For Natural Gas Plumbing (new construction). What is the allowable or tolerable pressure escape during the test period and how long should the test period last?

For example: Original pressure during test is at 10.5 lbs. After 24 hours, it dropped to 9.75 lbs. Is this OK? My plumber said that gas line typically has only 4 ounces of pressure, is this correct?

Thank you in advance.

Low pressure gas lines typically run about 4 oz. High pressure gas lines typically run about 2#, then put pressure regulating valves at a manifold or at each appliance to knock it down to 4 oz.

To test, pump it up and use soap bubbles to find the leak. The lost air is going somewhere. Make sure all appliances are capped off. If your using a gas valve (say on a furnace) to hold back 10# of pressure, it won't work. Pressure gauge could have a small leak.

A small loss over 24 hours won't really be enough to be a huge safety issue. I suspect the plumber knows this, but it's still an excuse and should be corrected.

You could also call your local gas company, ours does new const. inspections and ask about their policy on air testing gas lines.

There are no appliances yet, this is for a new construction, and yes - my plumber used bubble test and we didn't find any leak. He thinks it's escaping from some of the caps or perhaps from the meter itself because it's such a small loss. Thank you for the advice, I'll try and call our local gas company as well.