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Office of Energy Efficiency Links


Personal: Residential


Hydronic Systems - Electric

Electric hot water (hydronic) systems deliver heat to a house by means of hot water. They have three main components:

  • a boiler to heat the water
  • heating equipment – generally baseboards or radiators – in most rooms, often installed against an outside wall
  • a pump to circulate water from the boiler through the pipes to the radiator and back again

Central boiler for an electric hydronic system

Central boiler for an electric hydronic system

The boiler in an electric hot water heating system is compact. Its heating elements are immersed directly in the water (as in an electric kettle). Where space is limited, the boiler can be installed on a basement wall, in a closet or under a kitchen cabinet. It can even be hung from basement ceiling joists.

Maximizing Efficiency in Hydronic Systems

There are several ways to improve the performance of hydronic heating systems.

Improving Heat Distribution

Old-fashioned gravity heating systems that circulate water by natural convection are less efficient than systems with a circulating pump. Slow heat circulation may cause house temperatures to fluctuate noticeably between firing cycles. As with all hydronic systems, it can also take a long time to restore the house temperature after a nighttime thermostat setback. In addition, a gravity system cannot circulate hot water to radiators or baseboards in basement living areas, where they would be below the level of the boiler. All of these problems can be overcome by adding a circulating pump and replacing the open expansion tank with a sealed and pressurized expansion tank near the boiler. If you have a gravity system, ask your plumbing and heating contractor about upgrading it.

Balancing the Heat

Manual valve Balancing the heat delivered to different areas of the house is as important with hydronic heating as it is with a forced-air system. Radiators are often fitted with a simple manual valve that can be used to control the amount of water flowing through them. Such valves can be used to vary the heat delivered to different rooms of the house in the same way that balancing dampers are used in a forced-air system.

Automatic valve One device that can vary the heat output automatically is a thermostatic valve, which can be set to control the temperature in any room. This valve, however, will not work on radiators or baseboards installed on a "series loop" system. In such a system, the water must pass through all the radiators on its way back to the boiler. If there is more than one loop in the system, the heat output can be balanced somewhat by adjusting the valves that control the water flow through each loop. The heat output of baseboard units can also be controlled to some extent by regulating the built-in damper, which operates much like the damper in a warm-air register.

Zone control It is possible to reduce energy use in a hydronic system through zone control. This system regulates the temperature of individual rooms with thermostat-controlled valves on each radiator. A plumbing and heating contractor can provide more information about zone control and can install all required equipment when the heating system is installed.

Outdoor reset Conventional hydronic systems usually have the boiler temperature set at 82oC (180oF). In some hydronic systems, it is possible to reduce energy consumption by means of a regulator valve that varies the temperature of the water circulating in the system in relation to the temperature outside. As it becomes warmer outside, the temperature of the water is reduced.

However, some boilers can be subject to thermal shock or corrosion if the return water temperature is too cold. Before applying one of these devices to your system, ask your plumbing and heating contractor whether your boiler can handle it, and if the distribution system will perform effectively at the lower temperature.


The easiest way to save heating dollars is to lower the temperature setting on your house thermostat when possible.

Automatic setback thermostats will adjust your home’s temperature automatically. These thermostats have a mechanical or electronic timer that allows you to preset household temperatures for specific periods of the day and night. As a general rule, you will save 2 percent on your heating bill for every 1°C you turn down the thermostat overnight.

You could program the thermostat to reduce the temperature a short while before you go to bed and to raise it again before you get up in the morning. You could also program it to reduce the temperature for any period during the day when the house is unoccupied and to restore the temperature shortly before you return. A good guide is to have the temperature set at 17°C (63°F) when you are sleeping or not at home and at 20°C (68°F) when you are awake and home.

ENERGY STAR qualified programmable thermostat can help reduce the temperature swing from an average range of 1.5–2°C to 0. 5–1°C, ensuring that the heating system turns on and off as close to the required temperatures as possible. Energy savings from these mechanisms will be maximized and comfort is usually enhanced at the same time.