Return openings sit 10 ft from open-combustion appliances in the same room, return no more than a room's supply, and are sized per instructions, Manual D or the designer.
Mechanical-room returns serve only that room, allow only sealed-combustion appliances, and keep door pressure to 0.01 in WC; closet returns are 30 cfm max with a 1.5 in undercut or 30 sq in grille.
No returns from toilet rooms, garages, unconditioned attics or direct from crawl spaces, from kitchens unless 10 ft from cooking and serving only the kitchen, from undehumidified pools, or between dwelling units.
Additions, alterations and repairs meet new-system rules without forcing the existing system to comply, and may not make it unsafe or overloaded; minor like-for-like work may be approved as built.
Searches all 4,276 IRC 2024 sections, 5,532 IBC 2024 sections and defined terms (Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 so far) and each city's local rules as they are added. Section numbers and titles from the International Residential Code and International Building Code, 2024 editions, copyrighted by the International Code Council; the IRC's electrical chapters (34 to 43) follow NFPA 70, the National Electrical Code. Requirements are summarized in our words (IRC Chapters 3 to 43, IBC Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33); read the full text at the link on each result. Local values come from each city's published documents.
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