: Zone → System Outdoor Air
Plain English: Plain English Highlights
403.3.1.1.1: For each zone, size OA from occupancy type and air-distribution effectiveness.
403.3.1.1.1.1 (Vbz): Vbz = Rp·Pz + Ra·Az (Rp/Ra from table; Pz = people; Az = net occupiable area).
403.3.1.1.1.2 (Ez): Pick Ez by config: ceiling cool 1.0; ceiling warm/ceiling return 0.8; floor warm/ceiling return 0.7; displacement (low-velocity cool, stratified) 1.2 when criteria are met.
403.3.1.1.1.3 (Voz): Voz = Vbz / Ez.
403.3.1.1.2 (System OA): Sum/correct zones by system type.
403.3.1.1.2.1 (Single-zone): Vot = ΣVoz.
403.3.1.1.2.2 (100% OA): Vot = ΣVoz.
403.3.1.1.2.3 (Multi-zone recirc): Zp/Ev/D method:
.2.3.1 (Zp): Zp = Voz / Vpz (Vpz = occupied-min primary airflow).
.2.3.2 (Ev): From table using Max(Zp).
.2.3.3 (Vou): Vou = D · ΣVoz, with D = Ps/ΣPz.
.2.3.4 (Vot): Vot = Vou / Ev.
403.3.1.2 (Exhaust): Provide table exhaust; transfer air OK where footnotes allow.
403.3.1.3 (DCV): May modulate by occupancy but not below Ra during occupancy.
403.3.1.4 (VAV controls): Must maintain OA across turndown - fixed damper alone isn't compliant.
Calculation Check: Step-by-Step (mirror on M-601)
Table → Vbz: choose Rp, Ra; set Pz, Az → Vbz.
Delivery → Voz: pick Ez → Voz = Vbz/Ez.
System:
Single-zone/100% OA → Vot = ΣVoz.
Multi-zone: set Vpz → Zp → Ev; find Ps, D; Vou = D·ΣVoz; Vot = Vou/Ev.
Coordination Check: Frequent Redlines
Vbz shown but Ez not applied (no Voz).
VAV minimums in math ≠ BAS setpoints.
Wrong Ps or missing D in Vou.
Claiming Ez = 1.0 for warm ceiling supply without ≤15°F ΔT and 150 fpm throw to 4.5 ft.
Calling "100% OA" in calcs but scheduling a mixed-air AHU/RTU.
Code Path: Where to Show It (sheet map)
M-601 (zones): Occupancy, Rp/Ra, Pz/Az, Vbz, Ez, Voz, Vpz, Zp.
AHU/RTU block: Max(Zp), Ev, D, Vou, Vot; DCV logic; VAV occupied minimums.
M-002 / M-603: OA tracking across turndown, Ra floor, sensors/alarms.
M-101+: Diffuser types/temps that justify Ez; tag exhaust/recirc limits.
Field Tip: Field Tips
Lay out diffusers to earn Ez ≥ 1.0 (or displacement 1.2 when criteria apply). If you can't defend it, reviewers default to 0.8.
Freeze VAV occupied minimums in schedules and sequences - your Zp/Ev math depends on them.
For swing-use rooms, base Pz on the highest concurrent load or attach approved stats.
Using transfer air to meet exhaust? Show the path, door relief, and that the Ra floor still holds.
Want a fillable Vbz/Voz/Zp/Ev/Vou/Vot worksheet plus paste-ready DCV/VAV control notes? Comment IMC403.
DM ADVISORY for a fast ventilation math check.
Masterbuild QA Lens
Ventilation posts should translate code language into a permit-ready airflow story: occupancy, outdoor air quantity, intake location, exhaust relationship, controls, and any exception being used.
Drawing / Submittal Check
Verify the drawings show occupancy basis, ventilation method, outdoor air path, intake and exhaust separation, transfer air assumptions, controls, and schedule values that match the calculation.
Common Review Risk
The common review risk is an airflow value without a traceable basis. Another risk is showing outdoor air on a schedule while the plan, intake location, or control sequence tells a different story.
When To Escalate
Escalate for healthcare spaces, high-occupant-load areas, unusual contaminants, existing air handlers with unknown outside air capacity, or any project where pressure relationships matter.
Load Assumption Check
For load-driven decisions, make the assumptions visible: weather basis, orientation, envelope, occupancy, ventilation, equipment gains, and any existing-building limitations that affect capacity.
Ventilation Coordination
For outdoor air and exhaust locations, confirm separation distances, source hazards, rain/weather exposure, maintenance access, and the control sequence that proves the intended airflow during operation.