Repiping my master bathroom shower and sink. We have a new instant hot water heater on an addition to our house 10' away. The shower and sink now run off the water heater in garage, 100' away.
I tee'd into hot water supply line in the addition (instant hot water tank) and I am connecting the sink and shower in master bath to this new hot water line and capping the old hot water supply line from the garage (just for the master bath) which is at the end of the run. My question is can I use the cold water supply line from the house (original cold water supply) or do I need to run the cold water from the addition also. Both cold water supplies originate after the regulator coming into the main house.

  • 1
    It doesn't matter, use whichever is most convenient (seems to me that using the original supply would incur less additional pipe work). Mar 30, 2018 at 17:35
  • thanks. the original is right there so I will use that one.
    – Kevin
    Mar 31, 2018 at 0:09

1 Answer 1


Your cold water line connection if up to code is not an issue as to where it comes from. What I mean by 'if up to code' is that it was originally installed up to code.

The short answer is you need not do any other work regarding that cold line unless you really are pitching an itch to do it.

The only thing that I see (really a non-issue) will be that for any future issue a person will need to know the hot water comes from the additions tankless hot water heater for your sink and your shower. Again not really an issue - just a be aware that this is the case.

  • Thanks when I started I thought I was going to have to connect both hot and cold from the addition, and then I had an ahh haa moment and wondered if I could use the old one. Thanks for the info, connecting everything up tomorrow.
    – Kevin
    Mar 31, 2018 at 0:12

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