2024 International Mechanical Code Release

In August 2023, the International Code Council (ICC) announced the release of the first few 2024 International Codes, including the 2024 International Mechanical Code (IMC). This article will review important code changes, the code adoption process, and what ICC calls “the most substantial format changes to the International Codes in 25 years.” 

2024 IMC Changes

Important Updates

Every three years, ICC introduces potential code changes and starts a governmental consensus process. There are four objectives that ICC follows during every code development cycle. These include:

  1. Recognize relevant technological developments that could impact future codes.

  2. Establish methods for open communication for all interested parties (tradespeople, lawmakers, trade organizations, etc.).

  3. Keep public officials that are relevant to the implementation and enforcement of codes actively engaged in the final determination of code text.

  4. Promote participation of all parties desiring to participate in the development process through an online submittal and voting process.

One of the biggest updates to the 2024 IMC came from a 2021 Environmental Protection Agency (EPA) rule that mandated an 85% phasedown in HFC refrigerants over the next 15 years due to their high global warming potential (GWP).

The final EPA rule now accepts six refrigerant alternatives to HFCs for new residential and light commercial air conditioners and heat pumps. These low-GWP and low-flammable alternatives are classified by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) as A2L refrigerants.

A2L refrigerants have different flammability characteristics than current A1 refrigerants like R-410A. The 2024 IMC includes several code changes that permit using A2L refrigerants for human comfort uses, consistent with industry standards, and will help to facilitate the phasedown of HFCs following EPA rules.

Other updates approved during the development process include:

  • Removal of provisions prohibiting the use of domestic ductless range hoods in Groups I-1 and I-2.

  • Group A2L and B2L refrigerants now have an identification requirement.

  • Machinery rooms containing Group A2L refrigerants have new requirements, and Group B2L refrigerants were added to the provisions.

  • Limits for the use of Group A1 and A2L refrigerants changed in high-probability systems used for human comfort, unless permitted as excepted.

  • Exhaust system common ducts serving separate dwelling units now require the common duct or shaft to be maintained at a negative pressure at all times.

  • UL 2158A Standard was added to the requirements for commercial dryer exhaust

  • Outpatient health care facilities now have ventilation requirements that match the requirements in ASHRAE 62.1-2019.

  • Addition of a new minimum landing size requirement at the roof hatch, which allows personnel to safely access the roof for repair and maintenance.

  • Addition of a new testing option for grease ductwork.

  • New steam bath requirements.

  • A new standard requirement for refrigeration systems containing carbon dioxide. 

Formatting Updates

When reviewing the code, you may notice the visual and formatting changes that are part of what ICC calls an “ongoing digital transformation.” After collecting feedback from print and digital International Code users, ICC applied substantial formatting changes to improve readability, reduce page count, and offer the same experience to print and digital users.

According to ICC, the formatting updates promote a cleaner, more modern look.

Changes include:

  • A switch from double to single column text with a modernized font to improve readability.
  • Streamlined lists.
  • Shading for table headers and notes to improve locating tables and applicable notes.
  • Expansion of the index to three columns.
  • Associated content grouping so tables and figures show immediately after the parent section.

Code change identification has also been overhauled in an effort to help users identify changes more precisely. Now, QR codes replace the marginal sidebar markings and arrows.

Scanning a QR code sends you directly to the digital version of the code change. QR codes are placed at the beginning of any section that has a technical revision. If there is no QR code, there are no technical changes to that section.

For those not interested in using the QR codes, you can manually access the code change online by entering the ID found within the QR code into your browser.


New Code Compliance Preparation

Now that the 2024 IMC is available, it must go through an adoption process. The codes that ICC creates are presented as models or templates that a local authority having jurisdiction (AHJ) — like a state, county, or city — can incorporate into its own laws. Before reviewing, adopting, and incorporating the model code, AHJs usually make changes that reflect local practices and laws.

Due to copyright law, any adopted laws that use the 2024 IMC will incorporate it by reference instead of using any code text. That means an AHJ’s adopted law will cite the title, edition, and publishing information of the 2024 IMC.

It may take some time before HVAC professionals across the country start seeing 2024 IMC changes adopted into their own local laws. Since the new code came out in August 2023, most states are still reviewing it.

Currently, 47 states, the District of Columbia, Guam, Puerto Rico, and the U.S. Virgin Islands have adopted a version of the IMC at the state or local level. But, as you can see in the image below, not all AHJs adopt the newest editions of the IMC right away.


Next Steps

While HVAC professionals wait for their AHJs to adopt a new version of the IMC, we encourage them to review the changes and think about participating in the next code development process. According to ICC, the public comment period for submitting code changes for the 2024–2026 code development cycle started on October 16 and ends on January 8, 2024.

A cdpACCESS account is required to submit code change suggestions, vote on proposed changes, or participate in the public comment period. The first 2024 Committee Action Hearing is currently scheduled for April 7–16, 2024.

As states review and adopt the 2024 IMC, we’ll work on keeping our site updated and make sure all students learn about any updated CE requirements. In the meantime, we encourage all HVAC professionals to use their cdpACCESS account and participate in the next code development cycle!


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International Code Council. (n.d.). New EPA Refrigerant Rules and their Impact on 2024 I-Codes: 

what AHJs, HVAC contractors, and others need to know. Retrieved from

International Code Council. (n.d.). New Design for the 2024 International Codes. Retrieved from

International Code Council. (2022, December 07). CP#28-05 – Code Development. Retrieved from

International Code Council. (n.d.). Code Adoption Resources. Retrieved from

International Code Council. (n.d.). 2024 International Mechanical Code. Retrieved from