I'm finishing my basement ceiling which includes building a bulkhead around ductwork, plumbing and two CSST gas lines. When the house was built (2002) the contractors used just enough of the CSST to get from point A to point B pinned to the underside of the ceiling joists. For the most part I'm able to tuck the lines inside the bulkhead for the length of the room, as opposed to having them run just above the drywall. Everything would work great if one of the lines was just a bit longer. (See attached photo.)

Shouldn't I be able to splice in 4-5 feet of CSST to make it fit? Information seems scarce on this but some sources seem to say (according to codes) that you can't "splice" CSST gas lines -- that it has to be one continuous run. That seems odd but I can't find anything saying that splicing is just fine. I know my stuff when it comes to carpentry, plumbing and electric, but have no experience with gas lines. I'm not opposed to bringing in a professional to make this happen but wanted to see what options are available. Any help greatly appreciated!

I need the CSST line to follow the path of the white PVC drain pipe.


To close this out, I had a friendly, professional, licensed plumber come out and make the change and it set me back all of $110 + a $20 tip. In retrospect, there was no reason to be concerned about cost and every reason to pay a professional. Sharing this in case it's helpful for someone else facing a similar situation.

Editing to add details: The plumber used all existing lines. He added a few inches of slack by connecting to one of the manifold fittings that was just a tad closer. I'm not certain, but he may have also swapped out the "short" line with an existing line that was just a tad longer.


Some day, possibly years from now, you are going to become concerned about the smell of gas in your house. This can happen in any house, no matter how well maintained.

If you take the trouble to install a continuous CSST line today, then on that troublesome day, when you start to track down the source of the smell, you will know it can not be the splice you installed in 2021 because you didn't do that.

  • You certainly can't argue with that! My plan, though, was to make sure the splice is right next to the manifold in an unfinished area. It would never be out of sight. Feb 28 '21 at 1:15

I don't know if spliced joints meet code.

However, physically splicing CSST is clearly trivial, as even big box stores list brass unions with ¾"x¾" and ½"x½" sizes. Here's Home Depot's ¾"x ¾" one:

enter image description here


Whether or not YOU can do it depends on your local ordinance.

Are you HOME-FLEX CSST certified?

Are you prepared to pressure test that line with a gauge (okay-ish) or manometer (best) after completing your splice? You cannot test CSST connections using soap bubbles, fyi...

Quite honestly I would be much more worried about:

  1. Bonding - I don't see a clamp; hopefully it's just out of sight!
  2. Too much jacket removed- instructions state to remove only 2 valley's worth
  3. Kink? That bend radius looks far too tight. Don't try unbending it though, you could make things worse.

enter image description here

  • I very much appreciate your answer and additional input. Overall, I wanted to see if adding just a smidge of line would require hiring a pro. I take the answer to be a resounding YES. I suspected as much but wanted to make sure. Regarding your other points... Sheathing does seem jacked up. I wonder if the code changed since it was installed. Also, I've never been able to locate where the system has been bonded. Both of those reasons have underscored the need to call in someone who knows what they're doing. Regarding the third point, the line isn't kinked. That's a shadow. Thanks! Mar 14 '21 at 22:15
  • @LeftHandLuke Adding a smidge of CSST line is a trivial amount of labor. The real question is whether or not you're equipped to properly test the two new points of failure after performing the work. I'm not sure what code has to do with following the CSST instruction manual. Even stainless steel can rust so the more of it you have covered by the yellow jacket, the better. There is zero benefit to exposing more than necessary. The installer and inspector apparently didn't get that far in their thought process.
    – MonkeyZeus
    Mar 15 '21 at 12:34

Instead of worrying about CSST splices or extra-long csst pipe, why not just extend your black steel delivery pipe t>o within the required distance of the appliance?

  • 1
    Thanks for the suggestion. I don't think that would have been an option. The appliance in this case is the kitchen range upstairs. The CSST runs from the manifold, across the basement ceiling, then straight up through the kitchen floor where it connects to the floor flange. There's no slack to be found at that end. Ultimately, the plumber was able to find slack by rearranging lines back at the manifold (and he may have also swapped some existing lines to make the best fit). Mar 20 '21 at 14:47

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