energy Star program does include electric
heat pump
A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing h ...
units with energy factors of 200% or higher. Tankless gas water heaters (as of 2015) must have an energy factor of 90% or higher for Energy Star qualification. Since electricity production in thermal plants has efficiency levels ranging from only 15% to slightly over 55% (
combined cycle
A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turb ...
gas turbine), with around 40% typical for thermal power stations, direct resistance electric water heating may be the least energy efficient option. However, use of a heat pump can make electric water heaters much more energy efficient and lead to a decrease in carbon dioxide emissions, even more so if a
low carbon
A low-carbon economy (LCE) or decarbonised economy is an economy based on energy sources that produce low levels of greenhouse gas (GHG) emissions. GHG emissions due to human activity are the dominant cause of observed climate change since the mi ...
source of electricity is used. Using
district heating
District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...
utilizing waste heat from
electricity generation
Electricity generation is the process of generating electric power from sources of primary energy. For electric utility, utilities in the electric power industry, it is the stage prior to its Electricity delivery, delivery (Electric power transmi ...
and other industries to heat residences and hot water gives an increased overall efficiency, removing the need for burning fossil fuel or using high energy value electricity to produce heat in the individual home.
Unfortunately, it takes a great deal of energy to heat water, as one may experience when waiting to boil a gallon of water on a stove. For this reason, tankless on-demand water heaters require a powerful energy source. A standard 120-V, 15-ampere rated wall electric outlet, by comparison, only sources enough power to warm a disappointingly small amount of water: about per minute at 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.
[M.J. Booysen, J.A.A. Engelbrecht, M.J. Ritchie, M. Apperley, A.H. Cloete, "How much energy can optimal control of domestic water heating save?", ''Energy for Sustainable development'', ''Vol 51'', Aug 2019. published: https://doi.org/10.1016/j.esd.2019.05.004 (open: https://doi.org/10.31224/osf.io/xnq4t)]
US minimum requirements
On April 16, 2015, as part of the
National Appliance Energy Conservation Act
The National Appliance Energy Conservation Act of 1987 (NAECA; ) is a United States Act of Congress that regulates energy consumption of specific household appliances. Though minimum Energy Efficiency Standards were first established by the Unite ...
(NAECA), new minimum standards for efficiency of residential water heaters set by the
United States Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...
went into effect. All new gas storage tank water heaters with capacities smaller than sold in the United States in 2015 or later shall have an energy factor of at least 60% (for 50-US-gallon units, higher for smaller units), increased from the pre-2015 minimum standard of 58% energy factor for 50-US-gallon gas units. Electric storage tank water heaters with capacities less than 55 US gallons sold in the United States shall have an energy factor of at least 95%, increased from the pre-2015 minimum standard of 90% for 50-US-gallon electric units.
Under the 2015 standard, for the first time, storage water heaters with capacities of 55 US gallons or larger now face stricter efficiency requirements than those of 50 US gallons or less. Under the pre-2015 standard, a gas storage water heater with a nominal input of 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 or greater are not currently affected by these requirements, since energy factor is not defined for such units. An 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
A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing h ...
technology. This rating measures efficiency at the point of use. Depending on how electricity is generated, overall efficiency may be much lower. For example, in a traditional coal plant, only about 30–35% of the energy in the coal ends up as electricity on the other end of the generator.
Losses on the electrical grid (including line losses and voltage transformation losses) reduce electrical efficiency further. According to data from the Energy Information Administration, transmission and distribution losses in 2005 consumed 6.1% of net generation.
In contrast, 90% of natural gas’s energy value is
delivered to the consumer. (In neither case is the energy expended exploring, developing and extracting coal or natural gas resources included in the quoted efficiency numbers.) Gas tankless water heaters shall have an energy factor of 82% or greater under the 2015 standards, which corresponds to the pre-2015 Energy Star standard.
In 2022 the Department of Energy proposed rules that would take effect in 2026 and would effectively eliminate inefficient non-condensing gas water heaters in commercial buildings. Non-condensing models waste heat, while condensing models capture and used otherwise lost energy.
The change will reduce emissions by 38 million tons of carbon dioxide over 30 years and reduce buildings' energy costs.
