Natural gas water heaters that do not have a continuously burning flame or pilot light are said to be pilotless. This reduces the amount of energy needed by the appliance, conserving fuel and reducing emissions. The technology is limited to on-demand water heaters.
Ignition
A spark produced from an electrical current ignites the gas in a pilotless water heater. Think of it as the equivalent of the sparkplug in the car igniting the fuel mix in the engine cylinder. The electricity for the spark is from a wall outlet or from an internal generator utilizing the movement of the water through the pipes to produce electricity. In the case of an internal generator, the water heater continues to function even during an electrical blackout.
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Efficiency
The pilot light of a tankless water heater is wasted energy because it is not heating water until demand calls for it and the main burner ignites. For a storage water heater, the pilot light serves as standby heat, keeping the water warm at times of no demand. Think of it as a low burner under the teakettle that maintains a warm temperature. The burner kicks in when demand draws some of the hot water and cold water enters the tank. Once the new water reaches the thermostatically controlled temperature, the burner shuts down and the pilot light maintains the temperature in the tank. No energy saving is accrued for a pilotless storage tank type water heater.
Safety
A pilotless water heater has no continuous flame that can pose a hazard. This is important in specialized applications such as recreational vehicles.
Tankless Water Heaters
A tankless water heater, or on-demand water heater, has no storage tank. Opening a hot-water faucet creates a flow of water through the water heater. This triggers the ignition of the gas burner that heats between 1 and 5 gallons of water per minute depending on the make and model. When the flow of water through the water heater stops, the gas burner shuts down.