U.S Boiler Company, Lancaster, Pennsylvania, introduces the Citadel and Citadel XL, its all-new condensing boilers and volume water heaters. The Citadel is available in five capacities (399 – 1,000 MBH) and the Citadel XL is available in 1,250 and 1,500 MBH capacities. AHRI-certified and rated up to 97 per cent thermal efficiency (98 per cent for water heater), the Citadel is available in natural gas or propane configuration.