Unlisted food service hot plates and griddles shall be installed with a horizontal clearance from combustible material of not less than 18 inches (460 mm). Unlisted gas food service counter appliances, including coffee brewers and urns, waffle bakers, and hot water immersion sterilizers, shall be installed with a horizontal clearance from combustible material of not less than 12 inches (300 mm). Unlisted food and dish warmers shall be installed with a horizontal clearance from combustible material of not less than 6 inches (150 mm).