Hot water line size

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by keydash, Jul 15, 2010.

  1. keydash

    keydash New Member

    Uncertain about what size of hot water line to use.

    Small structure: 1 shower, lav, toilet, washer, kit sink.

    The cold water line is 3/4 pex reducing to 1/2 at the bibs, then to 3/8 at fixtures other than the washer. I will be using an on demand water heater connected to the pex through a length of iron pipe.

    Question: Should I follow the same sizing for the hot water line as laid out for the cold water line or just run 1/2 pex for the hot throughout? The water heater has a 3/4 inlet and outlet.
  2. nhmaster3015

    nhmaster3015 Master Plumber

    The granite state
    follow the manufacturers directions. On demand heaters are sensitive to flow
  3. jimbo

    jimbo Plumber

    San Diego
    Conventional wisdom says 3/4 copper ( 1" PEX) for the mains, reducing to 1/2" copper ( 3/4" PEX) for individual fixtures. These days, for low flow fixtures like lav faucets and showers, the smaller pipes have advantages. But for hi-demand fixtures like a tub or washing machine, you would quickly regret smaller pipes.
  4. Gary Slusser

    Gary Slusser That's all folks!

    I'd get rid of that piece of iron/steel pipe and since all tank less water heaters are flow controlled (already), I'd not run less than 3/4" to it. Steel/iron pipe rusts adding iron to the water and hard water voids the warranty on the tank less heaters.
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