Gas heater
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.  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.