pipeplumbingwater-heater
My water heater is hard-plumbed with galvanized pipe. It is at least 20 years old and is leaking:
I want to use modern flexible hose for the new water heater, but I don't know the best way to change the existing setup. I could simply take off the unions and try to thread adapters to the pipe stubs, but I'm concerned that the existing threads will have corroded to the point where it won't make a good connection.
How should I proceed?
With brass connected to galvanised pipe you can get some galvanic corrosion. There is something called a dielectic union which I've never needed to use. That may help. You'll need to clean up the rust. That may require cutting out the rusted part or at least scraping it off.
Here's a picture that describes the dielectric union joint.
You should be able to replace the flex pipe with a 3/4" PVC pipe using a threaded 3/4" connector. For a easier installation use a 3/4" union fitting at the meter. You could also install a shutoff valve at the same time.
Best Answer
Keep the unions.
If (as seems unlikely, given the over-all condition, despite one differing opinion) you can't get the pipe out of the old union-half, go purchase two new half-unions (or complete unions if you can't source the correct half-unions alone - take the half-union you remove with you to the store to match it) and connect your flex-hose to the half-union. Otherwise just unscrew the pipe from the half-union and screw in the new flex hose, or any adapters you need to connect to the flex-hose.