Five More Important Changes in the 2021 International Mechanical Code

By: Reggie Hucks | Jun 07, 2021

As stated in last month’s blog, Five Important Changes to the 2021 International Mechanical Code (IMC), the new 2021 IMC has been published and is available for adoption. There are 33 significant changes to eight chapters in the 2021 edition. In this article, we will discuss changes that will impact application, installation, and energy efficiency of mechanical equipment and appliances. Let’s look at five additional changes in the 2021 IMC Code that are significantly different from the past version. 

Energy Recovery Ventilation Systems 

Energy recovery ventilation (ERV) systems save energy by using the heat from exhaust air to temper the incoming fresh air (winter operation) or to cool the incoming fresh air (summer operation). However, using an ERV system on a commercial kitchen grease hood could cause a grease fire due to grease build up in the unit. The code change allows an ERV system on kitchen exhaust systems, such as type 2 hoods, that do not handle grease or smoke. Type 1 grease hood exhaust is still prohibited. 

Duct Systems 

Current and previous code models require duct penetrations of fire barriers to be protected by fire dampers. There was one exception that allowed a completely ducted system of 26-gauge galvanized metal in lieu of a damper at the wall penetration. In the exception, no flex duct was permitted in the duct system. A new Code change allows 14 feet of flexible air duct to connect the 26-gauge supply duct to a ceiling register if they are both in the same room. If this is done properly, the damper can still be omitted at the fire barrier penetration. Flex duct or flex duct connectors can never pass through a rated wall such as a fire barrier. 

Ventilation Air Distribution 

After years of attempts to require balancing dampers in all air distribution systems, the code writers have finally made air volume balancing a requirement. Section 608.1 now requires a means to adjust air flow in all distribution, exhaust, and ventilating systems by an approved method. 

Unvented Alcohol Fuel-Burning Appliances 

Alcohol fuel-burning appliances were not addressed in previous code editions. They are now defined in Chapter 2, Definitions and have been placed in Chapter 9, Specific Appliances, Fireplaces and Solid Fuel-Burning Equipment. These appliances do not serve a heat function but are decorative. Installation instructions must be provided with the appliance installation to ensure clearance to combustibles, combustion air, and service access meets the product listing. 

Means of Egress – Machinery Rooms  

The language for machinery room egress, located in the International Building Code, is now repeated in the IMC. When machinery rooms exceed 1,000 square feet, two remote exits are required. Ample egress can protect machinery room occupants from asphyxiating, in the event of a refrigerant discharge.  


For more information or to learn more about the updates in the 2021 IMC, contact JADE Learning for courses related to HVACR.

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