pressure to keep the gas valve open. If the pilot fails, the valve closes. To restart the system, the valve must be held open manually and the pilot lit, and then the valve must be held open until the element heats up enough to hold the valve open. Non-electrical schemes are appropriate for systems that do not use electricity. The above methods are examples of the use of "fail-safe" safety protection. Energy waste In domestic heating systems with pilot lights it has been estimated that half of the total energy usage is from the pilot light, with each pilot light on average using between 70 and 500 watts of gas power (between 8 and 16 gigajoules/year). The heat from a pilot light in many appliances (furnaces, space heaters, water heaters) is generally released in the same chamber as the primary burner. The energy loss is much smaller for pilot lights in space heaters than other products, because space heaters heat a smaller enclosed space and contribute more significantly to heating the room. The appliance efficiency of a gas fired balanced flue local space heater in pilot light mode is almost equal with the appliance efficiency measured at the reduced power of the appliance, which efficiency is between 65 – 95% based on the low calorific value of the consumed gas, making part of the pilot light's energy consumption into a useful heat. Modern alternatives An alternative to the pilot light is a system to create a high voltage electrical arc or spark between two electrodes, in order to light the gas flowing to the burner. Fail-safe design for such a system requires the burner flame to be detected by passing an electric current through the flame, which is received by the flame rectification circuit inside an ignition controller connected to the gas valve. Flame rectification occurs when electrons flow through the flame burning, which the ignition controller senses and knows the flame is there, keeping the gas valve open. If the appliance loses gas or the flame goes out, the ignition controller doesn't see the flame, closing the gas valve. A red-hot surface can also be used to provide ignition. Such igniters are often made of silicon carbide, silicon nitride, or another material that is durable under prolonged exposure to extreme heat. Hot-surface igniters are commonly used in cooking ovens, boilers, and modern gas furnaces. A disadvantage to modern alternatives