The removal of fully combusted material, ash, is removed via a water filled drag chain conveyor placed beneath the furnace. The water serves several purposes. Primarily the immediate cooling of hot ash as it leaves the furnace. This ensures safe disposal of ash, and ease of handling. This greatly increases the life of the conveyor and metal surfaces. The water also acts as an airlock at the base of the ash hoppers, preventing any extra draft of ambient air into the furnace. Therefore all air entering the furnace is controlled, with no unwanted additional combustion air.