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Old 04-12-2018, 00:18   #1
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1/2" or 3/4" PEX?

I patched my water tanks and replaced a bunch of supply hoses last spring on the Columbia 10.7 I bought last December. I chose to base my system on 1/2" hoses.

I have a sink in the galley, a sink and a shower in the head. The boat originally had a hot water heater but it was removed.

My plan is to eventually replace the hot water heater, but for the moment I will live with cold water only.

The current hoses are Ok but air is getting into the system somewhere and I'm thinking I'd like to switch to PEX.

So, the question is: What is the preferred size for the system I'm envisioning, with hot and cold water, and three outlets?

1/2" or 3/4" tubing?

And, what size pump?
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Old 04-12-2018, 05:39   #2
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Re: 1/2" or 3/4" PEX?

It depends on whether you want volume or pressure. The 3/4" pipe will provide more volume at the same PSI but less pressure. "Good" pressure in houses is generally around 45-55 psi. 12v pumps for 50 psi are easy to find. You can get higher psi pumps, but on a cruising boat fresh water is often a resource you don't want to waste. I would go with 1/2" pipe and an adjustable psi pump up to 100 psi. Then you can control the pressure based on how much water saving you need. YMMV.
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Old 04-12-2018, 05:40   #3
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Re: 1/2" or 3/4" PEX?

1/2" PEX is the usual size to use. Fittings are everywhere...Homedepot not Westmarine!
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Old 04-12-2018, 05:58   #4
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Re: 1/2" or 3/4" PEX?

Why do you need to heat hot water?
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Old 04-12-2018, 06:41   #5
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Re: 1/2" or 3/4" PEX?

For heck sakes, even 3/8" would do. 1/2" is all you need for sure. 3/4" only if your goal is to drain tanks as fast as possible. Note that if you install HW heater, larger pipe means much longer wait for hot water at the tap or shower head (and more wasted water). Forget the 3/4" PEX, unless large yacht with long runs.
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Old 04-12-2018, 06:46   #6
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Re: 1/2" or 3/4" PEX?

Might add, if your tank connection is 3/4" might make sense to run 3/4" to the pressure pump suction. But that's about it.
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Old 04-12-2018, 06:47   #7
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Re: 1/2" or 3/4" PEX?

If you are going to be showering on board, Id recommend 3/4".
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Old 04-12-2018, 07:09   #8
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Re: 1/2" or 3/4" PEX?

3/8" or 1/2".
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Old 04-12-2018, 07:17   #9
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Re: 1/2" or 3/4" PEX?

Typically you want a 3/4" main with 1/2" branches to the fixtures. This will help keep the flow and pressure from dropping to much when/if multiple fixtures are used at the same time.

But on a boat with only 3 fixtures, a simple system with 1/2" throughout would be fine.
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Old 04-12-2018, 07:41   #10
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Angry Re: 1/2" or 3/4" PEX?

On my 2005 Hunter 38 with 2 showers, kitchen and bathroom sink the piping is factory installed 15mm PEX. Blue for cold & red for hot water. Pex can be bend, but it put a lot of strain on the fittings, better use a 90 fitting, less leak prone. Ask me how I know
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Old 04-12-2018, 08:51   #11
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Re: 1/2" or 3/4" PEX?

1/2" will be fine, make sure you use full flow fittings.
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Old 04-12-2018, 08:55   #12
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Re: 1/2" or 3/4" PEX?

1/2" would be much easier to work with, I would think that with the small number of "taps", 1/2" would more than suffice. Keep it simple.
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Old 04-12-2018, 08:58   #13
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Re: 1/2" or 3/4" PEX?

Thanks for the input. Looks like 1/2" is the winner. Whenever possible, I try to avoid 90 degree fittings. I prefer Ys or 45s.
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Old 04-12-2018, 09:07   #14
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Re: 1/2" or 3/4" PEX?

1/2", more velocity.
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Old 04-12-2018, 09:16   #15
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Re: 1/2" or 3/4" PEX?

Quote:
Originally Posted by Outlaw7 View Post
Why do you need to heat hot water?
20,000 comedians are out of work and you are trying to be funny...

Ha, ha
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