Upon arrival customer er stated that heat stopped working yesterday for about 4 hours then came back on and was heating home since then. Customer still wanted to have system inspected for any potential issues. System was heating prior to arrival. Gas furnace is 13 years old and ac/coil is 19 years old. Did full inspection of system, heat exchanger is in bad shape there is a lot of rusting inside the chambers, flue pipe was changed out before due to cracking and rusting, the old flue pipe did affect the furnace before flue pipe was changed to double wall. Blower wheel was clean, blower motor capacitor tested good. Flame sensor was clean, pressure switch tube port was clean. Evaporator coil is very rusted. Went over findings with customer advised customer did not pinpoint an issue as of now with system heating, do recommend speaking with our install supervisor to receive a free estimate on replacing aged and obsolete ac unit and aged furnace due to conditions of system that could be caus