70% is the passing threshold. You must achieve at least 70% correct to renew, which means demonstrating a solid level of retained knowledge without demanding near-perfect performance. This level balances ensuring competency with practicality for renewal cycles. A lower mark would weaken the standard, while a higher mark would be unusually stringent for renewal exams, so 70% is used as the standard threshold.

The purpose of a grease filter differential pressure gauge is to monitor how dirty the grease filter is by measuring the pressure difference across it. As grease accumulates on the filter, it becomes harder for air to pass through, so the pressure before the filter rises relative to the air after it. When this pressure difference reaches a set point, it signals that the filter needs cleaning or replacement to restore proper airflow, protect the exhaust fan from strain, keep energy use efficient, and reduce fire risk from excessive grease buildup. This tool isn’t about room humidity, not used to regulate air speed directly, and not for testing electrical continuity.

When ductwork is undersized for a given exhaust rate, air faces more resistance as it must pass through a smaller cross-section and through fittings and bends. That extra resistance shows up as a higher static pressure that the fan has to overcome to move air. If the fan can’t increase its pressure enough to push the same amount of air, the actual airflow drops. The system then consumes more power as the motor works harder to overcome the added friction, which means higher energy use. This scenario also tends to bring about performance problems like louder operation, poorer capture of grease and smoke, and potential reliability issues. So the key consequence is higher static pressure, reduced airflow, increased energy consumption, and possible performance problems.

In solid-fuel cooking exhaust systems, the residues come from the fuel and cooking process, leading to ash, creosote, and grease deposits. Ash is the solid residue left after burning solid fuels like wood or coal and tends to accumulate in ducts and on surfaces. Creosote forms when wood smoke condenses on cooler duct surfaces, creating a tar-like, flammable buildup that can collect over time. Grease can also deposit from cooking fats and oils, especially where air streams carry particles and vapors from cooking operations, leading to sticky coatings inside the hood, ducts, and fans. This combination of ash, creosote, and grease is distinct from dust and lint, which come from exterior sources, water vapor (which is a normal component of exhaust rather than a buildup), or mold growth (which requires persistent moisture in a different context).