Significant changes to mechanical ventilation in the 2021 International Residential Code
A clarification to Section R303.1 of the 2021 International Residential Code concerns mechanical ventilation
A clarification to Section R303.1 (Mechanical Ventilation) of the 2021 International Residential Code (IRC) states that a local exhaust system is an acceptable substitute for natural ventilation in kitchens.
To provide flexibility in satisfying the ventilation air requirements, the code adds some options for mechanical ventilation. Prior to the 2012 edition, the IRC provided an option for mechanical ventilation systems capable of producing 0.35 air changes per hour (ACH) or whole-house mechanical ventilation systems where the prescribed natural ventilation was not provided. In the 2012 IRC, the first option was deleted in favor of the whole-house mechanical ventilation system covered in the mechanical provisions of Chapter 15. The 2021 code reintroduces the option for 0.35 ACH for room-based mechanical ventilation systems, which are especially useful for additions or remodels. The code also now specifically recognizes that a local exhaust system (e.g., a kitchen exhaust hood) is an acceptable substitute for natural ventilation in kitchens. This is consistent with provisions in Chapter 15 that recognize kitchens have different ventilation requirements than other habitable rooms. The intent is to clarify that local exhaust, not whole-house mechanical ventilation that could be located in a far corner of the house, is needed for kitchens to ensure that cooking pollutants generated in the kitchen are captured and exhausted at their source. The IRC sets installation requirements for kitchen exhaust but has not previously required a range hood. The intent of the change to the exceptions in Section R303.1 is to require local mechanical exhaust in the kitchen if natural ventilation through openable windows and doors is not provided.
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The 2021 Significant Changes guides are available for the International Building, Fire, Residential, Energy Conservation, Plumbing, Mechanical and Fuel Gas Codes. This valuable series can help any code user save time by zeroing in on the most critical changes in the 2021 International Codes. The Code Council’s technical experts provide summaries, analysis and graphics for these changes making them clear and easy to understand. Each edition provides a comprehensive analysis of significant changes since the 2018 edition, offering key insights into its contents and implications. Each change analysis features the affected code sections and identifies the change with strikethroughs and underlines to show modifications to the existing language. Each change is accompanied by a quick summary, detailed illustrations, and a discussion of its significance, which brings the technical jargon of the code to life in a real-world setting.