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Old 09-27-2007, 09:39 AM   #1
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PEX to threaded connections

With poly tubing there are rubber compression fittings that allow for tight Poly-to-threaded connections.

Are PEX-to-threaded connections done the same way? I'm thinking specifically of my connections into and out of my hot water heater.

Thanks.

Scott
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Old 09-27-2007, 09:59 AM   #2
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Hey Scott,

I'm using Sea-Tech fittings almost exclusively now. You will most likely need 1/2" thread to 1/2" pex fittings. You can get them either straight or 90* connections as needed. They do have a rubber saniprene gasket on the threaded side and should only be made hand tight! They will leak of overtorqued.

Don't forget to add a check valve on the hot water outlet side of the water
heater.

You should be able to get these at Lowes or HD. They are now sold as Watts fixtures.

Let me know if you have any other concerns.
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Old 09-27-2007, 06:39 PM   #3
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Quote:
Originally Posted by lewster

Don't forget to add a check valve on the hot water outlet side of the water
heater.
Can you tell us why?
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Old 09-27-2007, 06:43 PM   #4
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Me too. I can get my head around a check valve on the inlet, but the outlet has me 'al puzzlemento'.
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Old 09-27-2007, 11:30 PM   #5
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Not exactly sure why, but it may be an RVIA design and certification requirement. AFAIK, a check valve on the hot side (I have seen these on just about every water heater installed by the OEMs) will keep the cooler water that resides in the piping from back-filling the tank. Other than that, I just do what I'm told .

I will check into it when I get back to the office in FL at the end of Oct.
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Old 09-28-2007, 12:20 AM   #6
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Moonshot,

A year ago when replacing my water heater, Qwest/pex 90degree to 1/2 or 5/8 brass was available at lowes. They worked quit well except the wall thickness of the pex fitting end was significantly greater. Caused a clearance problem I was able to overcome. Easy to tighten to the pex tubing.

Shark fittings are also suppose to be a first class system. They are also fairly large, brass & plastic, and a little more expensive. I have been told they are very easy to work with connecting or disconnecting. Shark was available at the plumbing supply.

The bypass valves available today are quite different than the old ones. They are available at camping world and are a true bypass valve.
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Old 09-28-2007, 09:13 AM   #7
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Thanks everybody.

As far as the check valve goes, I did not have one in the initial (original?) setup so I need to research that some more.

I don't plan to disturb the poly tubing that comprises by bypass system (for winterizing) just hook into the In of that system and the Out of that system. Thanks for the heads up on the Shark fittings. I know where to get them. They are expensive and I only plan to use them if nothing else will adequately work. Adequate being the keyword here.

I'll probably save this little bit of plumbing for the last and cut my teeth on the faucet and toilet hookups.

Scott
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Old 09-28-2007, 10:23 AM   #8
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Quote:
Originally Posted by lewster
Not exactly sure why, but it may be an RVIA design and certification requirement. AFAIK, a check valve on the hot side (I have seen these on just about every water heater installed by the OEMs) will keep the cooler water that resides in the piping from back-filling the tank.
Now it makes sense.

A check valve on the inlet side will keep hot water from back-filling into the supply cold water piping. A check valve on the outlet side will keep cold water from back-filling the water heater.

However, a check valve on the inlet side does not provide a second line of defense against overpressure in the water heater (the first being the T&P valve on the water heater itself).

As the water in the heater tank expands, a check valve on the outlet will allow the excess pressure to escape out of the pressure relief valve in the inlet water piping before it pops the T&P valve.

On the other hand, if the check valve is on the inlet side, the pressure will only have one way out, the T&P valve. The T&P valve is set at a much higher pressure than the regular relief on the inlet piping and may overpressure the piping before it pops.

This assumes you don't have an accumulator to absorb the excess pressure.
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