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What are the two types of systems that work with existing hot water storage tanks?

  1. Hot Water Demand System (electrical pump system)
    The Hot Water Demand system (HWDS) is an electric water pumping system that quickly (typically within 30 seconds) brings hot water to the fixture by drawing water from the hot water tank and returning cooler water to the hot water tank where it is reheated. The HWDS is usually installed under the sink farthest from the water heater. At the push of a button, it circulates the water normally discarded down the drain back to the water heater through the cold water line. Simultaneously, the HWDS pumps hot water from the hot water heater to the fixture. When a predetermined temperature (usually 5°F above room temperature) at the fixture is reached, the pump stops automatically and hot water is available at the faucet. The pump may be operated by a switch placed next to the fixture or by a remote control.
  2. Hot Water Valve (non-electrical)
    This is a mechanical control valve installed at the point of use. When the water in your hot water pipe and the control valve cools below about 85 degrees F (user adjustable), the thermal materials within the control valve contract, and silently open the valve. Thermal convection naturally circulates the cooled water through your existing cold water pipes and back to the hot water tank for reheating. Your existing hot water tank now uses less energy reheating 85 degree F water instead of cold ground temperature water. When hot water reaches the control valve, the valve automatically closes. This maintains hot water at the control valve without wasting water or energy. When you mount the hot water control valve in the fixture furthest from your hot water tank all other fixtures in your house also benefit. No electricity is necessary. Note: Circulation of water by thermal convection must not be restricted (no check-valves) between the hot water tank and the control valve.