Air Sealing Bathroom and Kitchen Exhaust Fans

    Scope Images
    Image
    Air seal around kitchen and bathroom exhaust fans to keep conditioned air from leaking into unconditioned space.
    Scope

    Air seal around kitchen and bathroom exhaust fans to keep conditioned air from leaking into unconditioned space.

    • Using a saw, cleanly cut all a hole in the ceiling drywall no more than 1 inch larger in diameter than the fan box.
    • Seal holes in the fan housing with caulk, sealing putty, or metal tape.
    • Install the fan then seal around the fan with caulk or canned spray foam.
    • Seal the exhaust duct to the fan box with approved metal tape or mastic.
    • Seal around the exterior fan duct vent with caulk or a pre-made exterior wall gasket. 
    • If duct vents through the roof, install flashing around the vent that is properly integrated with roof paper and roofing material.
    • Do not vent exhaust fans into the attic.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

    Description

    Exhaust fans are typically installed in bathroom ceilings and in kitchen range hoods, or sometimes kitchen ceilings or walls, to provide spot ventilation. Generous holes are often cut in the ceiling drywall for installation of bath exhaust fans and kitchen exhaust fan ducts, leaving gaps where the fan box or duct is installed. While these gaps may be covered by decorative trim in the case of the exhaust fan box or be hidden in cabinets in the case of range hood exhaust fan ducts, those coverings will not stop air leaks. When the drywall is not sealed to the edges of the exhaust fan box or ducting, a considerable amount of conditioned air can leak through these gaps and into unconditioned attic space. The boxes themselves can also be leaky. Pressure and temperature differences between conditioned and unconditioned spaces encourage this air flow. These air leaks represent energy losses; they could also potentially allow warm, moisture-laden air into unconditioned attics where it can condense on cold surfaces, creating moisture problems. Air barriers need to be continuous to be effective; this means sealing all penetrations in exterior walls, ceilings, and floors adjoining unconditioned spaces.

    Be sure to schedule sealing around exhaust fans and ducts after fans and drywall have been installed. Responsibility for sealing air leaks around exhaust fans and ducts should be included in the contract for the appropriate trade, depending on the workflow at a specific job site.

    The gap around this kitchen exhaust duct represents a significant source of air leakage to the unconditioned attic.
    Figure 1. The gap around this kitchen exhaust duct represents a significant source of air leakage to the unconditioned attic (Source: Courtesy of PNNL). 

     

    How to Air Seal Holes around the Kitchen Exhaust Duct

    1. Cut openings for the duct that are no bigger than needed to fit the exhaust duct through the ceiling or top of the kitchen cabinet. Make clean, even cuts.
    2. After the exhaust duct is installed, air seal with caulk between the duct and drywall from the room side. If gaps are larger than a ¼ inch, use canned spray foam that is carefully applied. Do not use pieces of fibrous insulation; this insulation does not air seal. If gaps are larger than one inch, they can be sealed from the attic side with air-blocking material such as rigid foam that is cut to fit and sealed in place with caulk or spray foam. 
    3. Use caulk or pre-made exterior wall gaskets to air seal the exterior fan duct vent to the exterior wall. Ensure that exterior gaskets are properly integrated with the housewrap.
    Caulk or foam seal between the exhaust fan housing and the ceiling gypsum; install a gasket or caulk around the exterior exhaust duct vent.
    Figure 2. How to air seal around the kitchen exhaust (Source: Courtesy of PNNL). 

     

    How to Air Seal the Bathroom Fan Housing

    1. Cut openings in the ceiling that are no bigger than needed to fit the fan box. Make clean, even cuts in the drywall.
    2. After the fan is installed, air seal with caulk between the fan housing and drywall from the room side before installing trim. 
    3. If gaps are larger than a ¼ inch, use canned spray foam carefully applied so that trim will fit over it.
    4. If gaps are larger than a half inch, they can be sealed from the attic side with air blocking material such as rigid foam that is cut to fit and sealed in place with caulk or spray foam.  Do not use pieces of fibrous insulation; this does not air seal. 
    5. Seal holes in the fan housing with caulk or metal tape.
    6. Use caulk or premade exterior wall gaskets to air seal the exterior fan duct vent to the exterior wall. Ensure that exterior gaskets are properly integrated with housewrap.

