Protected flex gas line entering furnace cabinet

Older home with a flex gas line going through the furnace cabinet, with ~1/2" thick protective foam sleeve around that area of the flex line.

Would you call that out and insist on rigid piping, or is that okay?

Fishing for some kind of manufacturers documentation or code. I’m looking, but appreciate help.

This has been discussed on this forum a few times. You left out some important information.

Waiting for the inspectors that inspected a 20 year old furnace with the same “defect” and called it out. In 3,2 and 1….

thanks, your post from march was exactly what i was looking for.

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You should link to that post here so that future inspectors finding this thread aren’t left hanging. :ok_hand:

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Good point, Here’s Martin’s post from this thread

I bet most gas appliances will explicitly spell it out so Ill try and find manufacturer’s documentation if I ever encounter this again.

I happened to find an AC low voltage wire recently that was strained against an unprotected opening and was starting to get damaged… part of me didn’t actually believe that happens until I saw it!

I find it hard to believe the vibration could cut through foam insulation and the metal flex connector, but I guess there is some chance that the insulation/grommet get displaced after installation… maybe some manufacturers do recommend against that?


I would bet you $100 if you took a piece of thin sheet metal and rubbed it against an appliance connector flex gas hose or an NM cable (like a saw) you would break thru in less than an hour. A grommet would likely be helpful or even preventative.

I was in an attic a few weeks ago, the air handler was out of balance ever so slightly causing a steady vibration. The vibration could likely cut thru most things.

Might as well as had one of these, the only difference is how long it might take.



Yea you’re right, definitely possible. The thing with the foam insulation is it would have to be strained pretty hard against the opening for what I would think is years to cut through everything. Maybe 10 lbs+ of force the whole time? Otherwise it would probably just make a little indent/rubbing in the foam.

Maybe something falls on it and you don’t notice. It’s possible.

That’s just speculation about the physics of it, though, I’ll look up the make and model to back me up and recommend they consider installing rigid piping in the future. :+1:


If the furnace vibrates and an appliance connector is attached to it, they both vibrate at the same rate.
If the connector is as tight as a guitar string that’s a different matter.

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Physics. “Resonance” Resonance occurs when, two interconnected objects, in this case the CSST and Furnace cabinet, share the same vibrational frequency.