Hot and Cold PEX Connections to the Water Heater from Below

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Tintin

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I have pex stubbed out of the wall down low and need to run the line up the behind the electric water heater to make the connections at the top--what's the best way to do this? Should I connect the pex to flexible copper pipe and secure those lines to the back wall as they go up? Can I stick with pex all the way up and make a connection at the water heater, or is it not code to use PEX for the connection? I usually see the flexible lines running down from above, so I'm not sure the best way to run the pipe up from below is? Thanks for the advice!
 
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Reach4

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You should not run PEX for, I think, the last 18 inches.
 

Tintin

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You should not run PEX for, I think, the last 18 inches.
Thank you, I appreciate it. So would you run the pex up the wall (clipped to it) to reach above and then connect an 18" flexible copper pipe over to HW connections on top?
HW Heater.jpg
 
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Reach4

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Thank you, I appreciate it. So would you run the pex up the wall (clipped to it) to reach above and then connect an 18" flexible copper pipe over to HW connections on top?
I have not done it, and I don't find a good example.

What size PEX do you plan to run, and what size threads will your water heater have? You might run 1 inch PEX, even if your WH has 3/4 threads. PEX is smaller for the same nominal size than the NPT that is used on a WH. Most WHs use 3/4 NPT, but some use inch.

You want to have a ball valve on the incoming cold. You may want a thermal expansion tank.

https://terrylove.com/forums/index.php?threads/tie-pex-into-water-pipes-at-water-heater-hows-this-look.45776/ is a thread that discusses some of these. Maybe after you do your, you can post a photo that others can use as an example.
 

Tintin

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I'm running 3/4 pex and the WH has 3/4 threads. Brasscraft makes a few connectors that go from pex to the water heater, so I think this should work:
3/4 in. FIP/MIP x 3/4 in. PEX Barb x 18 in. Copper Water Heater Connector (7/8 in. O.D.)

I have a shut off valve for the water close by under the sink, so I don't think I need the ball valve on the incoming cold. And my pressure is at 50psi with an open system, so I think I won't need the expansion tank either.
 

Reach4

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Another kind of connector could be a drop ear elbow.
10A580_AS01

That depends on your situation, but it does give you a nice support point if you have a wall at the right place.


I have a shut off valve for the water close by under the sink, so I don't think I need the ball valve on the incoming cold.
One for the WH is a good idea. I don't know if it is required by code.

Do you know about thermal expansion tanks? If not, I would do some reading.
 

Jadnashua

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Where I live, to pass an inspection every WH installation needs both an expansion tank and a vacuum relief valve. Your safe bet is to include an ET in your install, as the utility may add a check valve (if it doesn't already exist) on some future routine maintenance, and then, without one, you'll have problems.

While not as problematic as on a gas-fired WH verses an electric one, code doesn't want the plastic pipe (this includes CPVC as well) within, 18", as was already quoted. IF there's a problem, plastic pipe cannot handle the potentially above boiling water temperatures (the T&P valve wont' open until the pressure exceeds 150psi, or the temp exceeds 210-degrees F - neither of which is a good thing for plastic pipe).

With 3/4" pex feeding your WH, you'll not be able to achieve the maximum flow rate out of it. That may or may not be an issue in your use pattern. It all depends on the volume you need which is based on the quantity and type of fixtures it must simultaneously feed during their use.
 
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