    How to Create an Insulation Shield for the Exhaust Fan

    The bathroom exhaust fan box may have air leaks and holes in the casing. You may want to cover the fan to stop air leaks and to allow you to install insulation over it.

    The exhaust fan housing may have holes that allow conditioned air to leak into the attic.
    Figure 3. Uninsulated bath exhaust fan (Source: Courtesy of PNNL). 

     

    1. Create a 5-sided box from a solid air barrier material such as rigid foam, gypsum board, or plywood. Tape the seams of the box with housewrap tape (not duct tape) or seal with mastic. Cut an access in the box for the exhaust duct.
    2. Seal the box to the ceiling gypsum board and seal around the exhaust duct with caulk or canned spray foam.
      Build an air-tight rigid box to cover the exhaust fan.
      Figure 4. Bath exhaust fan with rigid foam box (Source: Courtesy of PNNL). 
    3. Cover the box with attic insulation.
      Cover the box with insulation.
      Figure 5. Fully insulated bath exhaust fan (Source: Courtesy of PNNL). 
    Ensuring Success

    Holes cut in the ceiling or wall for bathroom exhaust fan boxes and kitchen exhaust fan ducts should be visually checked to ensure that the opening around the fan box or exhaust duct is sealed with caulk or canned spray foam. An experienced technician can also check for air leaks with a smoke pencil or by feeling with the back of the hand. Air barrier effectiveness is measured at the whole-house level. Blower door testing, which is conducted as part of the whole-house energy performance test, may help indicate whether holes for exhaust fans in exterior walls or ceilings have been successfully sealed.

    Climate

    No climate specific information applies.

    Right and Wrong Images
    Image
    Wrong – Roughly cut hole that is larger than the fan, making it difficult to seal
    Wrong – Roughly cut hole that is larger than the fan, making it difficult to seal
    Image
    Right – Cleanly cut and properly sized hole
    Right – Cleanly cut and properly sized hole
    Image
    Wrong – Roughly cut hole that is larger than the fan, making it difficult to seal
    Wrong – Roughly cut hole that is larger than the fan, making it difficult to seal
    Image
    Right – Fan with a cleanly cut and properly sized hole has been air sealed to drywall
    Right – Fan with a cleanly cut and properly sized hole has been air sealed to drywall
    Image
    Wrong – Kitchen exhaust has not been air sealed
    Wrong – Kitchen exhaust has not been air sealed
    Image
    Right – Kitchen exhaust penetration has been sealed with caulk
    Right – Kitchen exhaust penetration has been sealed with caulk
    Videos

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

     

    ENERGY STAR Certified Homes, Version 3/3.1 (Rev. 09)

    National Rater Field Checklist

    Thermal Enclosure System.
    4. Air Sealing (Unless otherwise noted below, “sealed” indicates the use of caulk, foam, or equivalent material). 
    4.1 Ducts, flues, shafts, plumbing, piping, wiring, exhaust fans, & other penetrations to unconditioned space sealed, with blocking / flashing as needed.  

    Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.

     

    2009 International Energy Conservation Code (IECC)

    Table 402.4.2 Air Barrier and insulation Inspection Component Criteria, Shafts, penetrations: Duct shafts, utility penetrations, and flue shafts opening to exterior or unconditioned spare are air sealed.

    2012, 2015, and 2018 IECC

    Table R402.4.1.1 Air Barrier and Insulation Installation, Shafts/penetrations: Duct shafts, utility penetrations, and flue shafts opening to exterior or unconditioned space are air sealed.

    2021 IECC

    Table R402.4.1.1 Air Barrier and Insulation Installation, Shafts/penetrations: Duct shafts, utility penetrations, and flue shafts opening to exterior or unconditioned space are air sealed. Insulation shall be fitted tightly around shafts and penetrations, maintaining the required R-value.

