BASC Search | Building America Solution Center

Duct insulated with a minimum of R-8 insulation

Publication Date

Thu, 08/01/2013 - 12:00

Ducts are properly insulated and supported without compressing the insulation

Insulated floor above garage - cavity insulation with 1 inch rigid insulation with 2x2 wood furring

DWG

PDF

Ducts are insulated but strapping is compressing the insulation therefore reducing the R-value

Duct and HVAC Insulation

Author(s)

North American Insulation Manufacturers Association

Organization(s)

NAIMA

Publication Date

January, 2010

Information sheet with HVAC duct insulation, testing, maintenance and performance information.

Right – Batt insulation provides additional insulation for the home’s main duct chase.

Publication Date

Mon, 09/30/2019 - 12:00

Sealed and Insulated Flex Ducts

Publication Date

July, 2015

Video describing how to seal and insulate flex ducts.

Sealed and Insulated Metal Ducts

Guide describing how to air seal and insulate metal ducts.

Sealed and Insulated Flex Ducts

Guide describing how to air seal and insulate flex ducts.

Ducts Buried in Attic Insulation

Guide describing buried ducts in loose-fill attic insulation, a method that can only be used in dry climates.

Ducts Buried in Attic Insulation and Encapsulated

Guide describing approaches to burying and encapsulating ducts in unconditioned attics to increase the overall R-value of duct insulation.

Air seal and insulate flex ducts

Publication Date

Fri, 10/28/2011 - 12:00

Install bottom layer of rigid insulation

Duct insulation is installed over boot

Insulation does not cover boot and is not sealed

Duct is located in unconditioned space and is not insulated

Sealed and Insulated Fiber Board Ducts

Guide describing how to air seal and insulate fiber board ducts.

Prepare chase with adhesive for bottom insulation

Insulation does not cover boot and is not sealed

No insulation installed in cavity and not air sealed

Duct is located in unconditioned space and is properly insulated

Wrong: Insulation not fully enclosing duct chase

Reference

Measure Guideline: Summary of Interior Ducts in New Construction, Including an Efficient, Affordable Method to Install Fur-Down Interior Ducts

Author(s)

Beal David,

McIlvaine Janet E R,

Fonorow Ken,

Martin Eric

Organization(s)

Building America Partnership for Improved Residential Construction,

BA-PIRC,

National Renewable Energy Laboratory,

NREL,

Florida Solar Energy Center,

FSEC,

U.S. Department of Energy,

DOE

Document illustrating guidelines for efficient installation of interior duct systems in new housing.

Publication Date

Tue, 11/01/2011 - 12:00

The jump duct should be insulated and sealed at registers

Second layer of rigid insulation is adhered with foam

Ducts Encapsulated in Spray Foam and Buried in Attic Insulation

Publication Date

September, 2015

Video describing various ways to bring HVAC ducts installed in an attic within the thermal envelope of the home by insulating the attic or by covering the ducts with spray foam and burying them in fibrous insulation.

Measure Guideline: Sealing and Insulating Ducts in Existing Homes

Author(s)

Aldrich Robb,

Puttagunta Srikanth

Organization(s)

Consortium for Advanced Residential Buildings,

CARB,

National Renewable Energy Laboratory,

NREL,

Steven Winter Associates,

SWA

Publication Date

December, 2011

Report describing the sealing and insulating of HVAC duct systems in existing homes.

Wrong – Fibrous insulation does not air seal

Publication Date

Fri, 10/28/2011 - 12:00

Prescriptive Path: Supply ducts in unconditioned attic have insulation ≥ R-8. Performance Path: Supply ducts in unconditioned attic have insulation ≥ R-6

Pull the insulation and outer liner of the flex duct over the collar to come in full contact with the liner and insulation of the trunk line or fitting and tape in place

Boot has been covered with insulation and sealed with mastic

Publication Date

Fri, 10/28/2011 - 12:00

Inadequate amount of insulation installed with compression, misalignment, and voids

Spray foam insulation used for raised ceiling duct chase

Wrong – Insulation should not be pinched where flex ducts connect to the trunk duct as compression of the insulation here can lead to cold spots and condensation on the duct surface.

