Went to a clean and check in an older house in a golf course subdivision. The house was over 5,000 sq. ft. and had 3 Lennox G11 Conservator 80% furnaces from 1980-1981. They also had 3 A/C, 3 General humidifiers, and 3 Lennox EAC units.
All 3 furnaces had cracked heat exchanger panels. All panels. 2 had panels that looked like this:
The holes are baseball sized.
Oh, and I bet these A/C units work great!
The dude just bought the house and wants everything replaced now. WooHoo lots of commissions for me.