We have a tankless water heater.
I want to set the temperature so that it is the most energy efficient. Should I set the temperature of the water so that it is just hot enough for taking a shower?
I figured that if it is set that way then when I take a shower all I have to do is to turn on the hot water and would not require any cold water to bring it down to a comfortable temperature.
Am I overlooking something here?
I guess our laundry washer would also have hot enough water. The dishwasher should be fine too, yes?
Currently we have it set to 120 and it is hit enough. We still have to fix some cold water with it.
Best Answer
Setting the temperature lower would be the most energy efficient setting, but the question is open whether this would be a significant savings. It may be beneficial to the heater--IIRC the instructions for my Bosch Aquastar 125B say that if the heater is set at the lowest flame setting then it may never have to be descaled.
The downside of outputting a lower temperature of water is that this will reduce the ability to supply multiple simultaneous uses.
But there is the question of microbes in the water and specifically Legionella, the cause of Legionnaires' disease. All over the scientifically based world the recommendation is that water stored in tanks should be kept cold or at a temp of 130 to 140 F, not in between. It is not clear how this applies to hot water supply systems that use a tankless heater.
If all the water that ends up abandoned in the hot water pipes after the hot water taps are turned off has been heated to 140 F, then that would have killed "all" the Legionella in the incoming water. As it sits in the hot water line and gets tepid there is not enough surviving bacteria to grow to a dangerous level. But if the heater never heats the water past say 105 F, then Legionella will survive to grow in the hot water supply lines.