Suspended-type unit heaters shall comply with the following requirements:
1. A listed unit heater shall be installed with clearances from combustible material of not less than 18 inches (460 mm) at the sides, 12 inches (300 mm) at the bottom and 6 inches (150 mm) above the top where the unit heater has an internal draft hood, or 1 inch (25 mm) above the top of the sloping side of a vertical draft hood. A unit heater listed for reduced clearances shall be installed in accordance with its listing and the manufacturer's instructions.
2. Clearances for servicing shall be in accordance with the manufacturers' recommendations contained in the installation instructions.