Rehabbing an old hot water tank

[Robb]

I've picked up an old 80-gallon stone-lined high-temperature solar hot water tank -- the kind from the 80s with the copper heat exchanger built-in. Don't ask me how I got it out of that guy's basement. "Sturdy" would be the delicate way to describe the tank's weight.

There's some corrosion on the connections... I'm thinking I need to replace the nipples and drain valve at a minimum. I know there's a de-scaling product out there that's nice and toxic; anyone know if that stuff will damage the copper coils, or if it's OK?

[jeff47]

1. No idea if this applies to this kind of piping...

...but on copper potable water pipes, you don't want to remove the "rust". It's a thin layer that's permanently stuck to the metal, and keeps the rest of the pipe from rusting. (As opposed to iron rust, which flakes away and exposes new metal).

So in copper potable water pipes, the inside of the pipe quickly rusts, but it stays there. Removing that rust makes the pipe thinner, and the newly-exposed metal rusts again, resulting in a thinner pipe.

However, this isn't a potable water situation, so I don't know if the same applies.

If it's just build up from minerals in the water, soaking in a relatively weak acid should dissolve those minerals quickly without harming the pipes. Think vinegar-level acidity, but you'll probably want to mix it up from a cheaper acid, such as muriatic. Too strong of an acid solution will indeed eat the pipes.

[NMDemDist2]

2. this is a potable water situation seems to me

a hot water tank definitely uses potable water

interesting about copper 'rust' i had never heard that, good to know, thanks!

[Robb]

3. I hadn't thought of it that way

...since I was concerned about stuff on the outside of the copper tubing coils. But you're right, the principle should be the same. Perhaps I shall just leave well enough alone and hope any buildup doesn't overly affect the heat transfer.

[lumberjack_jeff]

4. are there anodes in it?

If so, replace them.

[Robb]

5. Nope, stone-lined tanks apparently didn't need them.