Buildings Guide

Domestic Hot Water

Key Message

There are around 98.6 million units of different kinds of water heaters installed in the world by 2013. Brazil and China lead the demand with 28% each followed by North America and Europe with 11% each followed by Japan (4%), Russia (3%), Saudi Arabia (3%), India (2%) and the rest of the countries account for the remaining 10% (Dawson, 2014). This high share of energy consumption for household heating needs including hot water and respective greenhouse gas (GHG) emissions requires priority attention of the policy makers, investors, manufacturers and building contractors.  In addition to greater deployment of SWH and heat pumps replacing the market of less energy efficient water heaters with best available technologies will further decrease environmental emissions and contribute to saving energy. For example, improved efficiency among electric appliances and gas water heaters will reduce CO2 emissions by more than 300 million tons between 2000 and 2020 (Fridley et al., 2007). The following section provides an overview of the potential for energy efficient hot water solutions in different climate regions of the world.


Water is a basic human need. In primitive societies, where the population has traditionally been limited, water used to be extracted from rivers and wells to serve human needs such as bathing, washing clothes and dishes etc. The industrial revolution enabled new techniques for water distribution. This allowed water to become more readily available as pipes became the standard for supplying water to domestic users. With advancing technologies and the demand for better living conditions the demand for heating water rose. Water needs to be heated for human needs like bathing and hand washing especially in winter season and for cooking during the entire year. Different technologies started to develop for heating water for different end-uses including dish washing, laundry, bathing and hand washing which in turn influences energy consumption.


Thermal energy is the main source for domestic and industrial heat around the world (Veerparen & Beerepoot, 2011). The share of residential heat that goes into space and water heating out of total heat ranges from 34 per cent to 39 per cent in OECD (Organization for Economic Cooperation and Development) and BRICS (group of five emerging economies – Brazil, Russia, India, China and South Africa collectively named as BRICS) up to 52 per cent in developing countries. Demand for hot water is significant for bathing, washing clothes and dishes and other end-uses in both developed and developing countries. Hot water consumption depends on uses and application temperature (Mburu, 2009). In Chennai, India for example, following end-use technologies are used for water heating: firewood, animal wastes, liquefied petroleum gas (LPG) stove, geyser, immersion heater and solar water heater (Gopala Krishnan et al., 2003). In Japan hot water use for cooking and bathing accounts for 36 per cent of household energy consumption (Lopes et al., 2004).


A variety of technologies are used for water heating in households around the world. Instantaneous electric water heaters dominated the global water heating market in 2013, commanding highest market share in Brazil followed by electric storage heaters commanding highest shares in China, Europe and North America followed by gas instantaneous water heaters in China, Europe and Japan. Gas storage heaters are popular in North American markets. With around 11 million units of solar thermal water heaters China leads the world market in this segment (Dawson, 2014).


Generally the hot water systems can be classified as conventional (e.g., biomass, gas or electricity based techniques) and non-conventional (e.g., use of solar irradiation or air as heat source). Conventional systems dominate the global water heating market. Electric instantaneous water heaters accounted for highest per cent of the world market for hot water technologies in 2008 (Dawson, 2014). Best available technologies in conventional hot water systems have greater energy efficiency and positive impacts for the environment, economy and health. In warm sunny regions non-conventional solar water heating is cost effective against fossil fuels or electric boilers and their penetration is seen higher in regions with higher solar irradiation like the Middle East and North Africa and southern Europe (on a MW/capita basis). The energy ladder can explain a typical household’s preferred system for hot water. At the bottom of the energy ladder are the households who use conventional biomass fuels like firewood, coal, or animal waste for cooking and water heating. As these households progress on the energy ladder they tend to use more sophisticated energy sources such as LPG, Kerosene gas or electricity. Along with biomass, electricity or gas fired storage and instantaneous water heaters are usually treated as conventional and solar water heaters and heat pumps as non-conventional hot water systems.


Water heating is the third largest domestic energy end-use after space heating/cooling and lighting. This could potentially have a significant contribution to global warming. Using efficient water heaters or turning to alternative energy sources can reduce this contribution. Renewable heating systems, for example, solar water heaters are suitable option especially in warm climates.


Energy efficiency of water heaters can be improved by a variety of measure and design improvement options. Adding insulation to storage tank and pipes could result in reducing standing loss up to 45 per cent. Further, up to 60 per cent of waste heat can be recovered by integrating a spiral tube at the bottom of the heat storage tank. Condensing tankless water heaters use 30 per cent less energy than standard storage models. They use exhaust gas to preheat the cold water before it enters to heat exchanger. SWHs can provide for 100 per cent of household hot water needs in warm and tropical regions. Heat pumps are equally suitable for space heating, cooling and water heating in building.

Efficiency Savings based on BAT

Technology avg. energy savings per unit* Annual Cost Savings (based on 0.12 euro per kWh)
Tanks Insulation 592 kWh 71.04
Tankless heater 521 kWh 62.52
Heat Recovery up to 1,422 kWh 170.64
Heat Pump 2,195 kWh 263.40
Solar Thermal 1,185-2370 kWh 142.20-284.40
* based on medium sized electric storage as reference (with 2,370 kWh/year energy consumption) Source: own calculation and energystar data


Oliver Adria
Ahmad ur Rehman Hafiz


Christopher Moore
Chun Xia


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