Hot Water Test Data (Prelim.) was taken to test the heating effectiveness of the exchanger and recirculation pump. The graph plots the approximate temperature of the water in the tub over time in minutes. The water in the tub and in the boiler was initially 56 degrees F. At 25 minutes, 1 gallon of water was added to the 1 gallon in the tub to determine the recovery time after water is added.