A "closed system" means a system of combustion and fuels or raw materials that are designed to have a volume control, weather and environmental conditions in combustion, such as cement pots, boilers, etc.
"Closed system" means that the ignition system and fuel or raw materials that are designed to control air volume and the environment in burning kilns, such as radiators.
"Closed system" means the combustion system, fuel and raw materials to control or design air volume and the environment in combustion. Such as the burning pot, cement, radiator, etc.