Home inspection on one system, 2 zones, located in the attic. Checked system in heating and cooling, customer replaced filter (16/25/1). Drain line is cleared. Heat exchanger has some heavy hot spots, no in line switch do the drain line and system is 4.0 tons, with 2 zones and no bypass, to relief the pressure , and it’s a single speed furnace. System is 13 years old (ac is 5 years old) and heat exchanger is compromised. Sent estimates for potential repair (not recommend due to the age and conditions). At this age and conditions, the best option would be to upgrade the furnace (at least), for a variable speed and install a bypass to the system, as well. Set a lead to quote upgrading for Monday after 9am.