Our old system was installed in the early 70s. With todays temps it just could not keep up. We replaced the furnace (4 ton 88000 btu 80 afu) AC (2 speed 95 SEER)and all ducting with a Lennox system. The old ducts were rusted through. Its 104F outside today and 75F in the house. on an day like today the old unit could not get the house below 82. I'm loving it