# How to trace gas pipe?



## karma_carpentry (Aug 7, 2005)

In a bathroom remod on an old Boston Victorian built in 1877 that's been remodeled countless times, I've come across a gas pipe in the floor, that's flush with the top of the original subflooring. It's iron with threaded fittings. There was an oak floor above it, actually touching it, and then lino then tile above that.

I've taken off the subflooring to sister on levelers to the joists. I'd love to cut out this gas pipe that is probably dead but I can't be sure. I don't want to leave a gas pipe flush with the subfloor. (By the way, I'm walking on the bare joists above a 3' deep dead space created by a previous remod that lowered the grand ceilings below. Grand scale of old work.)

Does anyone have tricks on tracing out a gas pipe? I tried knocking it with a metal rod and having a helper listen around. Didn't work. It's really buried in ancient walls and under the neighboring room's floor too.

I will ask the plumber when he gets in there to face the other mess -- literally dozens of drain and supply and vent pipes winding around each other in the 7 1/2" deep wall, from different eras. But if anyone has tips it would be great to get this pipe out of the way before working with the floor.


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## mdshunk (Mar 13, 2005)

Ohm it out. Connect one lead with a long wire to the known, charged gas line. Take the other meter lead and touch the suspect disconnected gas line. See if you have continuity. Not a 100% foolproof test, but a pretty good one. 

These old gas lighting lines were always laid in shallow notches in the floor joists for some reason. 99 times out of 100 they are dead. Sometimes I hijack unused gas light pipes and use them as a conduit from one area of the house to another if it works out.


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## karma_carpentry (Aug 7, 2005)

See, that's the genius tip I was looking for when I posted it here! I did think briefly about doing something with electricity, like giving it a 24V potential using a drill battery, and running some cable around to the basement to test for the 24V... but then I thought "well, everything is touching somewhere in this old house" and canceled this idea. But now you got me thinking again --> if it shows continuity with a dead gas line, and no continuity with the new live one, then I will feel pretty confident - enough to unscrew a segment (with some Hercules #5 nearby to be sure) and sniff for gas.

thanks Marc.


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## Teetorbilt (Feb 12, 2004)

I think that it's time to call in a gas pro. A water leak is one thing, a few sparks before the breaker blows may be a bit worse, the chance of blowing your house a few streets away in all directions????????????


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## mdshunk (Mar 13, 2005)

Teetorbilt said:


> I think that it's time to call in a gas pro. A water leak is one thing, a few sparks before the breaker blows may be a bit worse, the chance of blowing your house a few streets away in all directions????????????


Before what breaker blows? We're talking about using a meter here. Besides, I'm sure you're well aware of the amount of gas that would have to build up to cause such an explosion. It's important to understand the risks associated with any remodeling task. That is for sure. Blowing the house to kingdom come while tracing out a gas line is among the most remote of such risks. 

Personally, I wouldn't hesitate for a second to spin a pipe cutter around one of these gas lines if the meter tracing seemed to indicate that it didn't have continutity to a known charged line. Worst case, you'd have a little "torch" of sorts coming out of the gas line if you did happen to cut off and somehow spark off a charged line. Having someone standing by at the meter stop would be the thing to do in any event. 

Perhaps it is my HVAC background that causes me to feel that gas is not the big bad wolf that people make it out to be.


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## Tom R (Jun 1, 2004)

karma_carpentry said:


> Does anyone have tricks on tracing out a gas pipe? I tried knocking it with a metal rod and having a helper listen around. Didn't work. It's really buried in ancient walls and under the neighboring room's floor too.


Don't know any 'tricks', - - but can you see the bottom of that particular pipe nipple where it makes it's first turn??

If so, I would turn off the main gas, and trade out that nipple for a shorter one, and then re-cap with a galvo.

Then back on with the gas and re-light the pilots.

Use soapy water or a 'leak-detector' solution to check your connections before closing-in again.


