i like the illustrations! looks like one of them can support the not within 12" opinion. the others clearly support the wording in the code. the written word of the code trumps the picture book in the code enforcement business. the code officials can interpret info and make an alternate decision based on the written word. this is like barbequing beans=some fall thru the grill. i would not lose sleep over minor erroes. the purpose of the upper opening is to ventilate heat build up from the appliance enclosure.as the air surrounding the equipment is heated,it rises to the top of the enclosure and is at a slightly higher pressure. unless the pressure is relieved, it will continue to build and can prevent the inward flow of combustion air to the lower opening, thus witin 12" of the top and bottom. i am new here and appreciate the sharp minds and spirited debates! fun place!