ABOUT HOT-WATER CIRCULATION Distant water heaters lead to waste Hot water circulation systems use a pump to circulate hot water from the water heater to the tap, reducing the waiting time for hot water to nearly nothing. All hot water circulation systems save water. But not all systems save energy; some systems actually result in higher energy bills. Choose an on-demand system. There are three types of hot water circulation systems: thermosyphon systems, time and temperature systems, and on-demand systems. On-demand systems make the most sense in a green home because hot water is pumped to the point of use only when it is needed, minimizing standby losses. They’re activated manually or by a wireless remote or motion detector. Such a system is inexpensive to add when plumbing is being roughed in, and can be affordably retrofitted to an existing plumbing system. Installed as a retrofit, on-demand systems use existing cold water lines as the return with the help of a special valve. Time and temperature systems. Hot water is circulated automatically to anticipate demand with the help of a timer and thermostat. An override allows homeowners to activate the pump at non-scheduled times. While time and temperature systems cut waiting time, they increase standby heat losses. Hot water lines are essentially turned into extensions of the hot water storage tank. They save water but increase net energy use. Thermosyphon systems. These work only in a home with a tank-type water heater located below the hot water taps — for example, in a basement. A continuous piping loop is installed between the water heater and the fixtures, with a return line coming back to the heater after the farthest fixture is served. Because the returning water is cooler than the water in the top of the water heater, a thermosyphon…