Flexible Copper Pipe for Water Heater Installation & Cut-Off

natewallMarch 31, 2009

I have to replace my water heater. The old heater is connected with 3/4 inch rigid copper pipe and solder connections. I am thinking about using 3/4 inch flexible copper supply and feed lines, available at Home Depot, for ease of installation. I would use a 3/4 inch compression fittings on the copper pipes to the house to make the connections to the flexible copper pipe.

How well does the flexible copper pipe hold up? Does it leak over time (pin hole or catastrophic break)? Or should I just sweat solder rigid pipe to make the connections? Is it OK to use compression fittings on the copper piping to the house, or should I sweat solder male threaded adaptors on?

Also, I need to replace the cut-off valve (old one leaks). A gate valve is on the supply line. Can I replace it with the common washer variety of valve (compression valve), or should I use another gate valve or a ball valve?

Thank you.


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Absolutely use a full flow ball valve for your shutoff. It will not let you down like the gate valves will. I always use threaded valves and male adapters, along with a wet rag on the valve body, to keep from overheating the valve.

If you know how to solder, use rigid pipe. It looks more professional than the flex connectors. I'd rather have a soldered fitting than a compression fitting any day.

    Bookmark   March 31, 2009 at 9:08AM
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Agree on the 1/4 turn full flow ball valve with out question.

Short of soldering, here's a far better alternative than flex copper... SS flex

Doesn't work harden like copper and flows more volume. New John Guest model eliminates soldering.

    Bookmark   March 31, 2009 at 9:49AM
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You mean the corrugated copper flex, or just regular bendable? I wish I'd seen the corrugated copper, I ended up using the new braided ss flex hoses. I am assuming they are ok and not going to fail but will probably do a couple of small adjustments as I cut the copper a bit long so there's a bit of pressure on the pipe as the flex lines push themselves up to straighten if you know what I mean.

Absolutely go with the ball valves, worth every penny. You won't want to go back.

Make sure your water pressure is not too high, you don't want to kill your new tank. Also, do you have an expansion tank? If you have a pressure regulating valve (yes, the newer ones do allow for SOME thermal expansion) or a water meter or anything that incorporates a backflow preventer, you need an expansion tank.

    Bookmark   March 31, 2009 at 2:45PM
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Code requires the water heater main shutoff valve to be a "Full Bore Valve". Gate valves and Ball Valves are full bore valves.

The washer type valve described in the original post is a "Globe Valve". Globe valves are throttling valves and are prohibited by code for this application.

    Bookmark   March 31, 2009 at 5:17PM
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Thank you all for your input.

I decided to sweat solder the water connections and a ball valve in and use electrolytic coupling connectors at the water heater inlet and outlet steel pipe nipples, which will enable be to break the connections with a wrench for servicing the heater, if needed. This just seems more durable than copper flex lines and compression fittings for the flex line couplers-to-copper pipes.

What is odd is that the main water cut-off valve to the house is the old style (3/4 inch copper pipe) rising stem with seat and washer (is this a compression valve?), just like an outside faucet valve. This valve leaks a little, as well. The house was built in 1963, so I guess that is what was used then. It shure makes a racket when the water rushes through it when its turned back on, until the pressure builds up, but is quiet after that.


    Bookmark   April 1, 2009 at 9:32AM
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GREAT NEWS- You water heater installation now meets full code compliance.

In addition to a Full Bore Valve" (gate valve or ball valve) on the cold water supply line, you are also required to have a dielectric coupling between the copper and the steel tank vessel and a union within 12" of the water heater vessel.

If you used dielectric unions you satisfied both requirements with one fitting.

In regards to your main water shutoff valve. Code now requires the the main water shutoff valve must also be a full bore valve, however it is assumed that the globe valve you currently have met code approval at the time of installation and you may continue to use it until it fails. When it becomes necessary to replace that valve you would be required to upgrade to a ball valve or gate valve.

    Bookmark   April 1, 2009 at 10:54AM
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One final question: I have a decent sized copper ground wire running from the black iron gas pipe (going to the water heater) and to the cold water pipe before it attaches to the heater. I understand that this was done to make sure the water pipe is grounded in the event any of the house wiring contacts the pipe, energizing it. Grounded, it will trip the breaker. Do I need to now run a jumper from the cold water pipe to the hot water pipe exiting the water heater, since I have electrically isolated the heater with the anti-corrosion couplings, or is the hot water pipe electrically connected to the cold water side through the valves in the house, making a jumper redundant?



    Bookmark   April 1, 2009 at 11:25AM
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You do not not need to install a jumper because dielectic nipples and dieletric unions have a full metal to metal contact and do not electrically isolate the water heater from the piping system.

