Hot water outlet: 3/4 to 1/2 switch-over. How soon?

The inlet of tankless water heater (Rinnai 2532 FFU-C, NG) is piped with 3/4 copper through. The 3/4 outlet (hot water) needs to be switched over to 1/2 somewhere below the isolation / pressure valves. The hot water runs are relatively short (the closest to WH shower is ~5' away). Most convenient for me would be to change-over to 1/2 copper after just 5"-6" of the 3/4 vertical run. Is that acceptable? Cons/Pros? UPC? Thanks :-)
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1/2" ought to be able to supply all the water you need.
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Thanks for your answer. I am concerned with sustaining the volume (GPM) through the WH (WH may not work properly if the volume is too low). I am trying to uderstand the relationship between the outlet's parameters (ID, length before it is downgraded from 3/4 to 1/2) and the volume of water flowing through the WH. It seems that the larger outlet would have larger volume capacity. Theoretically that is. What are the practical implications? Will that benefit (impede less) the GPM)? I am guessing it will not, but would like to hear other opinions. Thanks!
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Why are you choosing a tankless?
First they cost so much more than a standard tank the energy payback exceeds the probable life of the heater:(
You MAY need to upgade your electric service, if the tankless is electric, or your gas service, tankless consume LOTS when they are on..
In the winter a standard tanks heat loss goes to help heat the building, so its not really lost, this probably cuts your energy saving by 1/2 kinda dependent on local temperatures.
good your aware low flow may result in cold water, like washing hands....or using a spray wand on dishes.
exceeed max flow and cool shower is result.
Of course the UNLIMITED hot water may result in longer showers ultimately consuming more water sewer and heating fuel....
People who have owned a tankless say there are two great days.............
the day its installed and the day its replaced by a standard tank........
so why are you buyng a tankless?
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The piping is not going to affect the flow through the heater, but the end outlet will. If you look at the tubing connecting to the faucets, it is smaller yet so 1/2" will supply all of your needs. If, however, you open two or three faucets full blast, then the 1/2" tubing can become the deciding factor for flow. You have to compare openings to the areas of the tubing ID. Then there is friction loss along the way.
In any case, the WH is temperature dependent, not flow dependent. If the flow is low it will not make any difference. If the flow is above the ability of the heating systems,, then it will be noticed.
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Edwin Pawlowski:
Thank you for answering my question directly :-)
al
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