Thanks so much for the response Mr. Pope - yes, it is CSST - it looks to be about an 1.5"—I will post a pic tomorrow (Wed)…it appears to be the same CSST as installed throughout the house’s other furnace, but, the yellow sleeve was frayed from the original installation - we are being told it may not be code compliant today but we know the rest of the houses in our area were like ours and have this as original construction in 2001 (we are original owners)…we are looking to see if we are "grandfathered’ into the code from 2001 vs today’s code and simply just want to repair the frayed portion vs replacing the entire line with different material before selling the house
CSST is perfectly acceptable by most model codes. If it was acceptable at the time of construction, it’s still acceptable unless your local jurisdiction has prohibited its use. A call to the Building & Safety Department will clear it up quickly.
Codes are not retroactive (that’s the concept behind “grandfathering”).
As Bob eluded to, there are additional bonding requirements when CSST is installed. If you are in a high lightning zone (LDZ - Lightning Density Zone) you may need additional bonding of the gas lines to the residence grounding electrode.