This question comes up alot but after searching the newsgroups I can't find a definitive answer to the following question:
I need to replace my old water heater with a unit made by Rheem. This Rheem tank has female tappings but no nipple connectors.
I am worried about galvanic corrosion at the water connections. The house has copper plumbing.
Is it best to connect the copper lines to the heater using brass nipples and brass adapters? Would it be better to use galvanized nipples and dielectric unions? I've even read that a male copper adapter straight into the tank is best. Which would you suggest?
What you read about a male copper adaptor into the tank being best is absolutely right.
Don't even think about using dielectric couplings (or unions) standing on iron nipples. They don't do a damn thing, they actually can make the situation worse. The insulating gap in those devices is electrically shorted out because the tank is electrically grounded (per code) and the copper piping is also grounded (again per code). They have their uses in other applications, but not in home hot water heaters.
I made the mistake of "upgrading" to a pair of dielectric unions with 2" iron nipples under them on the last heater I changed out in my house, without thinking about what was actually happening. One of the nipples corroded right through from the inside and started leaking within a year, and the other one wasn't far behind it!
I measured the galvanic current flow with that setup and proved that those galvanic unions were the wrong thing to use in that application. The galvanic current density is maximum right where the iron nipple joins the iron half of the dielectric union, and it burns through them pretty quickly.
When the dissimilar metals join right at the tank fittings, by using copper all the way to the tank, the sacrificial anode rod in the tank is "in view" to help take the corrosion hit, plus the steel tank fitting is a lot heavier than the tank shell and can withstand the corrosion currents a lot longer before it's shot..
The smartest thing you can do to prevent tank corrosion is to check the condition of the sacrificial anode rod a year or so after you install the water heater and judge from its condition how often you should replace it. (Sadly, that's a practice honored more in the breach than the observation.)
Happy New Year,
Jeff
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Jeff Wisnia (W1BSV + Brass Rat '57 EE)
"If you can smile when things are going wrong, you've thought of someone to blame it on."
Awwww, i'm not in the hot water tank thing at all. Now.
I changed my hot water tank out when i bought my house in 1979 and bought a Rheem tank and used this set up for running the water to it. Brass nipple out of tank on both, Then went to brass flex hoses on both to a brass ball valve on both, Then both valves screwed into a copper sweated on copper fitting to copper pipes on both. All the connections was brass when leaving the tank till it got to the copper water lines. Now I'm on my second water tank in 20+ years and the fitting are as good as new. I know it was a accident it was done this way but what is going on to make this set up work good ? Now I did have to change the rubber seats on the flex hoses after 20 years of operation but nothing else.
No accident TURTLE, brass is quite close to copper in the electrochemical series, so your using those brass fitings was just a smidgen away from as good the all copper pipe and fittings I claimed was "best".
Here's one of many primers on the subject. You'll note the author lumped copper and brass in the same box. He's describing corrosion on the outsides of pipes, but the principles are the same.
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All other things being equal (The same model tank and the same piping materials) there are other factors which can affect the longevity of the hot water heater and the plumbing fittings. Chief among them is the water quality with regard to disolved chemicals which affect its electrical conductivity, and that's something most of us can't easily modify.
You may be blessed with "good water" in that respect, for which I envy you. I can only get about six years out of a hot water heater where I live, even the "Nine Year Warranty" ones, before the tank shell rusts through.
As I mentioned in my OP, the galvanized iron nipples I used with the dielectric unions took a real corrosion hit in less than a year. If you want to see what the inside of the one which corroded through first looked like (after I scraped away the chunks of rust which had almost blocked off the nipple), see:
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It started leaking where indicated, at a thread root where the metal was thinnest. That was the end which was screwed into the steel half of the dielectric union, and that's located about where theory would expect the corrosion to be quite strong, close to the brass half of the union. And, while the brass and steel halves of the union weren't in direct electrical contact, they were connected through the heater's ground lead and the grounding of all the pipes in the house, which provided a return path for the galvanic current.
That's about the limit of my understanding of the subject, but I suspect other factors such as the temperature the hot water heater is set at probably have an effect on the rate at which electrolysis takes its toll.
Thank you here for i checked out what you had here and it was good to bring me up to date on them hot water tanks on corrsion and metal type fittings. I got about 20+ years out of my old hot water tank but the thermostat went out and the cost of a thermostat is just too high to replace. The metal electrode rod in them seem to be needed i guess but my old one did not have one for i took it out to get more water space for the water. Now on the new one i took it out too but i may go back and put it back for it can help on corrosion problem. i guess. We have good soft water to start with but you need all the protection you can get with corrosion these days. If it was not for the additive that has to be put in the water we would not need filters.
I just picked up some 3/4" x 18" Water Heater Connectors made by Watts Regulator (LS-202) that look pretty good. They have brass 3/4" FPT connectors on each end. These are then inserted in a polymer hose and the hose assembly is covered with a stainless jacket and crimped at each end over the inserted threaded brass connectors. The crimp is isolated from the brass connectors at each end by insulating washers on the outside and the hose material on the inside. The only electrical connection that can exist is that through the safety grounds to the water heater and the supply and output side plumbing.
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