Water heater safety
Explosion hazard
![WH safety valve](https://upload.wikimedia.org/wikipedia/commons/9/94/WH_safety_valve.JPG)
Water heaters potentially can explode and cause significant damage, injury, or death if certain safety devices are not installed. A safety device called a
temperature and pressure relief (T&P or TPR) valve, is normally fitted on the top of the water heater to dump water if the temperature or pressure becomes too high. Most plumbing codes require that a discharge pipe be connected to the valve to direct the flow of discharged hot water to a drain, typically a nearby
floor drain
A floor drain is a plumbing fixture that is installed in the floor of a structure, mainly designed to remove any standing water near it. They are usually round, but can also be square or rectangular. They usually range from ; most are {{convert, ...
, or outside the living space. Some building codes allow the discharge pipe to terminate in the garage.
If a gas or propane fired water heater is installed in a
garage
A garage is a covered structure built for the purpose of parking, storing, protecting, maintaining, and/or repairing vehicles. Specific applications include:
*Garage (residential), a building or part of a building for storing one or more vehicle ...
or basement, many plumbing codes require that it be elevated at least above the floor to reduce the potential for fire or explosion due to spillage or leakage of combustible liquids in the garage. 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
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
.
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. When the device senses that the temperature reaches , it shuts off the gas supply and prevents further heating. In addition, an
expansion tank
An expansion tank or expansion vessel is a small tank used to protect closed (not open to atmospheric pressure) water heating systems and domestic hot water systems from excessive pressure. The tank is partially filled with air, whose compressibili ...
or exterior pressure relief valve must be installed to prevent pressure buildup in the plumbing from rupturing pipes, valves, or the water heater.
Thermal burns (scalding)
Scalding
Scalding is a form of thermal burn resulting from heated fluids such as boiling water or steam. Most scalds are considered first- or second-degree burns, but third-degree burns can result, especially with prolonged contact. The term is from the L ...
is a serious concern with any water heater.
Human skin
The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue guarding muscles, bones, ligaments and internal organs. Human skin is similar to most ...
burn
A burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur mainl ...
s quickly at high temperature, in less than 5 seconds at , but much slower at — it takes a full minute for a
second degree burn
A burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur mai ...
. Older people and children often receive serious scalds due to disabilities or slow
reaction time
Mental chronometry is the scientific study of processing speed or reaction time on cognitive tasks to infer the content, duration, and temporal sequencing of mental operations. Reaction time (RT; sometimes referred to as "response time") is meas ...
s.
[''Domestic Water Heating Design Manual (2nd Edition)'', American Society of Plumbing Engineers (ASPE), 2003, pages 13–14] In the United States and elsewhere it is common practice to put a ''tempering valve'' (
Thermostatic mixing valve
A thermostatic mixing valve (TMV) is a valve that blends hot water with cold water to ensure constant, safe shower and bath outlet temperatures, preventing scalding.
The storage of water at high temperature removes one possible breeding ground ...
) on the outlet of the water heater. The result of ''automatically'' mixing hot and cold water via a tempering valve is referred to as "tempered water".
A tempering valve mixes enough cold water with the hot water from the heater to keep the outgoing water temperature fixed at a more moderate temperature, often set to . Without a tempering valve, reduction of the water heater's setpoint temperature is the most direct way to reduce scalding. However, for sanitation, hot water is needed at a temperature that can cause scalding. This may be accomplished by using a supplemental heater in an appliance that requires hotter water.
Most residential
dishwashing machine
A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, ...
s, for example, include an internal electric heating element for increasing the water temperature above that provided by a domestic water heater.
Bacterial contamination
![LegionellaPneumophila Kolonie](https://upload.wikimedia.org/wikipedia/commons/a/a7/LegionellaPneumophila_Kolonie.jpg)
Two conflicting safety issues affect water heater temperature—the risk of scalding from excessively hot water greater than , and the risk of incubating bacteria colonies, particularly ''
Legionella
''Legionella'' is a genus of pathogenic gram-negative bacteria that includes the species '' L. pneumophila'', causing legionellosis (all illnesses caused by ''Legionella'') including a pneumonia-type illness called Legionnaires' disease and a mi ...
'', in water that is not hot enough to kill them. Both risks are potentially life-threatening and are balanced by setting the water heater's thermostat to . The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at and distributed so that a temperature of at least and preferably is achieved within one minute at points of use.
If there is a dishwasher without a booster heater, it may require a water temperature within a range of for optimum cleaning,
but tempering valves set to no more than can be applied to faucets to avoid scalding. Tank temperatures above may produce
limescale
Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of old ...
deposits, which could later harbor bacteria, in the water tank. Higher temperatures may also increase
etching of glassware in the dishwasher.
