What Are Hot Water Recirculating Systems?

Hot Water Recirculation Systems are often used to circulate domestic hot water so that a faucet will provide hot water instantly upon demand. In regions where water conservation issues are rising in importance with rapidly expanding and urbanizing populations local water authorities offer rebates to homeowners and builders that install a hot water recirculation system to save water.

In typical one-way plumbing without a recirculation system, water is simply piped from the water heater through the pipes to the tap. Once the tap is shut off, the water remaining in the pipes cools producing the familiar wait for hot water the next time the tap is opened. By adding a recirculation system and constantly circulating a small amount of hot water through the pipes from the heater to the furthest fixture and back to the heater, the water in the pipes is always hot, and no water is wasted during the wait.

While the majority of these systems require a pump and have no adjustable temperature capabilities, a significant reduction in energy can be achieved by utilizing a temperature adjustable thermostatically controlled recirculation valve mounted at the last fixture on the loop. Thermostatically controlled valves allow owners to choose the desired temperature of hot water to be maintained within the hot water pipes. Thermostatically controlled recirculation valves (not requiring a water pump) cycle on and off to maintain a user’s chosen temperature and consume less energy than a continuously operating pump. By installing a thermostatically controlled valve just at the farthest fixture on the loop, convection circulated hot water reaches the entire loop which also can prevent pipe freezing.

Installing a circulation pump on a hot water circulation loop can be difficult due to limited available space, cosmetics, noise restrictions or lack of available power. Recent advancements in hot water circulation technology allow for benefiting from temperature controlled hot water circulation without having to install the pump. These advanced hot water circulation systems utilize a water contacting temperature probe strategically installed at the last fixture on the loop. Thermal insulation applied to the pipes helps mitigate this second loss and minimize the amount of water that must be pumped to keep hot water constantly available.

The traditional hot water recirculation system uses a dedicated return line from the point of use located farthest from the hot water tank back to the hot water tank. In homes where this return line was not installed the cold water line is used as a return line.  Reduced energy waste and discomfort is possible by preventing occurrences of hot water line siphoning in open-loop hot water circulation systems which utilize the cold water line to return water back to the water heater. Hot Water Line Siphoning occurs when water from within the hot water line siphons or is forced into the cold water line due to differences in water pressure between the hot and cold water lines. Utilizing a temperature controlled valve significantly reduces energy consumption by preventing siphoning of hot water out of hot water lines during cold water use.

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