I have a 26 year old 4 ton carrier heat pump that the heat has been disconnected and only operates as the condensing unit. I have a 12 yr old gas furnace that works fine and has a new blower, induction fan and hot surface igniter. Question - I was planning on only replacing the HP w/ a new 4/5 ton lennox xc 15 but after reading some of these posts it sounds like some of this new equipment can be tough to install properly and I may have better results if I install a completely new AC and furnace and get the variable motor ect. I dont really want to spend the extra $ for the furnace but I am going to have new duct installed when i do the AC so whats a few more dollars when I plan to be in this house for a long time. Thoughts? Thanks