2021 Uniform Mechanical Code (UMC)

The 2021 Uniform Mechanical Code (UMC®) provides comprehensive requirements for the installation, inspection, and maintenance of heating, ventilation, cooling, and refrigeration systems. Developed through the ANSI Consensus Process and designated as an American National Standard by the American National Standards Institute (ANSI), the 2021 UMC reflects current practices, technologies, and requirements in the mechanical industry.

The 2021 edition is particularly significant for its provisions addressing low-flammability A2L and B2L refrigerants, including refrigerants with lower Global Warming Potential (GWP). The code incorporates contributions from a broad range of professionals and stakeholders across the built environment.

Key Updates in the 2021 Uniform Mechanical Code

The 2021 UMC includes numerous updates and new requirements, including:

• New Appendix F – Geothermal Energy Systems
• New guard and rail requirements for equipment and appliance installations on roofs
• Updated ventilation requirements for transient and nontransient occupancies
• New residential ventilation requirements addressing indoor air quality
• Revised requirements for air ducts, including factory-made air ducts and dampers
• New provisions for factory-built grease ducts
• Updated refrigeration system requirements, including pressure-limiting devices and hydrostatic expansion
• Revised sizing requirements for natural gas and propane piping systems
• Updated pressure-rating requirements for hydronic piping applications
• New requirements for fuel gas piping appliance shutoff valves, test pressure, and overpressure protection
• New tube fastener provisions for radiant heating and cooling systems
• New requirements for residential compressed natural gas (CNG) fueling systems
• New fire-extinguishing equipment and carbon monoxide detection requirements for exhaust systems