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## Teetorbilt (Feb 12, 2004)

md, the way that I read it was "probably dead but I can't be sure" and "everything is touching somewhere". The "probably" part is what attracted my attention. I love explosions but not the unexpected kind. I'd still call in the guys with the proper knowhow and tools.


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## mdshunk (Mar 13, 2005)

Karma... would it be easier for you to trace the known charged line instead of the suspect one? If the basement is open, it should be pretty easy to trace it from the meter to the furnace, water heater, range and whatever. Then you could see if there are any branches off that you don't know where they go. If every branch on the known charged line is accounted for, then your ones under the floor are dead. Maybe you already thought of that, and can't do it for some reason. Just thought I'd throw that out in case it never dawned on you.


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## PipeGuy (Oct 8, 2004)

call some rental centers and ask about a 'pipe horn' for locating concealed or buried pipes.


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## nadonailer (Nov 15, 2005)

Call American Leak Detection (or similar company) and have them do a pipe locate for you. That way you know for sure exactly where it is. They can locate and mark all the pipes in the house while they are there. I used to own one of these franchises and they are really good. :thumbup:


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## Teetorbilt (Feb 12, 2004)

I've had experience with this co. too, all ++++ $185 to locate and repair underground water leak. :thumbsup:


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## Tom R (Jun 1, 2004)

Oh, - - not too clear on it, - - but after re-reading the original post I guess maybe he means it runs 'parallel' to the floor, - - I thought he meant it was running upward and was 'capped' at the floor.


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## karma_carpentry (Aug 7, 2005)

Tom -

No, I can only see one elbow - it comes in from one wall and out under the doorway, all at subflooring level. I'd have to chase it out by ripping up subfloor in the hallway. Nothing's capped within sight.

Thanks all for the advice folks -- I'm gonna sleep on it and not going to open it up unless I can be sure it's dead. I can't access two ends of the same length anywhere, so opening it up doesn't sound possible to me. I'll probably end up waiting for the plumber and he'll probably say "Oh yeah, that's a dead gaslight pipe" and cut right into it... but we'll see.

I've worked on old houses before but nothing of this size and complexity. I've always been able to trace out lines to their ends and 'get a visual' which is all I really trust, but this is just so big and full of twists and turns.

This house did have gaslighting - I found a beauty of a fixture in the attic today.

Thanks again folks, I appreciate it.


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## karma_carpentry (Aug 7, 2005)

Update:

Well, I brought in a multimeter and 150' of Romex to try to Ohm it out. I was really excited by the idea, but I soon found that everything is continous to everything else in this house. At some point it all connects, and the stack, the water feeds, and the mystery line in the floor are all freely exchanging electrons with each other.

So we sistered the levelers under this pipe. Now when the plumber gets there, he'll either determine it's dead or reroute it, and if that's not possible (because only one elbow is in our reach without significant new demo) we will end up installing extra blocking and subfloor around it and lay protection plates along its whole length... I would prefer not to do such a ridiculous thing!

Marc - to answer your question, this house has 4 kitchens and a couple old kitchen locations as well, and the basement ceiling is plastered and few pipes run below it, so I wouldn't know where to begin tracing the charged gas lines without ripping off a dozen walls and some ceilings. It's a huge house - I still get lost in it.

edit: fixed typo


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## RobertCDF (Aug 18, 2005)

Just cut it and run your blowtorch by it and see if it is dead or not:cheesygri j/k


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## karma_carpentry (Aug 7, 2005)

Well, today I went spelunking in the crawlspace, laying on planks on the 2x3 ceiling joists above the living space below, praying not to fall through, and I found a T that I couldn't see before because of blocking, with a handy plug that I slowly loosened and found no gas in it. Now that pipe is out of there!

Don't know why I didn't do this sooner. It didn't occur to me to crawl into the deadspace until today, my unconscious mind just assumed that the ceiling wouldn't support me. Frustration can get me to move.


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