Positive pressure systems have an advantage when detecting hot spots, insect activity, mold and moisture condensation on the grain surface, because the observer enters the bin from the top and can easily test air temperature. The top of the grain is last to cool or warm and is easiest to visually inspect for problems. To check positive pressure systems, feel the grain and all surfaces for moisture accumulation, crusting, sticky or frozen grain. Smell for musty odors. The use of metal rods and probes is beneficial in shallow bins.
Electronic temperature sensing cables are helpful in large, deep storage structures.
Temperature-sensing cables accurately trace cooling or warming fronts and aid in detection of hot spots. High or low airflow rates work equally well, depending on the system. Negative airflow or suction systems move grain-tempered air down through the fan. Temperature and moisture deviations must be observed in the fan exhaust zone. With this system, the last grain to cool is next to the bin floor.