Section 403.3/Outdoor Air Rate (2024 Edition)
IMC 2024 Section 403.3 covers updated outdoor air rates aligned with ASHRAE 62.1-2022 and expanded DCV requirements.
The IMC 2024 updates Table 403.3 outdoor air ventilation rates to align with ASHRAE 62.1-2022. New space categories are added and some existing rates are revised. The two-component approach (per- person rate Rp plus per-area rate Ra) is maintained. The 2024 edition adds explicit requirements for demand control ventilation (DCV) in high-density spaces, aligning with the energy code requirements. The outdoor air calculation must account for system ventilation efficiency for multi-zone systems.
Key changes from IMC 2021
The 2021 IMC referenced ASHRAE 62.1-2019 rates. The 2024 edition references ASHRAE 62.1-2022, which revised rates for some space categories and added new categories. The DCV provisions are more explicit, requiring CO2-based DCV for spaces with a design occupancy exceeding 25 people per 1,000 square feet served by systems over 3,000 CFM. System ventilation efficiency calculations for multi-zone systems are more explicitly required.
What plan reviewers look for
Plan reviewers check the ventilation schedule against the 2024 Table 403.3 rates. They verify DCV is provided where required by the expanded 2024 provisions. They check that the system ventilation efficiency calculation is provided for multi-zone VAV systems. They verify the outdoor air rates match the correct ASHRAE 62.1 edition.