I have a friend who is going to purhcase a used home approximately 20 years old. He asked me to inpsect for structural integrity and I did. I looked over the Heat Pump and furnace and they are both original to the house (20Years Old). I suggested he have an HVAC contractor inpsect for him, but I am curious I would have to think he would be on borrowed time with a 20 year furnace and heatpump. What would a reasonable life expectancy be for the average unit. I really do not know how well they were maintatined either. Thanks.