Daily Code Talk — IMC 403 (Mechanical Ventilation): Mini-Series Kickoff

We’re turning Section 403 into a four-part series. This is where plan reviews slow down: misapplied people and area rates, recirculation violations, and undersized multi-zone intakes that surface at TAB and commissioning.We’ll cover 403 in four parts:• Part 1 (403.1–403.2.2): System basics — supply and return or exhaust; Group R-2/R-3/R-4 options; engineered reduction path; “do not recirculate required outdoor air”; special rules for pools and table-flagged spaces; transfer air allowances.• Part 2 (403.3.1.1 and Table 403.3.1.1): Breathing-zone foundation — pick the correct occupancy, set design occupant load, calculate people and area components, deliver to the breathing zone, and handle unlisted spaces.• Part 3 (403.3.1.1.1–403.3.1.1.2, 403.3.1.3–403.3.1.4): Zone effectiveness and system intake — apply Ez, calculate Voz and Vot for single-zone, one hundred percent outdoor air, and multi-zone recirculating systems using Ev and diversity; exhaust tie-ins; DCV floors at Ra and VAV outdoor air tracking across turndown.• Part 4 (403.3.2 for Group R-2/R-3/R-4): Whole-house outdoor air with Equation 4-9, corridor outdoor air, required local exhaust capacities, intermittent versus continuous control allowances, control labeling, and fan listing per AMCA 210–ASHRAE 51.🏗️ Why It MattersCommon redlines: using occupant density lighter than the table, recirculating required outdoor air or prohibited airstreams (pool, nail salon, note b or note g spaces), skipping Ez/Ev so the multi-zone intake is low, DCV set below the area-rate floor, and misapplied Equation 4-9 or missing local exhaust in Group R.Part 1 drops tomorrow.Comment “IMC403” for the 403 Plan-Review Starter Kit.DM “ADVISORY” for a fast ventilation-math sweep before you file.