목차
- Energy recovery is required on fan systems with both mechanical supply and exhaust when design outdoor-air supply exceeds the threshold in Table C403.7.1, which varies by climate zone and outdoor-air fraction: Climate zones Outdoor air (CFM) Min % outdoor air Recovery required? 3B through 8 ≥ 5,000 ≥ 70% Yes 4 through 8 ≥ 5,000 ≥ 30% Yes The device must achieve a recovery effectiveness of at least 50% of the enthalpy (or temperature, for sensible-only) difference between outdoor and return air. Exceptions cover economizer-equipped systems and cases where recovery is not cost-effective given climate and degree days.
- ASHRAE 62.1-2022 adoption by reference — ventilation is no longer optional to treat as secondary; the Ventilation Rate Procedure, IAQ Procedure, or Natural Ventilation Procedure must be demonstrated. Demand-control ventilation (DCV) expansion: spaces above 500 ft² designed for more than 25 people often mandate CO2-based DCV, trimming 15–30% of fan and conditioning energy. Enhanced commissioning: ERV/DCV systems must be verified for airflow, sensor calibration, and control sequence. Multifamily as commercial: buildings four stories or taller follow commercial paths, and the 2021/2024 prescriptive path requires ERVs in dwelling units (the performance path can trade this out via modeling).
- C403.7 mirrors the federal ASHRAE 90.1-2022 5,000-CFM / 70%-OA / 50% rule, and aligns with ASHRAE 62.1 on outdoor-air loads. The building code heat recovery mandate article lines these up against California Title 24 and EU Ecodesign. Pick a core at 70–75% effectiveness and it clears every regime at once.
- Confirm the AHU run-hours (the < 8,000 h/yr vs ≥ 8,000 h/yr split matters in the table) and fold the core into the AHU selection calculation before sizing the coil.
티he International Energy Conservation Code (IECC) is updated on a three-year cycle (2018, 2021, 2024) and is adopted — with or without amendments — by most U.S. states. Its commercial energy-recovery rule lives in Section C403.7, and it is the baseline that many state codes reference. This article summarizes the C403.7 trigger and how the 2024 edition tightens ventilation.
Energy recovery is required on fan systems with both mechanical supply and exhaust when design outdoor-air supply exceeds the threshold in Table C403.7.1, which varies by climate zone and outdoor-air fraction:
| Climate zones | Outdoor air (CFM) | Min % outdoor air | Recovery required? |
|---|---|---|---|
| 3B through 8 | ≥ 5,000 | ≥ 70% | Yes |
| 4 through 8 | ≥ 5,000 | ≥ 30% | Yes |
The device must achieve a recovery effectiveness of at least 50% of the enthalpy (or temperature, for sensible-only) difference between outdoor and return air. Exceptions cover economizer-equipped systems and cases where recovery is not cost-effective given climate and degree days.
- ASHRAE 62.1-2022 adoption by reference — ventilation is no longer optional to treat as secondary; the Ventilation Rate Procedure, IAQ Procedure, or Natural Ventilation Procedure must be demonstrated.
- Demand-control ventilation (DCV) expansion: spaces above 500 ft² designed for more than 25 people often mandate CO2-based DCV, trimming 15–30% of fan and conditioning energy.
- Enhanced commissioning: ERV/DCV systems must be verified for airflow, sensor calibration, and control sequence.
- Multifamily as commercial: buildings four stories or taller follow commercial paths, and the 2021/2024 prescriptive path requires ERVs in dwelling units (the performance path can trade this out via modeling).
C403.7 mirrors the federal ASHRAE 90.1-2022 5,000-CFM / 70%-OA / 50% rule, and aligns with ASHRAE 62.1 on outdoor-air loads. The building code heat recovery mandate article lines these up against California Title 24 and EU Ecodesign. Pick a core at 70–75% effectiveness and it clears every regime at once.
Confirm the AHU run-hours (the < 8,000 h/yr vs ≥ 8,000 h/yr split matters in the table) and fold the core into the AHU selection calculation before sizing the coil.