Publication Date

Fri, 12/31/2021 - 12:00

Seal bottom layer of rigid insulation with adhesive, tape and nails

Spray foam insulation used for raised ceiling duct chase.

The attic duct chase insulated and sealed to the attic floor with spray foam

Trunk to duct connections are properly insulated and have been sealed with mastic

Right: Ducts are completely buried beneath insulation to the depth specified in the plans

Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck

Guide describing a method for insulating an unvented attic by spraying foam insulation along the underside of the roof deck.

Wrong: Ducts are held above the ceiling plane with strapping to provide a good angle into top-entry boots. Once the ceiling insulation is added, this duct will protrude from the ceiling insulation and will not be buried

Wrong - Flex duct resting on floor compressing insulation and causing condensation

A second layer of rigid insulation is installed over the 2 in. by 4 in. retaining strip

Publication Date

Wed, 10/08/2014 - 12:00

Right – Plastic tenting increases the height of the insulation above ducts that are located in the attic.

Publication Date

Mon, 09/30/2019 - 12:00

Right- This flue pipe has been air sealed with sheet metal and fire-rated caulk and an insulation dam has been constructed to keep insulation from touching the hot flue pipe

Seal all joints and seams in the metal ductwork with mastic before installing insulation

Wrong - Duct insulation and vapor barrier do not cover all of the flex duct.

Publication Date

Fri, 12/07/2018 - 12:00

Cleaning Fibrous Glass Insulated Duct (Ductboard / Duct Board) Systems - Recommended Practices

Author(s)

North American Insulation Manufacturers Association

Organization(s)

NAIMA

Publication Date

June, 2019

Manual showing duct cleaning contractors how to identify the different types of insulated air ducts, how to open each type for access by cleaning equipment and personnel, how to close and seal openings after cleaning.

Right: Spray foam air seals and insulates raised ceiling duct chase

Wrong - Duct insulation and vapor barrier do not cover all of the flex duct.

Publication Date

Fri, 12/07/2018 - 12:00

Wrong - Flex duct insulation is overly compressed in 3 ways; Zip-tie fastener is over the insualtion not under the insulation at the duct boot collar, duct turning radius is too tight, and support strap is too tight.

Publication Date

Sat, 01/19/2019 - 12:00

Monitoring of Unvented Roofs with Fibrous Insulation, Diffusion Vents, and Interior Vapor Control in a Cold Climate

Author(s)

Ueno Kohta,

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

September, 2020

Report detailing a three-winter study on unvented roof assemblies in a cold climate, assessing insulation material, ridge diffusion vent presence, vapor control membranes, relative humidity, and interstitial airflow. Results indicate that utilizing air-permeable fibrous fill insulations in unvented...

Monitoring of Unvented Roofs with Fibrous Insulation, Diffusion Vents, and Interior Vapor Control in a Cold Climate

Author(s)

Ueno Kohta,

Lstiburek Joseph W

Organization(s)

Building Science Corporation,

BSC

Publication Date

September, 2020

Report detailing a three-winter study on unvented roof assemblies in a cold climate, assessing insulation material, ridge diffusion vent presence, vapor control membranes, relative humidity, and interstitial airflow; results indicate that utilizing air-permeable fibrous fill insulations in unvented...

Standard 2 in. by 4 in. stud secures duct chase - made of rigid insulation in this example

Right – Flex ducts are properly supported with straps that don’t pinch the insulation; closed-cell spray foam will be applied to the underside of the roof deck of this hot-humid climate home to provide an insulated attic space for the HVAC ducts.

Publication Date

Thu, 09/30/2021 - 12:00

Cavity used for return is not insulated and is not air sealed, which will pull in air from outside

Wrong- A tie strap should not be used over the duct outer liner because it can compress the insulation. Tuck in the fibrous insulation and seal the outer liner to the connecting duct with mastic or foil tape (Steven Winter Associates 2013).

All other supply ducts and all return ducts in unconditioned space have insulation ≥ R-6

Publication Date

Fri, 10/28/2011 - 12:00

Buried Ducts within Ceiling Insulation of Vented Attics in all Climate Zones - Code Compliance Brief

Publication Date

January, 2020

The intent of this brief is to provide code-related information about buried ducts in vented attics to help ensure that the measure will be accepted as being in compliance with the code. Providing notes for code officials on how to plan review and conduct field inspections can help provide jurisdictional officials with information for acceptance. Providing the same information to all builders, designers, and others is expected to result in increased compliance and fewer innovations being questioned at the time of plan review and/or field inspection.

A nylon draw band and tensioning tool are used to secure the inner coil of the pre-insulated flexible duct

Publication Date

Wed, 11/21/2012 - 12:00

A nylon draw band and tensioning tool are used to secure the inner liner of the pre-insulated flexible duct

Wrong: Ductwork is not fully encapsulated with ccSPF insulation. The duct jacket is still fully visible at sections of the duct

Buried ducts are laid on the floor of a vented attic then covered with spray foam and blown attic floor insulation

Publication Date

Wed, 09/01/2021 - 12:00

Right – All supply ducts in this home were located in conditioned space; any return ducts that were located in the attic were insulated with closed-cell spray foam and buried in the blown-in attic insulation to prevent air leakage and heat loss.

Publication Date

Thu, 09/30/2021 - 12:00

When wrapping metal ducts with insulation allow two inches of overlap and staple along the seam with outward clinching staples

If a dropped soffit is used to house a duct, the soffit space must equal the duct diameter plus the insulation thickness

If HVAC duct must be installed in an exterior wall, separate it from the exterior with at least R-6 of continuous rigid insulation

Right - the vapor barrier is extended up the sides of the piers in this crawlspace, which is sealed and insulated to house the HVAC ducts.

The sealed, insulated crawlspace is a clean, dry location to house the main floor heating ducts and also provides bonus storage space.

Right – Rigid foam is installed behind HVAC ducts to provide additional insulation to the ducts which are installed within the conditioned space.

Publication Date

Mon, 09/30/2019 - 12:00

Wrong: open wall cavity connected to this return air plenum is allowing cellulose attic insulation to be pulled into the furnace

Publication Date

Sun, 06/01/2014 - 12:00

The attic is sealed and insulated along the underside of the roof deck with 5.5 inches of polyurethane spray foam, providing conditioned space for the HVAC system.

A ducted central return brings air from central return registers back to the air handler through insulated, air-sealed ducts

Publication Date

Thu, 03/09/2017 - 12:00

R-6 flexible duct has 2 inches of insulation around the inner liner so a 12-inch duct requires a 16x16-inch chase

Because this ICF and spray foamed house is so well insulated, the HVAC system is smaller, the round metal ducts are smaller diameter, and the duct layout is more compact.

Publication Date

Wed, 01/01/2014 - 12:00

HVAC ducts can be encapsulated in 3 inches of closed-cell spray foam, then buried in R-49 of blown fiberglass insulation after the ceiling drywall is installed in the vented attic.

Wrong – Don’t use nails to fasten poly vapor barrier around flex ducts; it will allow moist air to reach the ducts where it could condense and ruin the insulation.

Publication Date

Tue, 04/13/2021 - 12:00

To attach the flex duct to a main trunk duct or any other connection, the flex duct is pulled over the connecting collar at least 2 inches past the raised bead, then the insulation is pulled back

The main trunk line of the ducts runs within an insulated duct chase installed in a notch designed into the roof trusses that runs the length of the home to provide supply air directly to most of the home’s ceiling registers.

Wrong – These flex ducts are pulled taut, which is correct but they are inadequately supported with straps that are spaced too far apart and are too tight causing pinching of the insulation and turns are sharp rather than gradual.

A floor cavity between the first and second floor can provide a conditioned space for HVAC ducts if the rim joists are insulated and air sealed, if sufficient space is available, and if open-web floor joists are used

Publication Date

Wed, 01/01/2014 - 12:00

Specially designed roof trusses come with a two-foot by two-foot notch cut next to the center post providing space to install an insulated duct chase inside the home’s conditioned space but above the normal ceiling height.

This Habitat for Humanity builder ordered roof trusses with a 2-foot by 2-foot notch next to the center post then lined the cutout with rigid foam to form an insulated central duct chase to bring the heating and cooling ducts within the conditioned space.

HVAC ducts, cavities used as ducts, and combustion inlets and outlets may pass perpendicularly through exterior walls but shall not be run within exterior walls unless at least R-6 continuous insulation is provided on exterior side of the cavity

Right - The precast insulated concrete walls of the basement provide a conditioned space for the high-efficiency (18 SEER, 9.5 HSPF) air-source heat pump, with its variable-speed fan, five-stage compressor, and MERV 11 filter.

Controlling Moisture in Unvented Attics - Code Compliance Brief

Publication Date

May, 2017

The intent of this brief is to provide code-related information about controlling moisture in unvented attics by installing a vapor diffusion port/vent that would convey water vapor from an unvented attic to the outside when air-permeable insulation materials are installed and can be verified as being in compliance with the related codes and standards for residential construction. Providing consistent information to document compliance with codes and standards to all relevant parties responsible for verifying compliance (e.g., code officials, builders, contractors, designers, etc.) is expected to result in increased compliance and more timely, less challenging and more uniform plan review and field inspections.

Encapsulated Ducts

Publication Date

July, 2015

Video describing air sealing and insulation for encapsulated ducts.

Ducts in Raised Ceiling Sections

Guide describing method for designing and installing ducts in a raised ceiling chase.

Compact Buried Ducts in a Hot-Humid Climate House

Author(s)

Mallay David

Organization(s)

Home Innovation Research Labs,

HIRL

Publication Date

January, 2016

Report on heating and cooling air-distribution ducts that are insulated, installed close to the ceiling in a vented attic and covered with attic insulation to minimize energy loss.

Building America Top Innovations 2013: Buried and Encapsulated Ducts

Author(s)

Pacific Northwest National Laboratory,

Steven Winter Associates

Organization(s)

PNNL,

CARB,

SWA

Publication Date

September, 2013

Case study describing a DOE Building America Top Innovation on HVAC ducts located in vented attics that are encapsulated in foam and buried in attic insulation.

Encapsulated Ducts

Guide that illustrates how and when to encapsulate ductwork in unconditioned attics, increases the R-value of duct insulation, mitigating condensation issues and reducing air leakage.

Support at Intervals for Flex Ducts

Guide describing how to hang ducts with supporting straps or saddles to adequately support ducts so they do not sag and are not pinched or compressed in a manner that would cause damage to the ducts, the duct insulation, or the duct air barrier covering.

Sufficient Cavity Space for Flex Ducts

This measure guide describes how to correctly install ducts, ensuring enough cavity space to avoid compression.

Sealed Attics?

Author(s)

Coble Brian

Organization(s)

Home Energy Magazine

Publication Date

January, 2010

Article describing how insulating and air sealing unfinished attic spaces can lead to reduced energy bills in some homes.

Builders Challenge High Performance Builder Spotlight: David Weekley Homes, Houston, Texas

Author(s)

Pacific Northwest National Laboratory

Organization(s)

PNNL

Publication Date

December, 2009

Case study describing new home construction in the hot-humid climate, optimizing thermal enclosure, HVAC, water heating and lighting measures.