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Old 22-01-2016, 18:11   #1
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Pex to Hot Water Heater

Hi,

What is the proper way of connecting PEX piping to a marine hot water heater? Are their guidelines regarding the installation? Our current setup:

Hot Water Out->Bronze 1/2" nipple->Bronze T Fitting -> 2 x Plastic pipe to hose barb->vinyl tubing.

I was hoping I could do this:

Hot Water Out->PEX 1/2" Pipe to 3/8" tubing fitting->PEX tubing->manifold

However, I saw that home installations require you to run copper pipe the first three feet out of the hot water tank. Is this also true for marine installations?

What have you done?

- z
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Old 22-01-2016, 18:34   #2
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Re: Pex to Hot Water Heater

I terminated the pex about two feet away from the heater on both hot and cold sides with male npt fittings then used off the Home Depot shelf flexible supply line hose (faucet stuff) to make the jump.


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Old 22-01-2016, 18:37   #3
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Re: Pex to Hot Water Heater

There is a diagram in this manual
http://itrheat.com/wp-content/upload...hyr-Manual.pdf
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Old 22-01-2016, 19:44   #4
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Re: Pex to Hot Water Heater

Shark bite makes a pex to female fitting. Just thread it to the tank (use teflon tape and push the pex on. Easy.
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Old 22-01-2016, 19:54   #5
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Re: Pex to Hot Water Heater

I'm guessing the three foot distance helps to ensure that the pex won't be exposed to the full heat of water in the tank, as a safety measure. FWIW home hot water tanks are often set at 140F to 160F in order to make sure the water is still scalding hot when it gets to the furthest fixture, even though building codes usually limit it to 120-125F to prevent scald injuries. So there's a lot of variable in terms of just how hot parts of the system may be exposed to.
If you're sure your tank won't overheat the pex...you wouldn't need the three foot space. If you can be SURE.
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Old 22-01-2016, 20:05   #6
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Re: Pex to Hot Water Heater

Quote:
Originally Posted by hellosailor View Post
I'm guessing the three foot distance helps to ensure that the pex won't be exposed to the full heat of water in the tank, as a safety measure. FWIW home hot water tanks are often set at 140F to 160F in order to make sure the water is still scalding hot when it gets to the furthest fixture, even though building codes usually limit it to 120-125F to prevent scald injuries. So there's a lot of variable in terms of just how hot parts of the system may be exposed to.
If you're sure your tank won't overheat the pex...you wouldn't need the three foot space. If you can be SURE.
Pex is rated for 200 degrees F at 80 psig or 180 degrees F at 100 psig. Should be fine for a boat water heater. The higher the temperature the lower the working pressure. Never had problems with mine.
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Old 22-01-2016, 20:24   #7
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Re: Pex to Hot Water Heater

Quote:
Originally Posted by hellosailor View Post
I'm guessing the three foot distance helps to ensure that the pex won't be exposed to the full heat of water in the tank, as a safety measure. FWIW home hot water tanks are often set at 140F to 160F in order to make sure the water is still scalding hot when it gets to the furthest fixture, even though building codes usually limit it to 120-125F to prevent scald injuries. So there's a lot of variable in terms of just how hot parts of the system may be exposed to.
If you're sure your tank won't overheat the pex...you wouldn't need the three foot space. If you can be SURE.
That is correct most home water heaters are set @ 140 degrees. Boat water heaters when using the engine heat exchanger typically run much hotter, 160 -180 degrees. Although there are many out there that have made a direct pex to water heater connection & gotten away with it, doesn't make it right. I'd recommend seeing what the manufacturer of the "pex" product you're using recommends & go from there.

The good thing about a boat, blow a pex line you drain the fresh water tank, blow a pex line in a house, the canoe floats in the basement.
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Old 23-01-2016, 08:35   #8
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Re: Pex to Hot Water Heater

Our water heater has a heat exchanger which uses our 200F engine water.

We use Qest fittings and Pex pipe. No issues in 9 years...
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Old 23-01-2016, 11:20   #9
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Re: Pex to Hot Water Heater

Quote:
Originally Posted by zboss View Post
Hi,

What is the proper way of connecting PEX piping to a marine hot water heater? Are their guidelines regarding the installation? Our current setup:

Hot Water Out->Bronze 1/2" nipple->Bronze T Fitting -> 2 x Plastic pipe to hose barb->vinyl tubing.

I was hoping I could do this:

Hot Water Out->PEX 1/2" Pipe to 3/8" tubing fitting->PEX tubing->manifold

However, I saw that home installations require you to run copper pipe the first three feet out of the hot water tank. Is this also true for marine installations?

What have you done?

- z
I went out to the garage to check. I have PEX running right up to a sixty gallon hot water tank. It even has the tubular foam insulation around it.

It has not been a problem.

For what it is worth.
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Old 23-01-2016, 11:26   #10
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Re: Pex to Hot Water Heater

I converted my water system from CPVC and reinforced hose to PEX earlier this year. The water heater in and out had CPVC so I chose to keep about a foot of the CPVC where it terminated to the heater because the fittings and pipe were in very nice shape. I used shark bite PEX push on fittings that are designed to transition from PEX to CPVC. I got them at Home Depot and they worked awesome.
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Old 23-01-2016, 12:59   #11
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Re: Pex to Hot Water Heater

Here is a blog post of our conversion from copper plumbing to the Pex system. There is a good photo of the connection to our hot water heater. The Trawler Beach House: 30-Year-Old Boat Plumbing Replacement . Chuck
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Old 24-01-2016, 09:46   #12
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Re: Pex to Hot Water Heater

I can only recommend what the standard in the "plumbing" industry is. When I see CPVC & PEX manufacturers recommend that their products not be used for a direct connection to a water heater or boiler, there's a reason for it. Could be they've had some failures & the disclaimer is to protect themselves from any liability. Typically it's not the piping material itself that fails, it's the IPS mechanical connection especially with CPVC. Even some of the Plumbing codes address this issue.


My point is given the operating temperatures of a boat heat exchanger it would be best to check with the pipe /fitting manufacturer to ensure the product is acceptable for the specific application. That's all...
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Old 25-01-2016, 14:41   #13
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Re: Pex to Hot Water Heater

I'm going to be going through a thermostatic mixing valve (so the output temp should always be below the PEX temp) and then to a hot water heater whip connection to the PEX manifold.
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Old 25-01-2016, 14:58   #14
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Re: Pex to Hot Water Heater

In here (other side of the pond) we have a mixer vent after the boiler to lower the water temp going to pipes and to relase overpressure. Copper btw it and the boiler, I installed mine with 4" length of copper. After that with PEX..
Never seen (about 25yrs, as PEX became the standard those days) anything else..

BR Teddy
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Old 26-01-2016, 13:45   #15
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Re: Pex to Hot Water Heater

Quote:
Originally Posted by sailorchic34 View Post
Shark bite makes a pex to female fitting. Just thread it to the tank (use teflon tape and push the pex on. Easy.
Exactly what I did and works GREAT!!!
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