When I moved into this house the hot water heater (3 years old now, gas unit) was hooked up to the existing system with copper fittings. The whole house has copper supply lines.
1. Should I put dielectric fittings between the hot water heater and the copper lines? I know the dissimilar metals will cause the metals to corode faster.

2. Can I use brass fittings between the hot water tank and the copper pipes instead of the dielectric unions?

Hey Tommy,

You don't have to change a thing. We pipe all our new construction water heaters copper to copper and haven't got the first complaint of electrolysis yet.
Unless you have a faulty electric system it won't happen. Regards, Tom

I think where you really get in trouble is mixing copper and galvanized. I replaced a galvanized nipple between a copper line and a brass fitting last week. It was badly corroded. Of course it may have been 40 years old too. Frankly I don't understand why there is so much galvanized still being used. The stores are full of it.

Speedball,
What do you mean copper to copper? I thought the water heaters were some kind of steel which makes it a copper to steel connection??

We come out of the heater with 3/4" copper male adapters and go from there with copper. Hence, copper to copper. If this set up disturbs you come out of the heater with 3/4" brass short nipples and convert to copper with 3/4" female adapters. Dielectric unions should not be necessary. Good luck, Tom

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Originally Posted by speedball1

We come out of the heater with 3/4" copper male adapters and go from there with copper. Hence, copper to copper. If this set up disturbs you come out of the heater with 3/4" brass short nipples and convert to copper with 3/4" female adapters. Dielectric unions should not be necessary. Good luck, Tom

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"Speedball Tom",

Greetings from "Tankless Tom". This is my first post on this site. I started my search on Google with the term: "dielectric union" to try to answer a question I have about the effect their absence may or may not have on the rest of the plumbing in the house, specifically various valves and fixtures.

The house was owned and lived in by our family, but is now being rented out. It is about 40 yrs old. I installed a solar hot water system in about 1982 which is still working but about to spring leaks. We plan to take it all out and install a tankless water in its place.
(I work for the world's largest maker of tankless heaters, so it makes good sense, not that it wouldn't anyway! :))

Okay, the real issue: We recently tried to install a new dishwasher, and found one of the hot water angle stops all rotted when we tried to connect to it. It is only about 15 yrs old. Upon calling in a plumber, he tells us that ALL of them are bad and that the cause was the lack of dielectrics on the gas fired 40 gallon tank that has been in since maybe 1982 also. He installed a set of unions and replaced all valves including even the front main water shut off valve which was apparently bad also!

Does this sound right to you? I am not really doubting that the valves went bad, but I have never heard of the copper to galvanized connection "poisoning" the entire system like he said this did.

Lastly, I am a bit confused with your post above. You say that you come out of the heaters with 3/4 male copper adapters. How can you do that when the top of the heater has 3/4 galvanized pipe coming out?

Also, in another post you say that dielectrics are "good insurance" and even quote "Hammerzone" in your post. Yet you later state that you don't use them in new construction. I'm not trying to cause any trouble, just a bit confused.

Thanks for your patience with this long post,
Tom :confused:

The answer is yes you can use a brass water heater union or a dielectric. Don't ever put a 3/4 copper male adapter into a water heater. I also would not trust speedball for anything after hearing his answer. (far from an expert)

1. Should I put dielectric fittings between the hot water heater and the copper lines? I know the dissimilar metals will cause the metals to corode faster.
1. No
2. Can I use brass fittings between the hot water tank and the copper pipes instead of the dielectric unions?
2. Yes

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Originally Posted by a real plumber

the answer is yes you can use a brass water heater union or a dielectric. Don't ever put a 3/4 copper male adapter into a water heater. I also would not trust speedball for anything after hearing his answer. (far from an expert)

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Gee Thanks for that glowing opinion. In all the years. And the hundreds of water heaters my company installed in the 80's in the Condos and single family residences we have had zero complaints, ( let me repeat) ZERO COMPLAINTS! on any of the water heaters we installed. I retired before heat trap nipples came out but we soldered up 3/4" raisers on to 3/4" male adapters outside the heater so we didn't melt the flare on the cold water dip tube and cranked them in.them in. I believe I also said

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If this set up disturbs you come out of the heater with 3/4" brass short nipples and convert to copper with 3/4" female adapters. Dielectric unions should not be necessary if brass nipples are used.

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I was also around when "S" traps were used. Want to bust my chops about that? Tom