Energy efficiency of hot water heaters

While some people still use gas- and oil-fired boilers to heat the water in their homes, it is more common to install hot water heaters that incorporate a tank or cylinder that stores hot water. These are generally powered by electricity, propane or natural gas, or by solar energy. Tankless hot water heaters are also becoming much more popular, and these may be operated by gas or electricity.

If you are building a new house or renovating an old one, you will have a myriad of water heating options within these parameters. To make a suitable choice, you should consider:

• generic type (conventional or hybrid gas, conventional or hybrid electric, solar, or tankless)
• energy source (if you have natural gas piped to your home this might be preferable to a conventional electric option; if you are committed to sustainability, solar will be the obvious choice),
• installation requirements (including the size of tank or cylinder and where it needs to be located; instant heaters take up little space, while solar heaters require panels to be installed on your roof),
• cost of the heater itself plus the cost of installation,
• what it's going to cost you to run the water heater (it is often cost effective to spend more on an energy-efficient type and model),
• rebates and incentives that may be offered by national (government) and local authorities in an endeavor to encourage more people to chose energy efficient models and/or change to solar power,
• whether the unit itself is Energy Star rated.

Energy efficient hot water heaters

Countries all over the world have set energy efficiency standards that prescribe the minimum energy performance of manufactured products that require energy to run – including of course hot water heaters.

Energy Star, a joint program of the US Environmental Protection Agency (EPA) and US Department of Energy, has been responsible for manufacturers all over the world using specifications that will allow them to use the Energy Star logo on their products. Wherever you live, when you see the ENERGY STAR, you know that the product meets the very strict energy requirements that have been set by the EPA and the US Department of Energy. According to these partners, Americans saved nearly US$18-billion on their utility bills during 2010 alone – just by using Energy Star-rated appliances.

According to the American Council for an Energy-Efficient Economy (ACEEE), the most common fuel source for hot water heaters in the USA is natural gas which is more energy efficient than propane or electricity. However about 40% of domestic households still currently use electricity to warm their water. Energy Star rated units are available in both categories.

Taking this breakdown further, the Council states that a large percentage of consumers who use natural gas as their fuel of choice, currently choose instantaneous or tankless water heaters. Generally these are much more compact than other types of hot water heaters, and their efficiency ratings are higher than tank units. You can exploit these advantages if you are building new, but if you are renovating, make sure that you are able to incorporate all the necessary ductwork and gas lines – and cost the installation of these carefully. It's not quite as easy to retrofit as it is to install from scratch.

If gas is your fuel of choice, one of the newest types comes in the form of condensing gas water heaters which are said to be even more energy efficient that most other types. These work the same way as conventional tank-type hot water heaters, except that the heat from the combustion gases is trapped and used to heat the water in the tank BEFORE it is vented to the outside environment.

If you prefer to stick with electricity off the grid, an energy efficient option is the heat pump water heater. These units utilize energy from the air to heat the water, and also dehumidify the air, which means you won't need to operate a separate dehumidifier – which you would otherwise have to do if your water heater is located in the basement, or possibly also if you live in a very humid region.