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Old 31-01-2014, 21:11   #1
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Join Date: Nov 2013
Location: Los Angeles
Boat: 1979 Union Polaris 36'
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Fresh H2O Plumbing Manifold: Build one or valves at service locations?

Here's a weekend project I have going:

Replumbing the boat using soft copper for both hot and cold.
It's 1/2" OD refrigeration/HVAC stuff that is also for water systems.
I'm using the brass fittings for connections and flaring the ends, etc etc.
Home construction faucets with flexi-hose just like under the sink at home.


I have some long runs to the tankless LPG waterheater in the way back back of the boat. I'm assuming if I just T-off from the galley sink line on the way by there will inevitably be a pressure problem when we reach the waterheater at the end of the line if both are being used at once (such as using a mix of hot and cold flows at the galley sink).

To solve this problem I will run individual trunks to the Waterheater, Galley, and Head, and install valves on each line to regulate flow and try to equalize if possible. (Instead of just installing a T in all the most convenient places.)

This all becomes a question because tankless waterheaters need some pressure and flow to activate on, and my pump and water heater are far from each other. Plus, I want it to be just like home...

1) Will this plan work?

2) Should I build a manifold at the pressure pump (see pic) or install the valves before the sink fixtures more towards the end of the lines? (Or does it even make a difference??)

Thanks for anyone who has tackled this one before +-)
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Old 31-01-2014, 22:41   #2
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Boat: Islander 34
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Re: Fresh H2O Plumbing Manifold: Build one or valves at service locations?

The pressure pump only has a flow rate of about 3-4 gpm total. This is about what a 1/2" pipe can carry without getting too high a pressure drop. For the under 50' boat, you will be fine without the manifold.

The manifold design came about because pex uses insert fittings which basically adds a restriction orifice at each fitting.. Joy.. For PEX and a large house system, a manifold solved that nasty flow issues that pex has. For copper which is full bore across pipe/tube and fittings the old point to point tree system works fine.

So short answer, is either way will work fine for your boat. Not using a manifold will save some copper and fittings. I don't think you would see a difference one way or another as to flow rate, pressure or noise.

Unlike a house a boat does not have a dishwasher or washing machine. Well generally not until the larger boat sizes. So you don't have a really high flow rate.
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