Abstract: A system for under-cart cooling of furnace carts in tunnel furnaces comprises a plurality of closed cooling air channels which fill the under-cart channel to the largest possible extent and are only slightly spaced from the undersides of the tent and are only slightly spaced from the undersides of the furnace carts. The cooling air channels which are streamed through by cooling air provide for sufficient cooling of the furnace carts, while simultaneously an exchange of cooling air from the under-cart channel and of hot air from the burning channel can be avoided in a simple manner so that there is no need for additional sealing arrangements.