    Bookmark   April 1, 2009 at 11:57AM
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Hey Lazypup...

You sure about that?... The dielectric unions I've seen do exactly that. That's what makes them dielectric unions.

    Bookmark   April 1, 2009 at 8:43PM
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The NEC requires that any metal piping that's likely to become energized to be bonded to ground. You cannot assume that the hot water lines are bonded through the faucets - many are connected via plastic flex lines or plastic valve bodies.

You should bond between the hot and cold water lines at the heater. Typically that's done with a #6 copper wire and ground clamps.

The dielectric unions, if they are doing their job, are isolating the water tank from the plumbing and therefore can't provide a reliable electrical path.

    Bookmark   April 1, 2009 at 9:58PM
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Dielectric nipples or dielectric unions DO NOT isolate the tank from the piping system...don't believe it, get out your ohm meter and check for yourself.

    Bookmark   April 1, 2009 at 10:22PM
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In order for that test to be valid, you would need to remove any other possible paths including the gas line and the water in the pipes.

A more simple test is just to test the dielectric union itself.

But you can look at a union and see: there is a nylon collar and a washer that prevents electrical connection between the two metal pieces. The brass piece in this union is completely isolated. There is no metal to metal contact. As I said before, that's what makes it dielectric union.

    Bookmark   April 2, 2009 at 9:14AM
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Doing a search on this subject, what you will find are two different approaches:

1. That the NEC doesn't specifically call for it, therefore it's not required.

2. That the nature of plumbing has changed (meaning plastic supply lines) and you can no longer trust that the hot water lines are bonded through the faucets. Therefore it should be done even though it's not explicitly stated in the NEC.

Here is a link to the best explanation from what I believe is a reliable source.

Here is a link that might be useful: Hot water pipe bonding

    Bookmark   April 2, 2009 at 9:26AM
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Thanks again. My thoughts are that the electrolytic couplers do not conduct between the heater and pipe. I will check all of this out with my VOM. I'll also check the continuity between the hot and cold water lines. I am positive they are electrically connected because I just installed a new Price Fister tub 3-handle valve set and the valve body is brass, thus bridging the hot and cold water lines electrically.


    Bookmark   April 2, 2009 at 12:50PM
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I wouldn't worry about bonding the hot water pipe. I would insulate any exposed portions of the pipe and this would save you money and greatly reduce any chance the pipe would become energized. If you believe the pipes are still at risk and your strictly trying to follow the code, it gets more complicated. In my area, most houses less than 25 yrs old have polyethylene mains and switch at an inside meter, which don't qualify them as grounding electrodes. Pipe is not a suitable grounding conductor. So you cant use the cold water pipe as a grounding conductor to bond something else to the grounding electrode system. You would have to run a wire from the hot water pipe to the grounding electrode system. I don't see a problem if you are compelled to bond the hot and cold to eachother. They probably already are bonded through a shower valve in the house. In the end, I would make the decision based on the estimated risk the pipe becoming energized.

    Bookmark   April 2, 2009 at 12:56PM
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"In the end, I would make the decision based on the estimated risk the pipe becoming energized."


There is legitimate discussion about the need to bond the hot water to the cold at the water heater since until recently it was connected by other means and it isn't specifically called for in the NEC. Your statement that "They probably already are bonded through a shower valve in the house" leaves open the possibility that they aren't - which is the whole point here.

Bonding is not the same thing as using the piping for a grounding electrode. The NEC is very clear that all piping must be bonded to the electrical system.

It's not an option to decide if you want to bond the piping to the electrical system. Most certainly you don't get make a decision that "you don't think it will become energized, therefore you aren't going to bond it" as suggested by your last sentence.

Think of the implications if an un-bonded water pipe comes in contact with an electrical wire and then you go to take a shower, or do dishes, or any number of other things.

If it's bonded to the electrical system, it causes a breaker to trip. If not, everything it touches is energized.

    Bookmark   April 2, 2009 at 2:21PM
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The intrepretation of NEC 250.104 is dependent on your AHJ, so all piping is not required to be bonded. Some may require every isolated piece to be bonded, others may only require it to be bonded only at the entrance.

One of the biggest arguments against bonding all the isolated plumbing systems together (daisy chain) is they are not reliable means to ground. One plumber with a whole house filter can ruin all your work (and comply with all the plumbing codes in the process). If it is so important to ground all the plumbing then each piece should be bonded with a GEC and be required by plumbing codes during repairs.

A properly installed and supported electrical and plumbing systems have little chance on coming in contact with each other. Appliances attached to the system are the most likely cause of stray voltages and should be well grounded.

I've seen way many more cases of a voltage introduced from a "ground" on an isolated system, than ground protected faults.

    Bookmark   April 2, 2009 at 5:40PM
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