2021 Uniform Mechanical Code Soft Cover with Tabs

The 2021 edition of the Uniform Mechanical Code (UMC®) represents the most current approaches in the mechanical field. It is the seventh edition developed under the ANSI Consensus process and is designated as an American National Standard by the American National Standards Institute (ANSI).

Notably, the 2021 UMC is among the first codes in the industry to address specific provisions for low-flammability refrigerants, including A2L and B2L classifications, supporting the transition to low Global Warming Potential (GWP) refrigerants. Contributions to the development of this code were made by every segment of the built environment, including consumers, enforcing authorities, installers and maintainers, labor organizations, manufacturers, research, standards and testing laboratories, special experts, and end users.

The UMC provides comprehensive requirements for the installation and maintenance of heating, ventilating, air-conditioning, and refrigeration (HVACR) systems, while still allowing flexibility for innovation and emerging technologies. 

Key changes in the 2021 UMC include:

• New Appendix F addressing geothermal energy systems

• New guard and rail requirements for equipment and appliances installed on roofs

• Updated ventilation requirements for transient and no transient occupancies

• Enhanced indoor air quality ventilation requirements for residential occupancies

• Revisions to air duct requirements, including factory-made ducts and dampers

• New provisions for factory-built grease ducts

• Expanded requirements for refrigeration systems, including pressure-limiting devices and hydrostatic expansion protection

• Revisions to natural gas and propane piping sizing requirements

• Modifications to pressure rating requirements for hydronic piping systems

• New fuel gas piping requirements, including appliance shutoff valves, test pressures, and overpressure protection devices

• 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