I have a gas water heater inside my home at the moment. I am planning for the work to remove it, and install a new electrical tank-based water heater, at a different location. The new location is just on the opposite wall of the current location. It already has hot water and cold water pipes (that are currently simple taps). These pipes are the same diameters as the pipes currently going in and out of the current was water heater.

My plan is to close the pipes that are currently going in and out of the gas water heater (with a simple cap - I do not have the skills to properly crush them with a machine, and there is not enough space to do so). The length of these pipes will therefore become unused.

I am not sure how this will play out, but I imagine this could result in the length of these 2 pipes containing stagnant water : they will be filled in the first time I turn water on after installation of the new, electrical, water heater and then the water in there might not ever be used because it's a dead end.

Should I be concerned about that?

Here's a picture of the current gas water heater:

enter image description here

  • I've heard new code will do away with water hammers for exactly this reason, but we're all still alive aren't we?
    – Mazura
    Commented Feb 22, 2021 at 10:32
  • Hi mazura, can you develop a bit on water hammers? I googled it, but it pointed to a phenomenon of water slamming against something. It didn't seem related to my case?
    – DevShark
    Commented Feb 22, 2021 at 11:32
  • It's the same thing; a dead end piece of pipe (that can stagnate). The part about code was mentioned to me in passing and third hand information so IDK.
    – Mazura
    Commented Feb 22, 2021 at 12:12

2 Answers 2


no. my house has had a much longer capped hot-water stub line for 50 years and there have been no problems with it.

In the dark inside a pipe clean water does not become stagnant.

  • 1
    Hi Jasen, thanks for your answer. I am a bit confused by your first statement. When you say "this house", do you mean your house? Regarding your second point, I have read that legionnary disease was an issue in tanked water heater. From that, I assued that water could turn "bad" even if there was no light?
    – DevShark
    Commented Feb 22, 2021 at 11:34

There could be a safety problem with stagnant water, if the temperature is between 20 and 45 degree Celsius. In many jurisdictions, the rule is to avoid those dead lines connected to the drinking water net, especially if this apartment or building is rented out. Some comprehensive information concerning Legionella is given on this site, translated by google: https://semz5ily3x32q2in2jnj54ym2u-adwhj77lcyoafdy-www-bosy-online-de.translate.goog/Legionellen.htm. And here are infos about best practice for drinking water nets: https://semz5ily3x32q2in2jnj54ym2u-adwhj77lcyoafdy-www-bosy-online-de.translate.goog/Trinkwasser-Leitungssysteme.htm

  • Hey @xeeka, thanks for that. I was worried about that. Given that the pipe is vertical, do you have an opinion on whether water will stagnate, or will actually tend to circulate?
    – DevShark
    Commented Feb 22, 2021 at 14:11
  • 1
    Due to temperature difference there could be some micro- circulation inside each tube. But it is not a good idea to let the safety/health of the users depend on that effect, especially in case of older people or people with an immune system of lower performance.
    – xeeka
    Commented Feb 23, 2021 at 0:40

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