Turn on demand gas hot water heater to 140 degrees
 

and got nice 120 degree water at the shower, all the way on hot!

much nicer in the morning

We set ours at 135 and it's decent enough. Almost no wait time. The default of 120 degrees is nuts. Would have to wait 5 minutes to shower.

Always start shower with super cold water, by the time warm water comes, I am done. Warm to hot water doesn’t do any favors to skin.

I increased the max water temperature, as others have done, because I wanted hotter water.

I have not noticed that having any effect on wait time however. Some people have said their wait time is shorter. I wonder why that would be. It should be set by the water pressure and the along-the-pipe distance from the heater to the shower head.

Is it just psychological or is the hot water wait time actually reduced if you increase the hot water temperature.

Might depend on how well the pipe is insulated - with hotter water heating up the pipe more quickly whereas cooler water would continue to lose heat to the pipe for longer

I actually compared mine when I bumped it from 120 to 135 based on the advice of a retired plumber that lives on my street. I was skeptical, so I wanted numbers to validate that it actually did anything.

I don't remember the exact numbers but it was around 60 seconds to warm up previously on an average day. Now it's closer to 30 seconds to hit maximum heat. This is for my master bedroom shower which is at the opposite end of the house from the on demand water heater.

I can get it to heat up even faster if I run the master bathroom hot taps at the same time.

I'm pretty sure that if you set them higher than 120 you void your warranty so if your heater is still under warranty, be careful. There's a reason they don't advise anything hotter than 120. I found that by turning on the shower before getting undressed it is fully hot by the time I get in it.

From my waranty:

Damages, malfunctions or failures caused by operating the unit at water temperatures exceeding the maximum setting of the operating, or high limit, control.

I would rather void my warranty and pay $900 for a new unit at an undetermined point in the future than deal with spending an extra minute standing around half naked everyday to avoid a cold shower for the rest of my life.

I would just set it back to 120 if anything happened anyways.

I'm reading this and you do understand that the temperature of the water differs on the preference of the person and if it's an issue of wait time turn the water on and brush your teeth.

Got ours set at 130. Makes a big difference

Thanks for this tip!

just wondering the exact same thing!

by laws of physics, the wait time would be longer with a lower temperature, due the heat loss in the foundation heat sink, think relative temperature for foundation absorption

Watching homes being built near us, I never seen any of them put insulation on the hot water pipes. I guess that would cost them some of their profit.

Same here, a 120 setting results in a hot water temp of 105 in the master bath.

Removing the flow restrictor in the shower head helps get it there faster also ;-)

Have you seen homes built elsewhere with insulation on the hot water pipes? I have not seen that in the homes I have occupied in NY, WA, or MD. (though to be fair, those would all now be considered older homes)

What type of shower control do you have? Is it like most hotels where you adjust the temperature by turning the lever farther or is it like the one I have where you set the hot/cold mixture once and the main control simply turns the water on and off? With the set-once, hot/cold mixture control a higher temperature might result in a longer wait time due to a lower hot water flow. It would be interesting to try this if I had an instant hot water system.

Underground piping is not insulated. The insulation would soak up water and become useless. And you wouldn't want insulation inside your concrete foundation. Greed not involved.

Thousands of gallons wasted daily
 

Inconvenient for sure but the water wasted down the drain daily is huge when multiplied by 1,000s daily.

Depends on how far your hot water tank is from your shower. Mines outside the garage. I turn on both hot water sinks in the bathroom to get it in quicker.

Okay I get it now. If your pipes are cold, the hot water wait time is not set by the time is takes for hot water to flow from the heater to the shower. The first hot water to reach the shower is not hot anymore because the thermal energy is used up heating up the pipes. So not until the pipes warm up is the water at the shower actually hot. This process is quickened by increasing the initial temperature of the water.

Interesting, I may need to increase my temperature a little more. I have it at 125 right now.

Problem with setting a high temp for an on-demand heater is the heater's minimum flow rate specification. Mine has a 0.7 gal/min minimum to keep running. With many shower heads that is more than half the flow rate. If you set the heater at 140 and mix with cold to get a 110 or so temp out of the shower head, that brings you very close to the minimum flow rate for the water heater. You may end up having the heater shut off, resulting in an all-cold shower.

Same here the first winter I started showering in my master bath and the water just never got to 120 degrees. I upped it to 130 and now it is just right on these cold days!

The water in the line between your hot water heater and your shower will get cold. Once your hot water starts to move to your shower, it has to flush the cold out, so thats why is takes minutes to get hot water to your shower.
The only I mean only reasons why you might realize it takes shorter time to get hotter water to your shower are:
1) at a higher temperature, the water in the pipes will take longer to get cold, so if you use the bath or shower within a short period of time then you will experience hotter water sooner. But if wait over night, 150/130/120 degree water will take the same amount of time to get hot water to your destination faucet,
2) you have a recirculating pump
3) at the same time you changed your shower head or strainers to restrict the water less. I put new a new shower head that has much better flow and I cut down the wait time in half or more. Same for ach faucet flow restriction screens, I got 10x more pressure and quicker heat times after doing this

My hot water is fine at 125

Instructions for raising Rheem max temp
 

Search for instructions on how to bypass factory settings of 120° on YouTube

You need to price out the on demand systems and find out what they cost installed. I will be bet they are way more than $900.. I put one in a previous home and it was around $3000 back 15 or more years ago.

Not sure changing the temp does anything, but if it works...

The higher the demand for hot water, the faster it heats. Running only the shower it will take about 2 -2.5 min to get hot water. If you turn on both hot faucets and the shower you get hot water in 30 seconds because then the heater shifts into high demand/high heat mode. The sink faucets run at about 1 gal per minute. So worst case, you're using 1.5 gallons to get hot water. So turn on the faucets and by the time you get in your birthday suit, you have hot water.

Removing flow restrictors probably has a similar effect, creating higher demand, higher heat mode. Not sure what effect it has on the water usage.

How do you guys get it to go above 120?

My controller in the Garage wont let me set it higher than 120

Never mind just found answer!

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