For a tankless heater, this means that there is a smaller draw of hot water at 125 degrees and a larger draw of cold water. Since the draw of hot water is reduced, the amount of gas to heat the smaller flow is also reduced.For washing dishes or laundry, the higher temperature will cost you more money as the temperature may not be offset with cold water.ince the draw of hot water is reduced, the amount of gas to heat the smaller flow is also reduced. For washing dishes or laundry, the higher temperature will cost you more money as the temperature may not be offset with cold water.