The XL series is offered in two standard configurations, vertical and horizontal. Vertical configurations support capacities ranging from 37.8 to 63.0 MMBTU, and horizontal configurations support capacities from 67.2 to 92.4 MMBTU. The standard and low-NOx vertical and horizontal configurations are capable of burning natural gas, propane gas, air-atomized #2 oil, as well as combination gas/#2 oil. Full modulation operation is standard, and a parallel positioning system is required for burner management and combustion control.