My shower runs out of hot water quickly. Initially the water is perfectly hot, then it starts cooling after a minute or so and we need to adjust the lever to maintain the temperature. Somewhere around 10mins (give or take) you're pretty much out of hot water. I've tested this in our other shower as well, same issue.
To troubleshoot, we bought a new Rheem 50 Gal Gas WH as the previous was 12yrs old. Its only my wife and I in the house and we never shower at the same time in different showers.
There is no mixing valve in my setup as far as I can see, I've traced the hot water pipe from the WH to where it exits the basement.
To troubleshoot, I've been in the shower, waited for the water to start cooling, then ran downstairs to run the kitchen sink hot water and the water was noticeably cooler as well, similar to what I was getting in the shower.
Any ideas? New WH(same issue present w/ old WH), no mixing valve, water heater is set to a notch (or 2) above the default setting.
I have an HVAC friend as well as an HVAC uncle whos been in business for a while and he doesnt have a definitive answer either.
The basement is heated, so its usually about 68F-70F.