What are the Omaha, Ne Building codes for replacing an old furnace to a 95% efficient unit?

Were replacing an old furnace to a 95% efficient and we herd that we had to put in a chimney liner since only our water heater will be using the chimney and then we herd that we had to put in a liner only if the chimney was on the outside of the house which ours is not.....so if any one knows whose right or what the code is that would be helpful, thanks