Section C403.1/Mechanical Systems (2024 Edition Changes)
IECC 2024 Section C403 covers updated HVAC efficiencies, SEER2/EER2 metrics, heat pump provisions, and electrification readiness.
The 2024 IECC increases minimum HVAC equipment efficiency requirements over the 2021 edition, reflecting updated federal minimum efficiency standards (SEER2, EER2, HSPF2 metrics). New provisions address electrification readiness: buildings in some climate zones must provide infrastructure (electrical capacity, conduit pathways) to support future heat pump installation even if not initially installed. Economizer requirements are expanded. Heat pump supplemental heating controls must minimize electric resistance heating use.
Key changes from IECC 2021
The 2021 IECC referenced the older SEER/EER metrics. The 2024 edition requires the new SEER2/EER2/HSPF2 ratings mandated by the DOE effective January 2023. This is not just a relabeling: the new test procedures produce different numerical values. A unit rated 14 SEER might rate 13.4 SEER2 under the new procedure. Equipment schedules must use the correct metric for the adopted code edition. The electrification readiness provisions are entirely new.
What plan reviewers look for
Plan reviewers check the mechanical equipment schedule for the correct efficiency metrics (SEER2, not SEER, under the 2024 IECC). They verify the minimum values against the 2024 tables. For jurisdictions adopting the electrification readiness provisions, they check for the required electrical infrastructure to support future heat pumps. They verify economizer provisions against the expanded 2024 requirements.