23 55 00 Fuel-Fired Heaters
23 55 33 Fuel-Fired Unit Heaters
23 55 13 Fuel-Fired Duct Heaters 23 55 13.13 Oil-Fired Duct Heaters 23 55 13.16 Gas-Fired Duct Heaters 23 55 23 Gas-Fired Radiant Heaters 23 55 23.13 Low-Intensity Gas-Fired Radiant Heaters 23 55 23.16 High-Intensity Gas-Fired Radiant Heaters 23 55 33 Fuel-Fired Unit Heaters 23 55 33.13 Oil-Fired Unit Heaters 23 55 33.16 Gas-Fired Unit Heaters