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Thread: Unused copper gas pipe hot to the touch

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    DIY Junior Member eeka's Avatar
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    Default Unused copper gas pipe hot to the touch

    Hi, I was hoping someone might know the answer to this.

    I live in a three-family (stacked/three-decker) home built in 1893. I own and occupy the third floor only.

    About two years ago, I had several thousand dollars worth of plumbing done on my unit by a very reputable company that does tons of work in my area. I was in the process of renovating my kitchen and discovered horrible scary plumbing (including drain pipes running uphill and car radiator hose used as supply lines!) tied into the original plumbing presumably when the place was renovated in the 1990s a couple of owners ago. I decided to call plumbers and have them rip out everything in my unit and redo it out to the original plumbing, which they said was still in great shape. They redid the gas line to my stove as well.

    Today, while laying new floor in my kitchen, I discovered that the old, unused gas pipe is really hot to the touch (it's usually behind a freestanding counter/cabinet unit so I don't notice it). The pipe is partially embedded in what looks like some sort of concrete leveling material where the wall meets the subfloor, so the pipe was left and a new one was just put in along the wall above that. I'm certain that this is old pipe and isn't hooked up to gas; the end where the stove used to be is open and clearly not leaking gas, and I can follow the new gas line from the stove into the wall where the plumbing enters the unit.

    Does anyone have any idea why the pipe would be hot? Is it something I should worry about, or is the other end of it probably just really close to something else hot in the walls, like a heating pipe? Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Copper is a pretty good conductor, so if it ran near something hot (water, hot water heat, heating duct), it could get warm. The only other thing I can think of that might make it hot is if it was acting like a heating element, and it was electrified. If that was the case, you'd have probably noticed when you touched it!
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member dlarrivee's Avatar
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    It could be as simple as a heating duct being right next to it.

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    Moderator & Master Plumber hj's Avatar
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    quote; The only other thing I can think of that might make it hot is if it was acting like a heating element, and it was electrified. If that was the case, you'd have probably noticed when you touched it!

    Only if he were "grounded" when he touched it. I have had many conditions where something was "electrified" but the occupants of the building did not know it because they could not touch the item and a source of grounding at the same time. Without being there, it is impossible for us to tell you WHY it is hot, but I would advise you to find out instead of guessing.
    Licensed residential and commercial plumber

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    DIY Junior Member eeka's Avatar
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    Default Not electrified

    Hadn't thought of the possibility of it being electrified, but that's certainly not out of the realm in this house. I just checked it with a voltmeter and it's not giving off anything.

    So if it's just conducting heat from being near a heating pipe or hot water pipe and isn't touching anything particularly flammable, is there any reason I need to do anything other than just leave it alone?

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    Moderator & Master Plumber hj's Avatar
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    quote; I need to do anything other than just leave it alone?

    YES! You should find out exactly WHY it is getting hot, before you shrug it off as being "normal". And how are you using a voltmeter to test it?
    Licensed residential and commercial plumber

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    DIY Senior Member jastori's Avatar
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    The only way that a copper pipe could get hot from electrical resistance heating is if a *lot* of current were flowing through it.

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    Nuclear Engineer nukeman's Avatar
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    What do you consider "a lot"? 100 mA? 1A? 10A? 1000A? You could certainly heat the thing up depending on how much power you are putting into it.

    Likewise, we need to know how "hot" this pipe is. Is it say ~100F, 150F, 200F, etc.? If it was say 100F, it could be from a duct or similar, but if it was say 150F, we know that it isn't a heating duct or HW line, but could be due to something that is higher temperature (boiler flue, steam/water boiler supply, etc.).

    Without another energy source (electric current, etc.), the temperature can only be lower than the source that is heating it. By knowing the temperature, we could better figure out what might be making it hot.

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    DIY Senior Member jastori's Avatar
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    Well, 12 GA copper wire can safely carry 20 A. A copper pipe has a lot more cross sectional area than 12 GA wire. So, I'm figuring it would need to be more than 20A to make the pipe hot to the touch. If there were more than 20A flowing through the pipe, there would likely be high electric bills & circuit breakers blowing..... not impossible, but very unlikely to have that much current flowing without any other symptoms

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    DIY Junior Member eeka's Avatar
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    Thanks, all!

    How did I check with voltmeter? I put one probe to a ground and other probe to the copper pipe. It stayed at zero. Same voltmeter registered 122V between hot and ground.

    I'm not sure how hot it is, and I don't think I have anything I could test the temperature of a pipe with. I'd say it's probably a bit cooler than a typical heating pipe or hot water pipe; I can touch it for a few seconds, but imagine I'd get lasting burns if I pressed against it for any length of time.

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    DIY Junior Member eeka's Avatar
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    Default Location of other stuff

    FWIW, the boiler flue is in a known location, nowhere near the mysterious hot pipe (all three boilers are in basement, flues go up into a brick chimney in the center of the house that used to be for fireplaces).

    All of the plumbing and the gas lines to the units are inside a wall right near mysterious hot pipe (dead space in between kitchen and bathroom).

    The radiator pipes are as you'd expect, running in a circle around the exterior wall (hot pipe is also along outside wall in kitchen) but unsure where exactly they come into the unit from the basement. Would guess it's all in that same wall since the house was built before indoor plumbing and would have been retrofitted.

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    DIY Member mliu's Avatar
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    Is it protruding through drywall (gypsum board) or plaster and lathe? If dryway, I'd cut an inspection hole in the wall near the pipe and then repair it myself; drywall is very easy to work with. If plaster and lathe, I'd hire a contractor who specializes in that work to cut and repair the hole. No matter what the wall is made of, you need to open it up and find out exactly what is heating that pipe. If you're not able to determine the cause from first-hand observation, then how can any of us guess what's causing it?

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    DIY Junior Member eeka's Avatar
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    It's coming up through the floor. It's embedded in some concreteish stuff, which looks like it was used to level the floor before new tile was put in. No way to get into it without really messing up the floor.

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