Alternatives to furnaces include ganister, boilers, limekilns, FIERY, KILNS, and heatpumps. Ganister is a type of sandstone used as a building material, while boilers are devices that use combustion to heat water or other fluids. Limekilns are structures used to produce lime from limestone, and FIERY is a type of fuel made from coal dust and clay. KILNS are ovens used to bake clay and other materials, and heatpumps are devices that transfer heat from one area to another.