Dear Polly: How low should one turn one's water heater thermostat for significant savings on the hot water bill?
Dear Ida: How low you go is really up to you. However, here are some guidelines:
Lowering your thermostat from 140 degrees (standard) to 110 degrees will save you 20 percent on your annual hot water bill. However, if you have a dishwasher, 110 degrees may not get your dishes as clean as you like. Many newer models of dishwasher have automatic water heaters; they usually recommend that your hot water be set at 120 degrees (the dishwasher then heats the water to 140). Lowering the thermostat further (say, to 110) may lengthen the dishwasher cycle (because the water takes longer to heat to 140) or may result in less clean dishes.