Tank thermostats are not a reliable guide to the internal temperature of the tank. Gas-fired water tanks may have no temperature calibration shown. An electric thermostat shows the temperature at the elevation of the thermostat, but water lower in the tank can be considerably cooler. An outlet thermometer is a better indication of water temperature.
[Donald R. Wulfinghoff ''Energy Efficiency Manual''Energy Institute Press, 1999 pages 458–460]
In the
renewable energy industry
The renewable-energy industry is the part of the energy industry focusing on new and appropriate renewable energy technologies. Investors worldwide have paid greater attention to this emerging industry in recent years. In many cases, this has tra ...
(solar and heat pumps, in particular) the conflict between daily thermal Legionella control and high temperatures, which may drop system performance, is subject to heated debate. 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. However some
solar simulator analysis work using Polysun 5 suggests that an 11% energy penalty is a more likely figure. Whatever the context, both energy efficiency and scalding safety requirements push in the direction of considerably lower water temperatures than the legionella
pasteurization
Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life.
The ...
temperature of around .
Legionella pneumophila has been detected at the point of use downstream from horizontally-mounted electric water heaters with volumes of 150 Liters.
[W. Stone, T.M. Louw, G. Gakingo, M.J. Nieuwoudt, M.J. Booysen, "A potential source of undiagnosed Legionellosis: Legionella growth in domestic water heating systems in South Africa", ''Energy for Sustainable development'', ''Vol 49'', Feb 2019. published: https://doi.org/10.1016/j.esd.2018.12.001 (open: https://doi.org/10.31224/osf.io/23fzc)]
However, legionella can be safely and easily controlled with good design and engineering protocols. For instance raising the temperature of water heaters once a day or even once every few days to at the coldest part of the water heater for 30 minutes effectively controls legionella. 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.
It is also possible to control Legionella risks by chemical treatment of the water. This technique allows lower water temperatures to be maintained in the pipework without the associated Legionella risk. The benefit of lower pipe temperatures is that the heat loss rate is reduced and thus the energy consumption is reduced.
See also
*
Aquastat
An aquastat is a device used in hydronic heating systems for controlling water temperature. To prevent the boiler from firing too frequently, aquastats have a high limit temperature and a low limit. If the thermostat
A thermostat is a ...
*
Architectural engineering
Architectural engineers apply and theoretical knowledge to the engineering design of buildings and building systems. The goal is to engineer high performance buildings that are sustainable, economically viable and ensure the safety health.
Archi ...
*
Condensing boiler
Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency (greater than 90% on the higher heating value) by cond ...
*
Electric water boiler
An electric water boiler, also called a thermo pot, is a consumer electronics small appliance used for boiling water and maintaining it at a constant temperature in an enclosed reservoir. It is typically used to provide an immediate source of h ...
*
Energy conservation
Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less energy for continuous service) or changing one's behavior to use less service (f ...
*
Heat trap
*
Joule heating
Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor (material), conductor produces heat.
Joule's first law (also just Joule's law), also known in c ...
*
List of home appliances
This is a list of home appliances. A home appliance is a device which accomplishes household functions, such as cooking or cleaning. Home appliances can be classified into:
* Major appliances
* Small appliances
* Consumer electronics
See also
...
*
Outdoor wood-fired boiler
The outdoor wood boiler is a variant of the classic wood stove adapted for set-up outdoors while still transferring the heat to interior buildings.
Technology
The outdoor wood boiler is a variant on the indoor wood, oil or gas boiler. An outdoor ...
*
Solar water heating
Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential a ...
*
Thermal immersion circulator
A thermal immersion circulator is an electrically powered device that circulates and heats a warm fluid kept at an accurate and stable temperature. It is used in process, environmental, microbiological, hazardous waste, and other laboratories. Sin ...
*
Water heat recycling
Water heat recycling (also known as drain water heat recovery, waste water heat recovery, greywater heat recovery, or sometimes shower water heat recovery) is the use of a heat exchanger to recover energy and reuse heat from drain water from vario ...
References
External links
How It Works - Water Heaterfrom ''
Popular Mechanics
''Popular Mechanics'' (sometimes PM or PopMech) is a magazine of popular science and technology, featuring automotive, home, outdoor, electronics, science, do-it-yourself, and technology topics. Military topics, aviation and transportation o ...
''
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