Your technician just told you that you need a new furnace because there is a hole in the heat exchanger.  Now is the time to quiz him about his findings.  Make the technician take you up in the attic and show you the hole.  Many air conditioning and heating companies are not honest and their only goal is to sell you a new furnace.  If there is a hole or a crack in the heat exchanger, then the furnace must be changed according to the American Gas Association.  Most cracks are caused by heat stress and most holes are caused by rust.  The situation that caused the problem must be addressed to