Heat Exchanger inspection for a home inspector will not likely be very involved and does not need to be with the correct tools. Most newer installations will require a carbon monoxide sensor(s) to be in the home. However while in the home a home inspector equipped with a CO Tester can check for cracks by simply running the forced air furnace be it horizontal, up-flow or down-flow and taking some readings around the burners at the inlet of the heat exchanger. Let the furnace run for some time so the exchanger can heat up and if there is any cracks the CO will want to be pushed by the air around the heat exchanger to the inlet of the burners. This may also be seen in the way of roll out wherein flames are blown back towards the inlet of the burners due to the forced air making it’s way in to the compromised heat exchanger and mixing with the flames inside the serpentine box.