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Old 09-11-2011, 02:21 PM   #1
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purging gas in the pipe


Hi all,

I am planning to convert our electric cooktop to a gas one. Our gas meter is right outside the kitchen. I talked to a city inspector and he said I can put a T before the pipe enters the house, run it through the crawl space and then get it into the kitchen. Probably the whole thing will be an addition of 20-30 feet of gas line.

I presume there will be some gas left inside the pipe even after I turn off the main valve. How can I safely purge the gas line? Also what would be the best practice for cutting a straight supply line and inserting a T? I used sharkbites to do that on our water supply lines, but I think that won't work with gas pipe. I would very much like to hear your suggestions.

Thank you very much,
A.

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Old 09-11-2011, 04:45 PM   #2
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purging gas in the pipe


The correct way to purge gas piping under 4" is to use either a purge hose to the outdoors terminating at least 10' from any vents or building openings, or an approved purge burner. I'm sure all my fellow gas fitters follow the code precisely when purging .

As for cutting in a tee, shark bites are definitely out of the question. Depending on how your current gas system is run, it may be as simple as removing the outlet of the meter and replacing the 90 with a tee, cutting the pipe and adding new pipe with a union, or more extensive re-piping.

Also, I have a few of questions for you: Are you allowed to pull a permit and do your own gas work? Do you know how to size a gas piping system (not just a pipe, but the system as a whole)? Do you know how to test the new line, as well as the old line if you've disturbed it in any way? although I am well aware that this is a DIY site, you and your family may be better off playing it safe and calling in a pro; this isn't water you're playing with here.

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Old 09-11-2011, 06:30 PM   #3
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purging gas in the pipe


Just shut off, and what little bit left in the piping, will either escape out of the water heater, furnace if the pilot is on, or will leak once you open the piping. Just remember to not smoke or use a open bulb when opening the piping. I have done it plenty of times, and have no problems.

Sharkbite fittings do not belong on gas piping. The parts you can get at Ace Hardware, Lowe's, Home Depot, but the problem is, that if you do not know the length you need, it would be cheaper to just have a plumber do the work. They will also be able to cut the black iron and thread on site.
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Old 09-11-2011, 07:01 PM   #4
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purging gas in the pipe


I just re-read the OP and realized that he was talking about BEFORE he re-pipes, lol. I would just crack the meter spud to bleed down the line pack, then just make sure you leave a window open while opening up any gas lines inside. My previous advice was for AFTER the new lines were installed.

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Old 09-11-2011, 08:16 PM   #5
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purging gas in the pipe


That would be the way I would do it, especially if playing in a crawl space. As quick as most burns off during the shut off, there is very little in the line to really do much, just pressure.
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Old 09-11-2011, 11:46 PM   #6
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purging gas in the pipe


Hi folks,

Thanks for the responses and suggestions. Even if I have someone do the job for me I still want to learn as much as I can.

I tried to modify a pipe sizing chart I found on the internet, and work out the flowchart they provided. I think 1/2" pipe should be enough for adding a 45k cooktop that will located less than 25 ft from the meter. And I don't think the addition would starve the other gas appliances.

My approved city permit clearly states "adding a new gasline to kitchen to install gas cooktop". I also indicated that I will be doing work myself. So, I should be good on that front. Whether I will feel confident enough to do it is another issue, but still as I mentioned I would like to learn as much as possible.

I was planning to buy the black pipe at HD, have them thread it in store and install it myself. I understand I need to use a pipe putty seal the joints and then screw it, but is there any soldering associated?

Thanks again for the answers.
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Old 09-11-2011, 11:57 PM   #7
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purging gas in the pipe


No putty and no soldering. There is a brand pf pipe sealant called Rector Seal at The Home Depot. It is also known in slang as pipe dope. Under the metal lid is a brush attached to spread the "dope" onto the threads. Try to not get any inside of the pipe as that eventually will lead to blockage.

We use Rector Seal, also sold at specialty hvac supply houses, for all things gas line in the hvac field such as new gas lines, the same 1/2" black steel as what you'll be using, and gas cocks on furnace change outs.

Should cost you under $10.
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Old 09-12-2011, 12:06 AM   #8
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Old 09-12-2011, 12:32 AM   #9
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purging gas in the pipe


Keep in mind, that you have to put in a T at the turn for the line going up, for a "Crud trap". That means if anything goes through the line with the flow, it will drop down into the leg with a aprx. 8 inch or so piece with a cap on it. Mine, they just used an elbow with a cap on the end, off of the t.
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Old 09-12-2011, 12:34 AM   #10
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Thanks Doc Holliday!

Also does people have an opinion against buying pipes from HD (or other major hardware stores)? Some people say that the pipes are bad and that they didn't make the threads properly....
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Old 09-12-2011, 12:48 AM   #11
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purging gas in the pipe


The only problem is those people that take advice from the retail store drone, then come here and they have to be walked through to undo what the "expert" told them how to do it. Do not get me wrong, there are some that work retail that are retired and do this stuff to get out of the house. But, when you get some pimply faced kid telling you how to do plumbing, electrical, construction, you tend to let if fall on deaf ears.

You are doing everything correctly, by coming here and asking questions, so all you have to do, is get your materials list, walk in and buy the stuff, go home and have a soda or iced tea, before diving into the job. Worst thing is, the trip will cost you a total of six trips, and in the process of doing things, you will suddenly realize when you are under the home, that now you have three more jobs to correct. That makes up for either a very long week, or a weekend wasted in fixing everything before Winter sits in.

Leave the electric for the stove, just place a lockout on the breaker, when you shut it off. You can get the lockouts at Home Depot, just get the panel manufacturer, so you can get the correct part.

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