The American Heat AH SERIES electric tankless water heater is a marvel of technology and engineering - overflowing with technology yet packaged in an intelligent,simple design. It heats water entirely on demand, only when it is needed. When a hot water faucet is turned on and the water begins to flow, a sophisticated flow sensor detects that hot water is being demanded and turns the water heater on. Instantaneously, a series of sensors gather information about the flow rate of the water and the incoming water temperature. This information is sent to a microprocessor which calculates the amount of power needed to heat the water to the temperature set point. The water flows across the internal heating elements and exits the unit at the desired temperature. The start-up process takes a couple of seconds. A convenient thermostatic control and digital display on the front of the unit allows the homeowner to select an output temperature of between 80°F and 125°F.