The 2024 International Mechanical Code (IMC) is a comprehensive standard developed by the International Code Council (ICC) to regulate the design, installation, and maintenance of mechanical systems in residential, commercial, and industrial buildings. It establishes minimum requirements for safety, efficiency, and environmental sustainability, ensuring that mechanical systems meet modern performance standards.

The IMC is updated every three years to incorporate advancements in technology, construction practices, and safety protocols. These updates ensure that the code remains relevant and reflects the latest industry trends and innovations, providing professionals with a reliable framework for compliance.

The 2024 IMC is an essential resource for:

• HVAC professionals
• Mechanical engineers
• Code officials and inspectors
• Contractors and builders
• Architects and designers

Anyone involved in designing, installing, or inspecting mechanical systems can benefit from its comprehensive guidance.

The IMC combines prescriptive requirements with performance-based provisions to ensure flexibility while maintaining high safety standards. It covers critical aspects like ventilation, heating, cooling, refrigeration, exhaust systems, and fuel-burning appliances to minimize risks and optimize energy efficiency.

While the IMC serves as a model code adopted widely across the United States, its application varies by jurisdiction. Local authorities may amend or customize it to meet regional needs. Always check with your local building department to confirm which version of the code applies in your area.

The 2024 IMC introduces provisions for environmentally friendly refrigerants like Group A2L and B2L, supporting efforts to reduce greenhouse gas emissions. It also emphasizes energy-efficient designs and systems that align with global sustainability goals.

The 2024 IMC applies to a wide range of structures, including residential, commercial, and industrial buildings. It covers new construction, additions, alterations, and repairs to existing mechanical systems in these buildings.

The 2024 IMC incorporates energy efficiency requirements throughout its provisions. It sets standards for equipment efficiency, system design, and controls to minimize energy consumption while maintaining comfort and safety. The code works in tandem with the International Energy Conservation Code (IECC) to promote sustainable building practices.

The 2024 IMC is organized into several key chapters, including:

• Administration
• Definitions
• General Regulations
• Ventilation
• Exhaust Systems
• Duct Systems
• Combustion Air
• Chimneys and Vents
• Specific Appliances, Fireplaces and Solid Fuel-Burning Equipment
• Boilers, Water Heaters and Pressure Vessels
• Refrigeration
• Hydronic Piping
• Fuel Oil Piping and Storage
• Solar Thermal Systems

The 2024 IMC provides detailed guidelines for ventilation in various building types and occupancies. It specifies minimum ventilation rates, outdoor air requirements, and methods for calculating ventilation needs. The code also addresses natural ventilation, mechanical ventilation systems, and special ventilation considerations for specific spaces like garages, kitchens, and healthcare facilities.

The 2024 IMC covers refrigeration systems extensively, including:

• Safety classifications of refrigerants
• System design and installation requirements
• Piping and valve specifications
• Equipment and machinery room standards
• Refrigerant detection and alarm systems
• Emergency ventilation for refrigeration machinery rooms

The 2024 IMC includes several provisions to ensure good indoor air quality:

• Specifying minimum ventilation rates for various occupancies
• Requiring filtration of outdoor air
• Addressing contaminant sources through exhaust requirements
• Regulating the use of materials that may off-gas harmful substances
• Providing guidelines for maintaining and operating mechanical systems to preserve air quality

The 2024 IMC provides detailed requirements for exhaust systems, including:

• Specifications for kitchen hood ventilation systems
• Standards for bathroom and toilet room exhaust
• Requirements for clothes dryer exhaust
• Guidelines for industrial and hazardous exhaust systems
• Provisions for makeup air to balance exhaust airflow

The code specifies requirements for providing adequate combustion air to fuel-burning appliances. It covers:

• Calculation methods for determining combustion air needs
• Guidelines for combustion air openings and ducts
• Special provisions for large spaces and engineered systems
• Requirements for mechanical combustion air supply systems

The 2024 IMC provides comprehensive guidelines for duct systems, including:

• Materials and construction standards
• Installation requirements and support systems
• Insulation specifications for energy conservation
• Sealing requirements to prevent air leakage
• Provisions for underground duct systems
• Fire and smoke damper installation guidelines

Safety is a primary focus of the 2024 IMC, with provisions such as:

• Requirements for equipment access and clearances
• Guidelines for protecting mechanical equipment from damage
• Standards for safety controls on various types of equipment
• Regulations for handling and storing hazardous materials
• Emergency shutdown procedures for mechanical systems
• Fire protection requirements for ductwork and air handling systems

The 2024 IMC introduces substantial formatting changes to improve readability and user experience. It also includes important technical updates, particularly regarding refrigerants, ventilation, and safety measures

The 2024 IMC features a cleaner, more modern look with improved readability. Changes include:

• QR codes for easy access to digital versions of code changes
• Streamlined layout for better alignment between print and digital versions
• Reduced page count for easier navigation

The 2024 IMC introduces new provisions for Group A2L and B2L refrigerants, which are low-GWP (Global Warming Potential) and low-flammable alternatives to HFCs. These changes align with EPA regulations mandating an 85% phasedown in HFC refrigerants over the next 15 years

The 2024 IMC includes updated ventilation standards, including:

• Increased outside air requirements for dwelling units
• New requirements for exhaust system common ducts serving separate dwelling units, mandating negative pressure maintenance at all times

Safety improvements in the 2024 IMC include:

• Addition of leak detection monitoring with alarm requirements where the discharge from safety relief valves is not readily visible to occupants
• Removal of requirements prohibiting the use of domestic ductless range hoods in Groups I-1 and I-2

The 2024 IMC replaces marginal sidebar markings and arrows with QR codes. These codes are placed at the beginning of any section with a technical revision, allowing users to access the digital version of the code change directly

While this change is part of the 2024 International Plumbing Code (IPC), it's worth noting that showerhead flow is now limited to 2.0 gallons per minute (7.5 L), with performance complying with high efficiency requirements

The 2024 IMC includes several code changes that permit the use of A2L refrigerants for human comfort uses. These changes are consistent with industry standards and will help facilitate the phasedown of HFCs following EPA rules

The 2024 IMC adds new requirements for exhaust system common ducts serving separate dwelling units. These common ducts or shafts must now be maintained at a negative pressure at all times

HVAC professionals can participate in the next code development cycle by:

• Creating a cdpACCESS account
• Submitting code change suggestions
• Voting on proposed changes
• Participating in public comment periods
  The public comment period for the 2024-2026 cycle runs from October 16, 2023, to January 8, 2024

The adoption process varies by jurisdiction. While 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, not all jurisdictions adopt the newest editions immediately. It may take some time before the 2024 IMC is widely adopted