Customer has 31 y/o Rheem system that operates for whole house. System was not heating due to thermostat not being wired correctly. Noticed during inspection that heat exchanger is very poor, however, no carbon monoxide was detected in home. Rust throughout furnace. R22 based system. Overall condition of system is poor. Customer was advised not to use furnace due to condition and seek options to replace system. TE not responsible for system due to age and condition of system.