BASC Search | Building America Solution Center

Install bottom layer of rigid insulation

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No insulation installed in cavity and not air sealed

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

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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.

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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.

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

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

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

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

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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

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Sufficient Cavity Space for Flex Ducts

Guide

Guide describing how and where to install ducts, to ensure enough cavity space to avoid compression of the flex ducts or duct insulation.

HVAC Ducts Shall Not Be Run within Exterior Walls

Guide

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

No Excessive Coiled or Looped Flex Ducts

Guide

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

HVAC duct layout

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Example of an HVAC installer’s balancing report form

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No Kinks or Sharp Bends in Flex Duct Installation

Guide

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

No Ducts or Air Handlers Located in Garage

Guide

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 attic, basement, or crawl space.

Design Options for Locating Ducts within Conditioned Space

Presentation

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.

Buried and Encapsulated Ducts, Jacksonville Florida

Reference

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