A tankless gas water heater works by heating water on demand. The unit sits on idle, until the hot water tap is opened inside your home, and then the cold water flows into the water heater.
The water flow is detected by a sensor that ignites the gas burner, to heat the water in the heat exchanger.
As the cold water flows through the gas water heaters it typically follows a serpentine pattern through the heat exchanger, absorbing as much heat as possible. The speed with which the water travels through the gas water heater determines the speed of hot water delivered (flow rate).
The faster the water travels through the unit, the lower the temperature output will be, and the slower the water travel, the higher the temperature output will be.
An electronic control unit modulates the gas burner to maintain a set water temperature.
The hot water then exits the gas water heater and travels directly to the tap or appliance, not to a storage tank.
When the hot water tap is turned off, the heater shuts down. Your gas water heater will deliver unlimited hot water, unless the power and gas supply is interrupted.