Arrived onsite to customer having issues with 30 year old furnace, looked at existing venting and found it to be compromised of ABS piping. Manufacturers have never approved this style of piping in this application. Exhaust piping was within twelve inches of exhaust piping and was actually above the exhaust. Gave customer pricing for diagnostic work but did not recommend we go that route and recommended replacement of existing venting system as well as replacement of furnace due to age and condition . Customer signed for two stage upgraded option of furnace with request that work be performed on April 28. Customer had noted while onsite that we had been out and fixed a gas leak “on a piece of tubing that was left hanging†after looking through history and calling previous techs, we came to the conclusion that this was what barren had reported and that they solved the issue. Documented size of furnace and measurements of cabinet, will return at later date to complete work.