U.S. Boiler announced its new Citadel and Citadel XL condensing boilers and volume water heaters. The Citadel is available in five capacities (399 - 1000 MBH) and the Citadel XL is available in 1250 and 1500 MBH capacities. AHRI-certified and rated up to 97% thermal efficiency (98% for water heater), the Citadel is available in either a natural gas or propane configuration. The Citadel can be stacked two-high without the need for accessory racking systems, while the Citadel XL can be stacked with a rack system. Zero side and top clearance optimizes the amount of Btu that can offer per square foot. Included at no additional cost are the low water cutoff and high and low gas pressure switch making the boilers CSD-1 compliant. A standard, reinforced 3-in-1 vent connector facilitates the use of polypropylene, CPVC or stainless steel venting on the Citadel. Venting of up to 300 equivalent feet (combined) of vent in AL29-4C, polypropylene or CPVC is acceptable. Modbus communication also comes standard.