120 - but, my last house we had it set to 110.

103°F to 105°F (mine adjusts in 1°F increments) is my "normal" setting, for showering. I raise it temporarily as needed for other tasks (laundry, the occasional instance of hand dishwashing, or for a soak in my whirlpool tub). It automatically drops back to the normal setpoint after 30 mins (adjustable to 15, 30, 45, or 60 mins).

Tankless is most efficient when the setpoint is at the exact temperature needed for a given hot water task, and only the hot water tap is run. Tankless will produce water heated to the target temperature for as
long as 1) the unit is functional, and 2) the energy source is
maintained. There's no need to overheat the water to gain reserve capacity as is done with a traditional tank unit, and temper it by adding cold at the usage point. That's similar to floorboarding your car's accelerator and using the brake to maintain 30 MPH.

My (electric) tankless is in a broom closet in my laundry room behind my kitchen, easily accessible for adjustment. Many units support remote control panels to facilitate adjustments when the heater is installed in a location that's not easily accessible such an attic or outdoors.

125.

I dont think it uses appreciably more propane.

120 here - but 125 wouldn't use appreciably more propane other than hotter water going down the drain.

Good points about thinking differently because it is tankless. I think the temp of the hot water is a psychological thing because I am used to having closer to 130 degrees and then tempering with cold water unless I was using gloves for dishwashing.

So no one has seen issues with effectiveness of your dishwasher? I have a new Kitchen Aid and I don't think it heats the water it uses. I always run hot water to the sink before turning on the dishwasher.

Ours is set on 130. I tested it for a while and 130 was the only temp it would pull hot enough for me. Our gas bill did not go up anything noticeable.

When we size tankless the design temp for the shower is 105 - much higher than that it's just too hot. I think some people are seeing excessive heat loss in their pipes (say, for example uninsulated pipes in a slab or a long run to the master bath).

I believe that most dishwashers boost the water temp. The risk of scalding is way too high to set the water temp based on the dishwasher - and dishwasher manufacturers know that and have improved their design.

In general there's no benefit to raising the temp beyond what's comfortable in the shower - once you have it high enough to mix a little cold water in to allow for personal preference. There can be an issue though with setting it too hot.

Tankless heaters have a minimum flow rate under which they will shut off. If you set the temp too high, then someone washing their hands or taking a cool shower will have the heater shut off completely because there aren't enough GPM flowing through the heater to keep it on. Something to look for when choosing a tankless is the minimum flow rate to activate it and keep it running - lower is better. Rheem units have had some of the lowest activation rates (0.4 gpm) and minimum flow rates to keep it running (0.26 gpm).

My dishwasher (a Fisher & Paykel DishDrawer) heats the main wash and final rinse to specific temps per the selected cycle, extending the cycle time as necessary to reach the target. It can work on a cold supply, although is not connected as such.

Most modern decent dishwashers boost the temp. But agree, the temp won't make that much of a difference in energy use.

I have a navien and it is set at 125. 120 was just not cutting it for us. I know that 5 degrees seems negligible, but it really made a difference. Heater is in the basement and two showers are on the third floor, so it’s a long way to travel. I also adjusted the shower mixers so more hot water could come through. Now my only problem is the Delta kitchen faucet that won’t allow it to go above 105...I feel like it’s not hot enough to clean up, but maybe that’s just me.

"By the time the water gets to the various faucets in the house, the water temp is more like 115 - 117 degrees. .. but the water temp just feels a bit chilly to me. "

Did you measure a 117 degree water temperature at the faucet? Most people could not tolerate a 117 degrees on their skin. I am surprised you say this feels chilly.

Most dishwashers do an initial rinse to remove the large food particles off the dishes. I think running the hot water before starting the cycle wastes water and energy. I never run the water and the dishes come out spotless.

If the dishwasher has a sanitize cycle, then it must heat the water to about 175 degrees. Dishwashers are now designed to run long cycles with little water. I would think the water has to be heated in order to run these long cycles. If not the water would be cold by the time the cycle has ended.

"I think running the hot water before starting the cycle wastes water and energy. I never run the water and the dishes come out spotless."

Agreed - besides, If you have a manifold system it doesn't matter anyway.

There are generally a couple of short duration rinses at first to help heat up the pipes and the dishes, and clear off the food, before the main cycle starts.

Mine is at 130.

The one thing about tankless you need to remember is that a level of flow must be maintained in order for the unit to 'fire up'. Drop below that flow and it shuts off. This can be an issue when showering when you mix hot and cold together, resulting in a slug of cold water hitting you at an un-opportune moment. This is why some turn the temperature down and use hot only in the shower.

mike_home, my choice of words was poor! The water doesn't seem chilly - I should have said it doesn't feel very hot. I can hold my fingers in the stream for several seconds without discomfort. I did measure the temp by continuously running the water in a bowl for over two minutes and testing with my Thermapen.

The comments about dishwashers makes sense. I couldn't find documentation in the users manual so I contacted Kitchen Aid via chat. The reply:

"The dishwasher would pause during the cycle for short periods of time to raise the water temperature if it senses that the water temperature has dropped. It will not heat cold water from the the start. The dishwasher will need to be connected to a hot water supply."

I've not had any issues with my dishes not being cleaned but we haven't been in the house long enough to put it through demanding loads.

I think I will leave the temp setting as is. Comments in this thread have helped me understand how to think about tankless water heater usage. Thanks to all who replied!

"mike_home: Dishwashers are now designed to run long cycles with little water. I
would think the water has to be heated in order to run these long
cycles."

Perhaps you'll be surprised to learn that some units (recent Whirlpool and KitchenAid models come to mind) may maintain low as 105°F for the wash period on the designated "normal" cycle without any high-heat options added. The final rinse typically is heated to a higher temp to promote water evaporation for drying. Dishwasher detergents nowadays are enzyme-based and formulated to perform at lower temperatures and long wash times vs. "old" formulations that contained chlorine bleach and needed scalding-hot temperatures when cycle times were much shorter and energy usage was not so much a concern.

nanj, if the hot water is too hot to touch then why the need to make it hotter? Tempering it with cold water is wasting energy and water.

If you had a hot water tank, then going below 120 F degrees raises the risk of Legionnaire's disease. You don't have this issue with a tankless system.

I bought a Bosch 800 series dishwasher about a year ago. The manual lists temperature by wash cycle. The normal cycle uses 113-131 degrees for washing and 156 for rinse. For heavy duty it is 151-160 for wash and 162 for rinse. Wash times are based on 120 degree water supply. If the temperature is lower then the cycle may be longer.

dadoes

I know my 3 year old Frigidaire (mid range) does heat the water during most cycles (it boost/maintains - doesn't heat from cold) I know this because it was defective from the factory and wasn't providing any heat - I went through troubleshooting including a temp probe during the cycles and also looking at the cycle diagrams in the troubleshooting manual.

I can also tell you without that additional heat it really sucks at dish washing.

A new computer module fixed things right up - and I can also tell you that "Proudly Inspected by 32" didn't do his/her job.