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Common Exhaust Duct Not Shared by Fans in Separate Dwellings

Scope

Common exhaust duct not shared by fans in separate dwellings
Common exhaust duct not shared by fans in separate dwellings

Install separate ducts for exhaust fans for each dwelling unit in multifamily buildings.

  • Install separate exhaust ducts for separate units.

If fans from separate dwellings do share a common exhaust duct, one of the following must apply:

  • The fans must run continuously, OR
  • Each outlet must have a back-draft damper to prevent cross-contamination when the fan is not running.

See the Compliance Tab for links to related codes and standards and voluntary federal energy-efficiency program requirements.

Description

Exhaust fans should always be ducted to a location outside the home (See Kitchen Exhaust Fans and Bathroom Exhaust Fans). Ideally, each exhaust fan should have its own individual duct to the outside and each unit should have its own ducting to prevent cross contamination. However, in multi-unit dwellings, such as condominiums or townhouses, builders sometimes prefer to connect the exhaust fans to a common exhaust duct, for reasons of layout or a wish to minimize penetrations through the roof (See Back-Draft Dampers at Shared Common Exhaust Duct). ENERGY STAR permits multiple units to share a common exhaust duct if each fan has a back-draft damper to prevent cross-contamination when the fan is not running or if all fans connected to the common exhaust duct are set to run continuously.

Exhaust fans in separate dwelling units should not share a common exhaust.
Figure 1. Exhaust fans in separate dwelling units should not share a common exhaust.

 

How to Install Back-Draft Dampers in Exhaust Fans to Make a Shared Duct Possible

  1. Install back-draft dampers where the exhaust duct meets the exhaust fan in each unit. The dampers should open when the fan is actively exhausting and should shut when the fan is off. When the exhaust fan is operating, the back-draft damper is pushed open by airflow to allow air to exit through the exhaust duct.

    Exhaust fans in separate dwelling units can share a common exhaust if each exhaust fan is equipped with a back-draft damper to prevent cross contamination.
    Figure 2. Exhaust fans in separate dwelling units can share a common exhaust if each exhaust fan is equipped with a back-draft damper to prevent cross contamination.

  2. Remember to remove any packing tape used to hold the dampers closed during shipping.

    The back-draft damper is open when the fan is actively exhausting and closes when the fan is off.
    Figure 3. The back-draft damper is open when the fan is actively exhausting and closes when the fan is off.

 

Ensuring Success

In multi-unit dwellings, such as condominiums or townhouses, the HERS rater will inspect the ventilation system exhaust ducts to ensure that one of the following is true: 1) each unit has its own exhaust duct that is individually ducted to the outside, or 2) if the units share a common exhaust duct, all of the fans are set to run continuously, or 3) each fan outlet has a back-draft damper to prevent cross-contamination when the fan is not running.

Region

No climate specific information applies.

Training

Right and Wrong Images

Fan shares exhaust and does not have dack-draft damper installed
Fan shares exhaust and does not have dack-draft damper installed
Fan shares exhaust and does not have dack-draft damper installed
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Source
Courtesy Of
EPA
Fan shares exhaust and has a back-draft damper installed
Fan shares exhaust and has a back-draft damper installed
Fan shares exhaust and has a back-draft damper installed
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Source
Courtesy Of
EPA
Back-draft damper still has a piece of tape that prevented it from rattling during shipping
Back-draft damper still has a piece of tape that prevented it from rattling during shipping
Back-draft damper still has a piece of tape that prevented it from rattling during shipping
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Source
Courtesy Of
EPA
Packing tape has been removed and damper will be able to function properly once fan is installed
Packing tape has been removed and damper will be able to function properly once fan is installed
Packing tape has been removed and damper will be able to function properly once fan is installed
View Image Download
Source
Courtesy Of
EPA
Fans from seperate dwellings exhausted together without back-draft dampers and not sealed
Fans from seperate dwellings exhausted together without back-draft dampers and not sealed
Fans from seperate dwellings exhausted together without back-draft dampers and not sealed
View Image Download
Source
Courtesy Of
EPA
Seperate dwellings with their own seperate exhaust terminations
Seperate dwellings with their own seperate exhaust terminations
Seperate dwellings with their own seperate exhaust terminations
View Image Download

Compliance

International Residential Code (IRC)

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Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Calcs-Plus

Pacific Northwest National Laboratory 

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This content is a work created with funding provided by the United States Department of Energy under Contract no DE-AC05-076RL01830 for the operation of Pacific Northwest National Laboratory. The information and guidance provided by Pacific Northwest National Laboratory (PNNL) in the content are intended solely for educational purposes only and do not constitute formal training or certification. It is provided with the explicit understanding that neither the United States Government nor the United States Department of Energy, nor the Contractor, nor any or their employees, nor any jurisdiction or organization that has cooperated in the development of these materials, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, software, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Viewers assumes full responsibility for all actions that they may take from information provided in this content including ensuring the safety, code compliance, and proper functionality of any products they choose to install. Installation and use of such products should be performed in accordance with local regulations and manufacturer instructions.