Someone comfortable at 102 o would be very uncomfortable at 104 o . Federal Law limits Jacuzzi and Spa heaters to 104 o . Dishes - Dishwashers normally have their own internal heating elements. It is not the temperature of the water but the combination of the hot water and the soap that kills germs. Clothes - Clothing is normally washed in cold or warm water.
Hot water causes clothing to shrink and fade.
What to expect Tankless water heaters do not work in the same way as a conventional water heater. The only reason a conventional water heater 'superheats' water to 120 o -140 o is so that the limited volume of water they hold can be extended by mixing it with cold water. Not only does this waste energy by heating the water and then cooling it again, but it increases the possibility that a child or elderly family member will scald themselves accidentally. The process of 'superheating' the water is not necessary with a tankless water heater because it produces an unlimited supply of hot water. We suggest that when a tankless water heater is installed it is adjusted so that those who like the hottest shower in the home are comfortable with the mixing valve be set to maximum hot.