What is Gas heater?
[[File:Gas heater 1970s.jpg|thumb|200px|right|Upright non-flued [[liquefied petroleum gas]] heater, 1970s]] [[File:Wall heater.jpg|thumb|A wall mounted gas heater that runs on either [[propane]] or [[natural gas]].]] A '''gas heater''' is a [[heater]] used to heat a room or outside area by burning [[natural gas]], [[liquefied petroleum gas]], [[propane]], or [[butane]]. ==Operation== A gas heater controls its cycle by using a mechanical or electronic [[thermostat]]. Gas flow is turned on with a valve. The gas is lit by an electric filament or [[pilot light]]. Flames heat a [[radiator]] in the air duct, [[convection]] or a fan may distribute the heat to the room. ==Non-flued heaters== [[File:Gas Heater of 2000s.jpg|thumbnail|right|Non-flued gas heater, running on [[natural gas]].]] Non-flued heaters – also known as '''unvented heaters''', '''vent-free heaters,''' or '''flueless fires,''' are either permanently installed or can be moved around, and sometimes will have a [[catalytic converter]]. <ref>{{Cite web|url=https://www.hse.gov.uk/research/rrhtm/rr023.htm|title=RR023 - Flueless gas fires - concentration of carbon monoxid...|website=www.hse.gov.uk}}</ref> Non-flued heaters can be not safe if safety rules are not followed. There must be enough [[ventilation]] and they must be kept clean. They should always be switched off before sleeping. If they are operating correctly then the main emissions of a non-flued gas heater are [[water vapor]], [[carbon dioxide]], and [[nitrogen dioxide]]. ==Flued heaters== [[File:Good woodburning stove.jpg|thumb|A flued heater that burns wood for heat. Any [[byproduct|byproducts]] will leave through the flue pipe in the back of it.]] Flued heaters are permanently installed wherever they are placed. The [[flue]], if properly installed correctly should remove all of the heater emissions. A correctly operating flued gas heater is safe for use. Not all flued heaters are allowed for use in indoor living spaces. Some flued gas heaters can be used indoors, but not where people eat