After installing some new CSST with black iron end points and pressure testing at 5 PSI, is it bad to lose 1/10 of a PSI (0.1 PSI) in 24 hours?

I cannot identify any leaky joints with solution and I've seen claims that 1 PSI in an hour is an incredibly tiny leak so could a tenth PSI drop be just an error in temperature change?

FWIW, the old gas line is still in use and I'm prepping for a weekend cutover from the old to the new lines.

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    I'm not a pro, but it seems like that could be attributed to a temperature swing.
    – isherwood
    Sep 25, 2020 at 17:58
  • @isherwood It pains me to ask and I think I know the answer but if 0.1 PSI is lost every 24 hours for several days then is that more telling of a leak?
    – MonkeyZeus
    Sep 25, 2020 at 18:06
  • If the ambient temperature is stable and the pressure keeps dropping indefinitely, I suppose so.
    – isherwood
    Sep 25, 2020 at 18:09
  • I think this older thread about gas line testing will be very helpful. Check with your local building inspector and your CSST manufacturer about the correct test pressure in your area. diy.stackexchange.com/questions/24835/… Home Flex, a maker of CSST, also sells a 15 PSI pressure test gauge. Sep 25, 2020 at 18:20
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    @EdBeal Additionally, natural gas runs between 1/4 - 1/2 PSI so a 5 PSI test is 10-20x operating pressure.
    – MonkeyZeus
    Sep 25, 2020 at 19:18

2 Answers 2


Home Flex's CSST manual http://homeflex.com/downloads/HOME-FLEX_Installation_Manual.pdf tells you to test at 150% of the product's operating pressure. A good rule of thumb is always check the product manual first.

When people say 20% of a gauge's capacity, they don't mean over-pressure the gas pipe system; they actually mean get a different gauge if you need to. Don't, for example, use a 90 PSI gauge to test a 3 PSI gas system; it's not designed to be sufficiently accurate for the test. The reason people say test at minimum 20% on the gauge is the NFPA 54 fuel gas code § says shall have a range such that the highest end of the scale is not greater than 5 times the test pressure. In any event, I believe you have the correct gauge for your project.

Regarding the test duration, your local building official is the authority on this; but NFPA says for a residence the test duration shall be a minimum of 10 minutes. The duration of the test shall not be required to exceed 24 hours. It further says Any reduction of test pressures as indicated by pressure gauges shall be deemed to indicate the presence of a leak. Sucks, right? The better your equipment and the more diligent you are, the more likely you chase a ghost, because the code is non-specific.

That's why I'm suggesting ask your building inspector. He or she will probably tell a story about some local system they can't believe never exploded, and tell you the 0.1 PSI is okay. Nobody here wants to be the one to say that! :D

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    I agree Jeff but different counties have different tests as I mentioned ours uses 25 or 30 And the inspector marks the gauge when he goes in and checks it after verifying shut offs venting and fresh air supplies meet minimum code takes all of 10-15 minutes, any change and it won’t get the green sticker allowing the gas company to set a tank or connect natural gas.
    – Ed Beal
    Sep 25, 2020 at 19:58
  • I have heard that testing of a whole system of new installed black steel gas pipe systems was done at up to 30 psi with compressed air to actually cause leaks to occur in defective fittings or pipe. Testing of CSST would not be at anywhere near such pressures. May 13, 2021 at 21:24


Use a manometer and get on with your life.

After switching to the new gas lines and losing some sleep over this issue I finally decided to be okay with the situation for the fact that I used to get whiffs of gas/mercaptan with the old system but my new system has no trace of smell.

Eventually my friend came over with his manometer and we properly tested my gas lines and found no leaks.


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