A demand pump is one solution to the problem of having hot water without a long wait and without wasting water because cold water is running down the drain as hot water is drawn from the water heater.
It consists of a pump at the point of use, such as in a bathroom, and a switch. When users want hot water, they turn on the pump, which then pulls hot water from the water heater through the lines and may push cold water into the cold line to keep it from being wasted. After a minute or two, the user can bathe or whatever.
Demand pumps not only save water. They also save energy, since the other typical solution, the recirculation system, has hot water circulating all the time and heat is radiating away through the pipes all the time, too.
Two examples of demands pumps are the Metlund D'MAND and Chilipepper.
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