/ Hub · IMC Chapter 4 · Ventilation
Outdoor air is a drawing problem, not a note that says “per code.”
IMC Chapter 4 decides whether a space gets outdoor air by occupancy table, by exhaust, or by a healthcare standard. Masterbuild puts the method, the numbers, and the intake locations on the M-sheets so plan review is not guessing.
What the drawings should identify
- Occupancy category and area for each ventilated zone — not a single building-wide cfm
- People outdoor-air rate, area outdoor-air rate, and the resulting breathing-zone outdoor air
- Whether ventilation is mechanical, natural, or a combination, and why that method is allowed
- Intake locations versus exhaust, plumbing vents, loading docks, and kitchen terminations
- Makeup air for exhaust that is not optional (kitchens, dryers, garages, hazardous processes)
- Controls that keep ventilation running when occupancy assumes it is running
- The exception path: IMC 407 / ASHRAE 170 for ambulatory care and Group I-2
- IMC 401.4 outdoor-air intake location · IMC 402 natural ventilation.
- IMC 403.3.1.1 Vbz → Voz (Ez).
- IMC 401.2 natural vs mechanical path · 403.3.2 Equation 4-9.
Where Miami sets lose weeks
Table 403 used as a slogan
A schedule that says “OA per code” without occupancy, area, and people is not a calculation. Reviewers ask for the math because the math is the code path.
Intakes that clear the wall but not the grease exhaust
Kitchen and garage terminations eat outdoor-air intake locations. See the kitchen hub and garage ventilation hub.
Healthcare treated as an office
Ambulatory care and I-2 are not Table 403 rooms with nicer finishes. They are an ASHRAE 170 problem. See healthcare ventilation.
Educational outdoor-air estimator
Run occupancy, area, and optional headcount against IMC Table 403.3.1.1 educational rates. It returns breathing-zone outdoor air (Vbz), not a sealed design.
Open the outdoor-air estimator
Daily Code Talk on this hub
- Chapter 4 kickoff — ventilation
- IMC 403 mechanical ventilation series
- IMC 401 general ventilation
- IMC 402 natural ventilation
- IMC 407 ambulatory care / Group I-2
- Free Chapter 4 ventilation fundamentals (PDF)
- Ventilation & Special Exhaust Field Guide — paid working system
Is Table 403.3.1.1 enough to size outdoor air for a Miami TI?
It is the starting math for many occupancies, not the whole design. System outdoor air can increase after zone air-distribution effectiveness, multiple-zone correction, exhaust makeup, and local amendments. Healthcare follows ASHRAE 170 / IMC 407.
What to send
Architectural plans with occupancies and areas; existing HVAC information; exhaust that must be made up; permit comments if any. Restaurants: add the equipment schedule.
Send the occupancy plan
Areas, occupancies, and whatever HVAC already exists. Masterbuild will say whether this is Table 403, an exhaust-makeup problem, or a 170 path.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval.