Encapsulated Ducts

Scope

Ducts located in unconditioned attics are encapsulated with closed-cell spray polyurethane foam (ccSPF), which increases the R-value of the duct insulation, mitigates condensation issues, and reduces air leakage. This solution is only recommended for retrofits where burying the ductwork beneath loose-fill insulation is impractical. It can also be utilized for a portion of the duct system that is impractical to bury. In new construction, buried & encapsulated ducts involve a negligible increase in cost over encapsulation alone. The figure to the right provides a picture of an encapsulated duct installation. Encapsulated ducts can be installed in all climate zones, including moist and marine climate zones.

  1. Install ductwork
  2. Mastic-seal all duct connections.
  3. Test total duct leakage.
  4. Apply at ccSPF to all ducts.

For further information, see Ducts Buried in Attic Insulation and Ducts Buried in Attic Insulation & Encapsulated.

Description

Encapsulated ducts increase the R-value of the ductwork and reduce air leakage. The effective R-value of an encapsulated duct installation depends on the size of the ducts, the insulation value of the duct insulation, and the thickness of the ccSPF insulation. The effective R-value of 8-in round ducts encapsulated with 1.5 in of ccSPF is 12.7.

How to Install Encapsulated Ducts

1.    Install ductwork with a minimum of R-8 duct insulation in accordance with low-profile duct design.

This duct is insulated with a minimum of R-8 insulation

This duct is insulated with a minimum of R-8 insulation. Reference

2.    Mastic-seal all connections and pull insulation jackets fully over joints and connections following best-practice duct sealing strategies. Tool-tightened tension ties must be applied to the inner and outer liners.

Connection mastic-sealed  Connection mastic-sealed  Connection mastic-sealed

This connection was mastic-sealed and insulation jackets were fully pulled over joints and connections following best-practice duct sealing strategies. Tool-tightened tension ties were applied to the inner and outer liners. Reference

3.    Test total duct leakage to assure performance levels are met (total duct leakage < 3 cfm25 per 100 ft2 of conditioned space). Testing should be performed before encapsulation because it may be difficult to correct sealing issues after the application of spray foam.

Total duct leakage testing

Total duct leakage was tested to assure performance levels are met (total duct leakage < 3 cfm25 per 100 ft2 of conditioned space). Testing was performed before encapsulation because it is difficult to correct sealing issues after the application of spray foam. Reference

4.    Apply at least 1.5 in of ccSPF to all duct surfaces, including trunks, branches, and register boots. Where obstructions make the bottom of ducts inaccessible (such as when a wide trunk is placed on top of and perpendicular to the ceiling framing), ducts may be placed on 1.5 in thick XPS or polyisocyanurate insulation board.

Ensuring Success

To minimize air leaks and maximize effective R-values, ccSPF must be applied to all surfaces to the ductwork or the ducts must be sealed to the ceiling gypsum board with ccSPF. All duct connections should be mastic sealed and ducts should be tested for leakage with a duct blaster before the ccSPF is applied.

Special attention is needed to ensure code compliance for buried & encapsulated ducts because they include spray foam insulation applied to ductwork. The 2009 IRC allows exposed installations of ccSPF in attics, but the spray foam must be specifically approved for installation without an ignition barrier. If the spray foam used is not specifically approved for exposed attic installations, encapsulated ducts may not be installed using the spray foam.

Climate

Encapsulated ducts may be installed in all climate zones, including moist (A) and marine (C) climate zones.

 

IECC climate zone map

IECC Climate Zone Map

Training

Right and Wrong Images

Presentations

  1. Design Options for Locating Ducts within Conditioned Space
    Author(s): Zoeller
    Organization(s): Steven Winter Associates

    Presentation with technical training covering several possible approaches to locating ducts within the home’s air and thermal barriers, and then dig into design considerations and details for the spray foam encapsulation approach.

Videos

  1. Encapsulated Ducts
    Publication Date: July, 2015

    Video describing air sealing and insulation for encapsulated ducts.

CAD Images

None Available

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 (Rev 08)
Buried & encapsulated ducts have the same requirements as all other ductwork installed in unconditioned attics.

Rater Field Checklist, 6. Duct Quality Installation

6.3 All supply and return ducts in unconditioned space, including connections to trunk ducks, are insulated to ≥ R-6.

6.4 Rater-measured total duct leakage meets one of the following two options: 

6.4.1 Rough-in:  The greater of ≤ 4 CFM25 per 100 sq. ft. of conditioned floor area (CFA) or ≤ 40 CFM, with the air handler and all ducts, building cavities used as ducts, and duct boots installed. In addition, all duct boots are sealed to the finished surface; rater-verified at final.

6.42 Final:  The greater of ≤ 8 CFM25 per 100 sq. ft. of CFA or ≤ 80 CFM, with the air handler and all ducts, building cavities used as ducts, duct boots, and register grilles atop the finished surface (e.g., drywall, flooring) installed.

6.5 Rater-measured duct leakage to the outdoors is ≤ 4 CFM25 per 100 sq. ft. of CFA or ≤ 40 CFM25.

DOE Zero Energy Ready Home
Encapsulated ducts are not compliant with the DOE Zero Energy Ready Home. Buried & encapsulated ducts may be compliant.

2009 IECC  /  2009 IRC

IECC R403.2/IRC N1103.2 Ducts.

IECC R403.2.1/IRC N1103.2.1 Insulation (Prescriptive). Supply ducts in attics shall be insulated to a minimum of R-8. All other ducts shall be insulated to a minimum of R-6.

               Exception:  Ducts or portions thereof located completely inside the building thermal envelope.

IECC R403.2.2/IRC N1103.2.2 Sealing (Mandatory).  All ducts, air handlers, filter boxes, and building cavities used as ducts shall be sealed.  Joints and seams shall comply with Section M1601.4 of the International Residential Code. [Exceptions may apply.]

               Duct tightness shall be verified by either of the following:

  1. Post-construction test:  leakage to outdoors shall be less than or equal to 8 cfm (226.5 L/min) per 100 ft2 (9.29 m2) of conditioned floor area or a total leakage less than or equal to 12 cfm (339.8 L/min) per 100 ft2 of conditioned floor area when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the entire system, including the manufacturer’s air handler enclosure. All register boots shall be taped or otherwise sealed during the test.
  2. Rough-in test:  Total leakage shall be less than or equal to 6 cfm (169.9 L/min) per 100 ft2 of conditioned floor area when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the roughed in system, including the manufacturer’s air handler enclosure. All register boots shall be taped or otherwise sealed during the test. If the air handler is not installed at the time of the test, total leakage shall be less than or equal to 4 cfm (113.3 L/min) per 100 ft2 of conditioned floor area.

    Exceptions: Duct tightness test is not required if the air handler and all ducts are located within conditioned space.

IECC R403.2.3/IRC N1103.2.3 Building cavities (Mandatory).  Building framing cavities shall not be used as supply ducts.

 

2012 IECC  / 2012 IRC

IECC R403.2/IRC N1103.2 Ducts.  Ducts and air handlers shall be in accordance with IECC R403.2.1 through R403.2.3 (IRC N1103.2.1-N1103.2.3).

IECC R403.2.1/IRC N1103.2.1 Insulation (Prescriptive).  Same as 2009 IECC/IRC.

IECC R403.2.2/IRC N1103.2.1 Sealing (Mandatory).  Ducts, air handlers, and filter boxes shall be sealed.  Joints and seams shall comply with either the International Mechanical Code or International Residential Code, as applicable [Exceptions may apply.]

Exceptions:

1. Air-impermeable spray foam products shall be permitted to be applied without additional joint seals.

2. Where a duct connection is made that is partially inaccessible, three screws or rivets shall be equally spaced on the exposed portion of the joint so as to prevent a hinge effect.

3. Continuously welded and locking-type longitudinal joints and seams in ducts operating at static pressures less than 2 inches of water column (500 PA) pressure classification shall not require additional closure systems.

Duct tightness shall be verified by either of the following:

  1. Post-construction test: Total leakage shall be less than or equal to 4 cfm (113.3 L/min) per 100 ft2 (9.29 m2) of conditioned floor area when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the entire system, including the manufacturer’s air handler enclosure. All register boots shall be taped or otherwise sealed during the test.
  2. Rough-in test.  Total leakage shall be less than or equal to 4 cfm per (113.3 L/min) per 100 ft2 (9.29 m2) of conditioned floor area when tested at a pressure differential of 0.1 inches w.g. (25 Pa) across the system, including the manufacturer’s air handler enclosure. All registers shall be taped or otherwise sealed during the test. If the air handler is not installed at the time of the test, total leakage shall be less than or equal to 3 cfm (85 L/min) per 100 ft2 of conditioned floor area.

    Exception: The total leakage test is not required for ducts and air handlers located entirely within the building thermal envelope.

IECC R403.2.2.1/IRC N1103.2.2.1 Sealed air handler.  Air handler shall have a manufacturer’s designation for an air leakage of no more than 2 percent of the design air flow rate when tested in accordance with ASHRAE 193.

IECC R403.2.3/IRC N1103.2.3 Building cavities (Mandatory).  Building framing cavities shall not be used as ducts or plenums.

 

2015 IECC and 2018 IECC  /  2015 IRC and 2018 IRC

IECC R403.2/IRC N1103.3 Ducts.  Ducts and air handlers shall be in accordance with Sections R403.3.1 through R403.3.5 (IRC N1103.3.1-N1103.3.5).

