How to set hot water temperature and what's safe. 130 recommended
 

I would not set it to 140. That creates a risk of burns.

140 degrees may be unsafe but I have no choice...
 

My lovely wife REQUIRES the 140 setting! And I use a 5-gal bucket to catch several gallons of water from going down the drain. I water my lawn in "poor grass" areas.

Best to measure it at the point of use. For newer construction with tankless heater, 140 is probably below 130 after traveling from the front corner of the garage, under most of the house, to the master bath.

I would not rely on the ground to keep me safe. Measuring now will result in a different temperature than in August.

You can find them for less than $900 or more than $900. I just threw out the quote of $900 as I know my retired plumber friend just installed one for a relative and the actually Rheem on demand heater was $897 from Home Depot or something like that.

Maybe a little, water lines are less than a foot under the slab and heat transfer is slow.

My cold water temp ranges from 70 - 76 year round.

When we had out Design visit last May, adding the hot water recirculating loop was an option, for a not so small $8,500 fee. I was told all hot water lines were also insulated, in that option. Also, I would hope any lightly buried water lines are not sitting in water! Under any slab! Should be very dry under the slab.

New construction with a Rheem on demand water heater set to 120. Our master bath is the furthest from the tank. At 120, the master bath temp is marginal, at least with these winter months. Tried setting the temp higher than 120, didn’t budge. Just say a YouTube video how to bump it higher. Going to set 125 next to see how that goes. For the winter months anyhow. Don’t forget to do an annual flush on the heater. Perhaps 2-3 times a year, for those that have not installed a water filter/softner. The how to, also on YouTube. Also a good idea to keep a spare ignition for the heater on hand. As well as an A/C capacitor. Both these items are common fail items. Both are cheap enough to keep a spare, as they usually fail at the worst time. Both are easy enough to swap out via YouTube videos. You can thank me later.

good except that we run 130 out of the shower head at max temp
120 is a safety limit to prevent skin burns for sensitive skin.
I have a bunch of sun burned leather on my back

seriously, if we change the temperature higher for Jan/Feb, do you not think we can set it back for warmer/hotter months?

Of course you can. My point is this. Suggesting to people who will not think to reduce the setting in summer that they should run their heater at skin burn temperature is irresponsible.

Still insulting everyone's intelligence,

don't you think that as the ground warms with the season, that the shower head temperature will slowly increase as well, and when the increase hits the too hot for all the way on , then people will wander out to the garage and change the setting? The knob in the shower is also able to adjust temperature down. . .

please, many of us posters and typists still have working brains.

Only the people who think the shower temp is either hot or off have some issues

Does the cold water not run to your shower?

If you can set your heater to a temperature that you like to shower in with straight hot water, great! If the straight hot water is too hot for a spouse or a visitor or during the summer then add a little cold water to the mix. It has never occurred to me to try and adjust the shower temperature using the dial on the hot water heater.

I find it very easy to avoid burns by testing the water temperature before I step into the shower. I test the water at every hotel I stay in and I test the water at home. If I choose to not do that then who is to blame for any discomfort I may experience?

My water heater is behind the wall of the guest bathroom. I take my showers in the guest bathroom. I get hot water within 15 seconds. It's magnificent.