BASC Search | Building America Solution Center

Boot has been covered with insulation and sealed with mastic

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

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Spray foam insulation used for raised ceiling duct chase

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

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Spray foam insulation used for raised ceiling duct chase.

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

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

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

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The duct for this exhaust fan is properly routed through the roof and the duct is insulated

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Insulation for rigid ducts comes in large rolls like this 4-ft x 50-ft roll consisting of a Foil-Scrim-Kraft (FSK) vapor barrier attached to the fiberglass insulation.

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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

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

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Rigid foam was used to insulate this return plenum attached to this flex duct.

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This exhaust fan duct is properly insulated and is properly vented through the roof

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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

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

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

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

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

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Form an insulation dam of heat-resistant insulation with at least 3 inches of clearance around a flue pipe in the attic after air sealing around the pipe with sheet metal and fire-rated caulk or canned foam

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

Reference

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

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A box was constructed of rigid foam and sheathing tape to insulate this return plenum in the attic.

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

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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.

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

Reference

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

Reference

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...

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

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