    Retrofit:  2009, 2012, 2015, 2018,  and 2021 IECC

    Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

    Chapter 5 (in 2015, 2018, 2021). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.

    Existing Homes

    SCOPE

    In existing homes, air seal and insulate around new or existing bathroom and kitchen exhaust fans to minimize air leakage to and from unconditioned attics.  

    • Remove insulation around the exhaust fan on the attic side.
    • Inspect the attic floor around the fan box for air leaks. Inspect for air or water leakage around vent duct openings in the roof or exterior walls.
    • Repair or replace any damaged materials.
    • Fabricate and install an insulation shield as described in the Description Tab and air seal and/or insulate as needed.
    • See the Scope and Description tab for additional instructions.

    For more information on conditions that may be encountered when working in existing attics, see the Pre-Retrofit Assessment of Attics, Ceilings, and Roofs. Also see the U.S. Department of Energy’s Standard Work Specifications (SWS) guidance on air sealing ceiling penetrations.

    DESCRIPTION

    • Remove any existing insulation from around the exhaust fan on the attic side.
    • Inspect the attic floor around the fan box for air and water leaks. Inspect for air or water leakage around vent duct openings in the roof or exterior walls.
    • Repair or replace any damaged materials.
    • Fabricate and install an insulation shield as described in the Description Tab and air seal and/or insulate as needed.
    • See the Scope and Description tab for additional instructions.

    COMPLIANCE

    Alterations

    2009 IECC and 2009 IRC, 2012 IECC and 2012 IRC 

    2012 IECC, Section R101.4.3 / 2012 IRC N1101.3 and 2009 IECC 101.4.3 / 2009 IRC N1101.4.3 Alterations – General.  Alterations to an existing building or portion of a building should comply with the provisions of the code as they relate to new construction without requiring unaltered portion(s) of the existing building to comply with this code.

    2015 IECC and 2015 IRC, 2018 IECC and 2018 IRC

    2015 IECC/2015 IRC, Section R501.1.1/N1107.1.1 Existing Buildings – General.  Alterations to an existing building or portion of a building should comply with Sections R502/N1108, R503/N1109, or R504/N1110.  Unaltered portions of the existing building are not required to comply.

    R503.1/N1109.1 Alterations. General.  Alterations to any building or structure should comply with the requirements of the code for new construction.  Alterations should not negatively impact conformance of a building or structure to the provisions of this code; that is, code conformance should be the same as existed for the building or structure prior to the alteration.  Alterations should not create an unsafe or hazardous condition or overload existing building systems.  Alterations should be such that the altered building or structure uses no more energy than the existing building or structure prior to the alteration.

    See Compliance tab. 

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    U.S. Environmental Protection Agency
    Organization(s)
    EPA
    Publication Date
    Description
    Guide describing details that serve as a visual reference for each of the line items in the Thermal Enclosure System Rater Checklist.
    Author(s)
    Southface Energy Institute,
    ORNL
    Organization(s)
    DOE
    Publication Date
    Description
    Brochure with information for homeowners about the benefits of air sealing.
    Author(s)
    Baechler,
    Gilbride,
    Hefty,
    Cole,
    Love
    Organization(s)
    Pacific Northwest National Laboratory,
    Oak Ridge National Laboratory
    Publication Date
    Description
    Guide describing measures that builders in the cold and very cold climates can take to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

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

    Building Science Measures
    Building Science-to-Sales Translator

    High-Efficiency Fans = High-Efficiency Fans

    Image(s)
    Technical Description

    High-efficiency exhaust fans and ceiling fans are more energy efficient and quieter than standard fans.

    High-Efficiency Fans
    Sales Message

    High-efficiency fans minimize the wasted energy exhausting air while being virtually silent. What this means to you is odors and contaminants are efficiently removed without the noise. Isn’t it time homes used advanced technology components?

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