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In natural gas furnaces, water heaters, and room heating systems, a safety cut-off switch is normally included so that the gas supply to the pilot and heating system is shut off by an electrically operated valve if the pilot light goes out. This cut-off switch usually detects the pilot light in one of several ways: A flame rectification device. [2]
A condensing gas furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. The primary gain in efficiency for a condensing gas furnace, as compared to a mid-efficiency forced-air or forced-draft furnace, is the capture of latent heat from the exhaust gases in the secondary heat exchanger.
The water is blown out of the boiler with some force by steam pressure within the boiler. Bottom blowdown used with early boilers caused abrupt downward adjustment of boiler water level and was customarily expelled downward to avoid the safety hazard of showering hot water on nearby individuals.
Early hot water systems were used in Ancient Rome for heating the Thermæ. [13] Another early hot water system was developed in Russia for central heating of the Summer Palace (1710–1714) of Peter the Great in Saint Petersburg. Slightly later, in 1716, came the first use of water in Sweden to distribute heating in buildings.
Non-flued heaters can be risky if appropriate safety procedures are not followed. There must be adequate ventilation, they must be kept clean, and they should always be switched off before sleeping. If operating correctly, the main emissions of a non-flued gas heater are water vapour, carbon dioxide, and nitrogen dioxide.
Each room has an outlet from the duct system, often mounted in the floor or low on the wall – some rooms will also have an opening into the cold air return duct. Depending on the age of the system, forced-air gas furnaces use either a pilot light or a solid-state ignition system (spark or hot surface ignition) to light the natural gas burner. [3]
A Single-Pole, Single-Throw (SPST) mercury switch on millimetre graph paper, device length approximately 1.5 cm Another mercury switch design. A mercury switch is an electrical switch that opens and closes a circuit when a small amount of the liquid metal mercury connects metal electrodes to close the circuit.
A high pressure watertube boiler [1] (also spelled water-tube and water tube) is a type of boiler in which water circulates in tubes heated externally by fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-generating tubes.