A hot water recirculation system is a plumbing system that moves hot water to fixtures quickly for faster hot water so there is no need to wait for the water to get hot. Rather than hot water cooling (common in most water lines), recirculating systems circulate the water between the water heater and fixtures providing instant hot water when you want it.
- dedicated loop: The hot water pipe is installed in a loop throughout the home, passing near each plumbing fixture. At each fixture, a short pipe connects the loop to the hot water valve. Because hot water is constantly circulating through the hot water loop, any time a valve is opened, it takes only a fraction of a second for hot water to reach the valve.
- integrated loop: This system is typically used on retrofits but may also be installed on new construction. It consists of a temperature controlled thermal convection powered hot water recirculation valve installed under the plumbing fixture farthest from the water heater. The system contains a sensor which opens the valve when the water temperature drops below the adjustable temperature setting.
In this system, hot water is re-circulated intermittently. Hot water is returned to the water heater via the cold water pipes. This raises the temperature of the cold water slightly, but it returns to the usual cold temperature in a short time.
Do they really save energy and water?
Regardless of whether they are controlled manually or automatically, recirculation systems reduce the amount of water that goes down the drain while the homeowner waits for the desired temperature. This fact allows for the following three advantages over conventional water distribution systems:
- They save time. Recirculating systems deliver hot water to faucets quickly, adding convenience for the homeowner.
- They conserve water. According to statistics from the U.S. Department of Energy and the U.S. Census Bureau, between 400 billion and 1.3 trillion gallons of water (or close to 2 million Olympic-sized swimming pools) are wasted nationally by households per year while waiting for water to heat up.
- They limit municipal energy waste. The DOE estimates that 800 to 1,600 kilowatt-hours per year are used to treat and pump the water to households that will eventually be wasted while the occupant waits for tap water to warm to the desired temperature.
If recirculation systems (using electrical pumps) operate continuously they have the potential to use significantly more energy. For a modest-sized pump, this might be 400 to 800 KWH a year if the pump runs all the time. Also, heat loss from the pipes can be significant if the hot water pipes are poorly insulated. However, substantial energy can often be saved by reheating the already pre-warmed (re-circulated) water instead of heating cold ground temperature water (which would normally be supplied to your water heater without a recirculation system).
Some jurisdictions, particularly in areas where water is scarce, offer rebates on the purchase and installation of hot water recirculation systems. The cities of Santa Fe and Albuquerque, New Mexico, for instance, offer a $100 rebate for homeowners who purchase a hot water recirculation system. The city of Scottsdale, Arizona, offers up to $200 for residential property owners who install theses systems.
Availability and Cost
Hot water recirculation systems are available nationwide from manufacturers, distributors, plumbing wholesale supply warehouses, and at selected retail home stores. The initial cost of dedicated systems may prevent some homeowners from installing these systems, as they require the purchase and installation of a pump and a large amount of piping. Integrated systems, by contrast, are less costly and much easier to install. Energy savings will vary, depending on the design of the plumbing system, method of control and operation, and homeowner use.
Dedicated return line systems require an in-line air valve and shut-off valve. Other requirements will vary with the installation’s configuration, but may include a check valve and an additional shut-off valve. The pump may be connected to a timer so that the pump circulates water through the loop only at desired times (which limits instant hot water comfort and water savings). Inspections should be limited to the system’s proper operation.
Hot water redistribution systems are innovative plumbing systems that can save water and energy in most circumstances.