if default then
	function default.get_furnace_active_formspec(fuel_percent, item_percent)
		local formspec = "list[context;src;0,0;1,1]" ..
				"list[context;fuel;1.25,0;1,1]" ..
				"list[context;dst;5,0;4,1]"
		return sparktech.add_inventory(8,1.4,formspec)
	end
	default.get_furnace_inactive_formspec = default.get_furnace_active_formspec
end