Tankless On Galvanized Piping?

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Old 12-30-2017, 06:28 PM   #1
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Tankless On Galvanized Piping?

What is everyone's opinion on the viability of installing a tankless water heater in a home that has mostly old galvanized water supplies? I had someone ask me about this recently and I said I wouldn't recommend it. It seems like all that unavoidable rust will destroy the heat exchanger even if it's flushed a few times per year.

Has anyone had success or nightmare with this scenario?
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Old 01-01-2018, 10:43 AM   #2
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Re: Tankless On Galvanized Piping?

How about a filter on the cold water in side, one that could be inspected and cleaned/changed periodically?


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Old 02-10-2018, 08:59 PM   #3
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Re: Tankless On Galvanized Piping?

I believe the reason you don't want to connect a tankless water heater to galvanized water piping is because electrolysis is always the strongest near water heaters and the copper heat exchanger will get destroyed.

I've had a few customers who had tankless water heater heat exchangers leak 3 years in a row on brand new heaters.

About 30 years ago, a factory paid me $30,000 to run a 200 foot 3 inch copper water main from the water meter to their building. A week after the job was finished the company paid me to remove the copper and install a 3 inch iron water main because they had some sort of machine that attached to the water pipes and the instructions for the machine said there could be no copper water piping to the building nor in the building and the reasoning was due to electrolysis.
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Old 02-10-2018, 09:09 PM   #4
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Re: Tankless On Galvanized Piping?

Plenty of boilers use steel pipes. 40 years says it isn't a disaster. They use steel heat exchangers, so electrolytic corrosion isn't a problem.

Last edited by hdavis; 02-10-2018 at 09:11 PM.
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Old 02-16-2018, 04:25 PM   #5
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Re: Tankless On Galvanized Piping?

Rust isn't going to damage a heat exchanger. Should be benign. Amount of iron in the water could not be high enough to cause a problem or they would not be drinking it. As for electrolysis, there certainly be galvanic issues but I am sure the tank manufacturer would call that out and even then would probably only be a grounding issue.

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