Exhaust Systems
What Candidates Must Know
Exhaust questions center on what must be exhausted, how much, and where it terminates. Understand that certain occupancies and operations require local exhaust at the source, that exhaust systems serving hazardous or grease-laden air must be independent of other systems, and that discharge points must be located away from openings, intakes, and property lines. Know the concept of make-up air: an exhaust system cannot depressurize a space to the point of backdrafting fuel-burning appliances.
Domestic kitchen exhaust, commercial kitchen hood exhaust, and bathroom/toilet exhaust each have distinct rules. Commercial cooking exhaust involves hood types, grease filters, duct clearance, and fan location; residential kitchen exhaust is far simpler but still must terminate outdoors. Clothes dryer exhaust has its own limits on duct length, fittings, and termination.
Traps
Questions frequently test termination: exhaust must not discharge into an attic, crawl space, or within a prohibited distance of a window, door, or outdoor air intake. Another trap is combining exhaust from incompatible sources into one duct. Also watch for the assumption that a recirculating filter satisfies an exhaust requirement - it typically does not where source capture is mandated.
Rule of Thumb
If the airstream contains grease, moisture, hazardous fumes, or biological contaminants, keep it in a dedicated system that terminates outdoors, and provide make-up air so the space does not go negative relative to the combustion appliance zone.
Worked example: A bathroom fan ducted into the attic soffit fails: exhaust must terminate outdoors, not in an enclosed space. Correcting it means routing the duct to an exterior wall or roof cap with a backdraft damper, keeping the run short and insulated where it passes through unconditioned space.