Minecraft wiki entry for Dried_Kelp_Block, associated text: Dried kelp blocks can be used as fuel in furnaces, blast furnaces, and smokers. Its burning time is 200 seconds (4000 ticks), and it is able to smelt 20 items. This is 2.5 times the burn duration of coal and charcoal, and 0.25 times the burn duration of a block of coal. It is the fuel with the highest number of operations per fuel below 64 items. The highest number of items that can be smelted without any refills or hoppers and without loss of fuel is 60 items (3 dried kelp blocks).