The flue system is composed of two flues, the inner flue and the outer flue. Later hall houses were built with chimneys and flues. The massive old chimneys were removed and replaced with small flues within the new walls. "Sultana" had tubular boilers filled with 24 horizontal 5-inch flues. All houses were built with marble-mantelpieced fireplaces and flues. C2 is for vaporising or atomising burners in appliances connected to flues. Another use of the term is for the internal flues of a flued boiler. Apprentices were not allowed to climb flues to extinguish fires. The space outboard of the tubes formed a pair of exhaust flues leading forwards. The rate of combustion was controlled by the flues and the ash box. It had four flues and a timber roof. Roman thermae constructed centuries ago had flues. Four flues are connected with each other, the upper chamber and the stokehold. This was a common room, warmed by flues beneath the floor. These tile flues were referred to as "caliducts".