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Install bottom layer of rigid insulation

No insulation installed in cavity and not air sealed

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

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

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

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

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

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

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.

HVAC Ducts Shall Not Be Run within Exterior Walls

Guide describing the use of building cavities as supply or return ducts.

No Excessive Coiled or Looped Flex Ducts

Guide outlining how to correctly install flex ducts without excessive coils or loops.

HVAC duct layout

No Kinks or Sharp Bends in Flex Duct Installation

Guide outlining how to correctly install flex ducts without kinks or sharp bends.

No Ducts or Air Handlers Located in Garage

Guide describing how to design HVAC systems to be located within the conditioned space of the home, either in a utility closet or in an air sealed conditioned attic, basement, or crawl space.

Example of an HVAC installer’s balancing report form

Publication Date

Sun, 05/01/2011 - 12:00

Building Cavities Not Used as Supply or Return Ducts

Guide describing the use of building cavities as supply or return ducts.

Buried and Encapsulated Ducts, Jacksonville Florida

Author(s)

Consortium for Advanced Residential Buildings,

U.S. Department of Energy

Organization(s)

CARB,

DOE

Publication Date

November, 2013

Reference investigating the strategy of using buried and/or encapsulated ducts to reduce duct thermal losses in residential buildings.

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.