Details test and examination criteria for gas-fired low-intensity infrared heaters and infrared radiant tube heaters with inputs up to and including 400,000 Btu per hour (117.23 kW) per burner. These appliances are for use with natural gas, manufactured gas, mixed gas, liquefied petroleum (propane) gases and LP gas-air mixtures. These appliances may be convertible for use with natural gas and liquefied petroleum (propane) gasses, when provision is made for a simple conversion from one gas to the other. These heaters are intended for installation in and heating of outdoor spaces or nonresidential indoor spaces. Low-intensity infrared heaters and infrared radiant tube heaters may be suspended overhead, angle mounted overhead, wall mounted or floor mounted.