I am obtaining estimates to replace the furnace (forced air) and A/C for our house. One of the estimaters told me that with the newer more efficient furnaces, it will be be required to have the chimney lined with metal since metal conducts heat better that a clay pipe liner. He said that without the metal liner, the furnace exhaust would condense prior to making it out ot the chimney, causing eventual deterioration and collapse of the chimney. Is there anyone out that that can comment on this? Is the metal liner needed for permitting? I live in Morris Township NJ.