Tankless models don’t store hot water. When hot water is needed, water flows through the device and the flow sensor fires
the burner. Water lines around the heat exchanger warm the water to the desired temperature. When the hot-water valve is closed,
the flow sensor turns off the burner. (The flow must be fast enough, typically a half-gallon per minute, to turn on the sensor.)
Capacity is expressed in gallons per minute.
Hot water to faucet
Posted: September 2008 — Consumer Reports Magazine issue: October 2008