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This is a new code for the IMC
IMC 501.6 Common ducts
The discharge from exhaust fans serving separate dwelling or sleeping units shall not be connected to a common duct or shaft, except where the common duct or shaft is maintained at a negative pressure.
Insight:
The proposed addition to the 2021 International Mechanical Code, section 501.6, seeks to address the issue of common exhaust ducts in buildings with separate dwelling or sleeping units. According to the proposal, exhaust fans serving these units should not be connected to a common duct or shaft unless it is maintained at a negative pressure. This is to prevent backflow, where the exhaust air from one unit could enter another unit if the fans are not running simultaneously. The current backdraft dampers in common exhaust systems have significant leakage rates, making it possible for odors, smoke, pathogens, and chemical irritants to transfer between units, which is highly undesirable. The ICC Plumbing/Mechanical/Gas Code Action Committee (PMG CAC), which aims to improve and enhance International Codes, submitted this proposal after several virtual meetings with interested parties who provided input on the issue.
The committee's reasoning for accepting the proposal is that positive pressure in exhaust ducts can cause airflow from one fan to leak through another non-operating fan, leading to potential contamination between units. To ensure safety and hygiene, maintaining a negative pressure in common exhaust shafts is crucial. This proposal will likely increase construction costs, particularly in scenarios where the cost of additional roof or wall penetrations is higher than combining ducts into a common system. Despite the potential for increased costs, the proposal emphasizes the importance of preventing the undesirable transfer of exhaust air between separate units, thereby protecting occupants' health and safety. The public hearing results supported the proposal, affirming the necessity of preventing backflow and contamination in multi-unit buildings.
IMC 501.6 Common ducts
The discharge from exhaust fans serving separate dwelling or sleeping units shall not be connected to a common duct or shaft, except where the common duct or shaft is maintained at a negative pressure.
Insight:
The proposed addition to the 2021 International Mechanical Code, section 501.6, seeks to address the issue of common exhaust ducts in buildings with separate dwelling or sleeping units. According to the proposal, exhaust fans serving these units should not be connected to a common duct or shaft unless it is maintained at a negative pressure. This is to prevent backflow, where the exhaust air from one unit could enter another unit if the fans are not running simultaneously. The current backdraft dampers in common exhaust systems have significant leakage rates, making it possible for odors, smoke, pathogens, and chemical irritants to transfer between units, which is highly undesirable. The ICC Plumbing/Mechanical/Gas Code Action Committee (PMG CAC), which aims to improve and enhance International Codes, submitted this proposal after several virtual meetings with interested parties who provided input on the issue.
The committee's reasoning for accepting the proposal is that positive pressure in exhaust ducts can cause airflow from one fan to leak through another non-operating fan, leading to potential contamination between units. To ensure safety and hygiene, maintaining a negative pressure in common exhaust shafts is crucial. This proposal will likely increase construction costs, particularly in scenarios where the cost of additional roof or wall penetrations is higher than combining ducts into a common system. Despite the potential for increased costs, the proposal emphasizes the importance of preventing the undesirable transfer of exhaust air between separate units, thereby protecting occupants' health and safety. The public hearing results supported the proposal, affirming the necessity of preventing backflow and contamination in multi-unit buildings.