We have a Trane XL 80 Model #TDD080R936C3, installed 12-2-96 (15 years old now). It was discovered that there is a flexible gas line connector installed inside the furnace cabinet. We were told this is incorrect. I found a reference under the International Mechanical Code that reads: 304.12 Installation at gas valve. Black Iron Pipe shall be installed at the gas valve and extended a minimum of two inches outside the gas furnace and gas rooftop unit's casing and shall be connected to an approved listed flexible gas connector.

Can you tell me if in 1996 Trane recommended installation of the hard pipe on the inside of the furnace and OK'd flexible pipe outside the furnace cabinet? Do you know of any code requirements in King County WA then and if requirements have changed since then? I sure appreciate your help!