IECC R403.3.1/IRC N1103.3.1 Insulation (Prescriptive).  Supply and return ducts in attics shall be insulated to a minimum of R-8 where 3 inches (76 millimeters) in diameter and greater and R-6 where less than 3 inches (76 millimeters) in diameter.  Supply and return ducts in other portions of the building shall be insulated to a minimum of R-6 where 3 inches (76 millimeters) in diameter or greater and R-4.2 where less than 3 inches (76 millimeters) in diameter. 

Exception:  Ducts or portions thereof located completely inside the building thermal envelope

IECC R403.3.2/IRC N1103.3.2 Sealing (Mandatory).  Ducts, air handlers, and filter boxes shall be sealed.  Joints and seams shall comply with either the International Mechanical Code or International Residential Code, as applicable.

Exceptions [In 2015 IECC/IRC only; these exceptions were not included in the 2018 IECC/IRC.)

  1. Air-impermeable spray foam products shall be permitted to be applied without additional joint seals.
  2. For ducts having a static pressure classification of less than 2 inches of water column (500 Pa), additional closure systems shall not be required for continuously welded joints and seams, and locking-type joints and seams of other than the snap-lock and button-lock types.

IECC R403.3.2.1/IRC N1103.3.2.1 Sealed Air Handler.  Air handlers shall have a manufacturer’s designation for an air leakage of no more than 2% of the design air flow rate when tested in accordance with ASHRAE 193.

IECC R403.3.3/IRC N1103.3.3 Duct testing (mandatory).  Ducts shall be pressure tested to determine air leakage by one of the following methods:

  1. Rough-in test.  Total leakage shall be measured with a pressure differential of
    0.1 inch water gage (25 Pa) across the system, including the manufacturer’s air handler enclosure if installed at the time of the test.  All registers shall be taped or otherwise sealed during the test.
  2. Post-construction test.  Total leakage shall be measured with a pressure differential of 0.1 inch water gage (25 Pa) across the entire system, including the manufacturer’s air handler enclosure.  Registers shall be taped or otherwise sealed during the test.

Exception:

A duct air leakage test shall not be required where the ducts and air handlers are located entirely within the building thermal envelope

 [New Exception added to 2018 IECC/IRC] A duct air leakage test shall not be required for ducts serving heat or energy recovery ventilators that are not integrated with ducts serving heating or cooling systems.

A written report of the results of the test shall be signed by the party conducting the test and provided to the code official.  [Because the ducts will be installed outside the building thermal envelope, this exception would not apply.]

IECC R403.3.4/IRC N1103.3.4 Duct leakage (Prescriptive).

The total leakage of the ducts, where measured in accordance with Section R403.3.3, shall be as follows:

  1. Rough-in test.  The total leakage shall be less than or equal to 4 cfm per (113.3 L/min) per 100 ft2 (9.29 m2) of conditioned floor area where the air handler is installed at the time of the test. Where the air handler is not installed at the time of the test, the total leakage shall be less than or equal to 3 cfm (85 L/min) per 100 ft2 of conditioned floor area.
  2. Post-construction test: Total leakage shall be less than or equal to 4 cfm (113.3 L/min) per 100 ft2 (9.29 m2) of conditioned floor area.

IECC R403.3.5/IRC N1103.3.5 Building cavities (Mandatory). Building framing cavities shall not be used as ducts or plenums.

 

2009 IRC  /  2012 IRC  /  2015 IRC2018 IRC

Ducts are designed, constructed, and installed in accordance with the provisions of IRC M1601 and  M1602,  ACCA Manual D, and manufacturers’  guidance.    

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.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL, CARB, Steven Winter Associates
    Publication Date: September, 2013

    Case study on a DOE Building America 2013 top innovation describing research by the Consortium for Advanced Residential Buildings (CARB), a Building America research team led by Steven Winter Associates, on HVAC ducts located in vented attics that are encapsulated in foam and buried in attic insulation.

  2. Author(s): CARB
    Organization(s): CARB
    Publication Date: November, 2013

    Case study exploring how using buried and/or encapsulated ducts can reduce duct thermal losses in existing homes.

References and Resources*

  1. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2009

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  2. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2012

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  3. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2017

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  4. Author(s): EPA
    Organization(s): EPA
    Publication Date: June, 2013
    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).
  5. Author(s): Shapiro, Zoeller, Mantha
    Organization(s): CARB
    Publication Date: August, 2013
    Document covering the technical aspects of buried and insulated ducts (BEDs), as well as the advantages, disadvantages, and risks of BEDs compared to alternative strategies.
  6. Author(s): Shapiro, Magee, Zoeller
    Organization(s): CARB
    Publication Date: February, 2013
    Report including an overview of the buried duct research and information the retrofit methodology used to install and test the three existing duct systems, including short- and long-term data collection.

Contributors to this Guide

None Available

Last Updated: 11/09/2017

Mobile Field Kit

The Building America Field Kit allows you to save items to your profile for review or use on-site.