How many degrees does hot water temp drop through pex?

[Stapp]

If the gas tankless water heater is set at 125 degrees and the hot water runs through 200' of 3/4" pex and 10' of 1/2" pex before it gets to the faucet, what temperature would you expect at the faucet?

The temperature in the attic where the hot pex line is routed is 80 degrees. There are some 1/2" branches that route to other faucets along the way.

How long would it take for max temp hot water to get to the faucet from the tankless?

Would I expect hot water within a few seconds at the faucet if there is a recirculation line/pump installed?

Thanks in advance

 

[Stapp]

and the faucet says it's a 1.2gpm max flow rate.

 

[frodo]

if you have a circ line
like this


then the main will be within a degree or 2 of what your setting at the heater is

the branch going to the fixture will take a few seconds to get hot

if you want instantaneous hot water go with the under the counter pump

 

[Stapp]

if you have a circ line
like this
View attachment 14789

then the main will be within a degree or 2 of what your setting at the heater is

the branch going to the fixture will take a few seconds to get hot

if you want instantaneous hot water go with the under the counter pump

That's what I suspected, I for sure have a problem somewhere. It's taking 10-15 seconds for it to get lukewarm and then it slowly warms up from there. It takes a minute to get semi hot and then it's still 15 degrees below the tankless output temp. The output temp at the water heater was supposedly 127 degrees when I tested today.

This is new construction, brand new everything. Could bad cartridges inside single thermostatic handle shower valves be causing some sort of crossover?

Even if there was 200ft of 3/4" pex with a 10' branch to the faucet, it still should not take very long with a proper recirculation system correct?

 

[frodo]

what is controlling the circ pump on your system?
if it is an aqua stat, your problem could be a simple temp control adjustment

any temp control attached to the piping needs to be a minimum of 5' from the water heater to register a true temp in the pipe and not the temp in the tank

temp drop can also be attributed to how the piping is run,
is it insulated? the line needs to be insulated to maintain temp

I control my circ pump by running a wire from the pump to the light switch in the bathroom
that way I only circ the water when I enter the bathroom, saves on the light bill and wear on the pump

Could bad cartridges inside single thermostatic handle shower valves be causing some sort of crossover? yes

but, you need to know the piping configuration. all kinds of variables involved

post a picture of the circ pump piping at the heater