To improve the efficiency of a steam boiler system which generates 600 psia steam for refinery process use, the boiler feed water (BFW) is to be preheated to 400 degrees F from 100 degrees F before it enters the boiler. This preheat will be accomplished by installing a heat transfer coil in the boiler flue gas stack, recovering heat energy that would otherwise be exhausted to the atmosphere. This BFW is a "compressed liquid water." How much heat energy, experssed as MBTU/hr., is required to effect this BFW preheat at 75 gal./min. BFW rate? This value is needed to design the heat transfer coil.