439. If a boiler generates saturated steam at 75.3 psig, how much heat is required to change the water into steam if the feedwater temperature is 220°F

The heat required to convert feedwater at 220F to saturated steam at 75.3 psig (90.0 psia) is the difference in enthalpy, calculated as the enthalpy of saturated steam at 90.0 psia (1185.3 Btu/lb) minus the enthalpy of water at 220F (188.1 Btu/lb), resulting in 997.2 Btu/lb.