Brass Compression fitting direct from Copper tubing to Water Heater?

Just replaced my water heater, and my father in law came by to view my handiwork. He said he "thinks" that having a just a brass compression fitting between the copper pipe and steel nipples on the water heater will cause a "chemical reaction", and will "eat the pipe" over time. He said having a dielectric union inline instead would prevent this from happening.

I know next to nothing about these things, I was just happy it didn't leak and spray all over the place. My father-in-law is fairly knowledgeable, but he himself wasn't certain on this, just trying to give me a warning of possible things to come. I'd like to learn more, and would appreciate anyone weighing in with their knowledge on the subject. Thank you.

For a few bucks, the big box stores sells a dielectric union which I always install on top of the W/H.

Your father-in-law states the conventional wisdom that has been spread as fact for 20 years. It is not his fault. I think your brass coupling will do a better job than any di-electric union. I quit using them after the 15th time I replaced a water heater due to the di-electric unions disintegrating and causing the water heater to rust out. They are good for my repeat business but I prefer my customers have quality installations. I now only use brass unions at the water heater connection. No more corrosion problems.

Your brass compression fitting will be fine.

What he is referring to is galvanic corrosion, not some old myth it's very real. It's been giving plumbers hell for many years!

Matt30 said:

What he is referring to is galvanic corrosion, not some old myth it's very real. It's been giving plumbers hell for many years!

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I know he is. My extensive experience has shown me di-electric unions accelerate rather than prevent galvanic corrosion. Brass between copper and steel seems to stop the corrosion.

I know you know. I was trying to inform the original poster

For what it's worth, I side with SHR when it comes to di-electric unions. I have replaced more then I have installed

So, if I'm getting this right, the consensus seems to be that the compression fittings will be ok over the life of the water heater?

I appreciate the feedback. Thank you.

As long as you installed them so they do not leak; Yes.