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The grille in the photo on the left brings air into a return air plenum under an air handler platform. As shown in the infrared image on the right, the plenum is not air sealed so hot attic air is being pulled into the air handler closet.

The grille in the photo on the left brings air into a return air plenum under an air handler platform. As shown in the infrared image on the right, the plenum is not air sealed so hot attic air is being pulled into the air handler closet.

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Seams and connections in rigid metal ducts are air sealed using tape or mastic.

Seams and connections in rigid metal ducts are air sealed using tape or mastic.

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Building America Energy Performance Brief: Air Sealing Duct Boots and Duct Chases

Case Study

Case study describing how to inspect and air seal around duct boots and chases in order to limit air leakage in a home.

Air seal all holes and seams in the furnace cabinet with mastic, foil tape, or putty

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Fiberglass mesh tape is installed around a duct boot in preparation for air sealing with mastic

Fiberglass mesh tape is installed around a duct boot in preparation for air sealing with mastic

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Duct boot is air sealed to ceiling by covering the seam with fiberglass mesh tape and mastic

Duct boot is air sealed to ceiling by covering the seam with fiberglass mesh tape and mastic

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Duct System Flammability and Air Sealing Fire Separation Assemblies in the International Residential Code

Reference

Report identifying two barriers that limit the ability of builders to explore opportunities for higher levels of energy efficiency in housing: the use of duct system materials that inherently achieve airtightness and are right-sized for low-load houses, and, the ability to air seal fire separation...

Right – Chase capped with rigid air barrier and duct work penetrations properly sealed

Right – Chase capped with rigid air barrier and duct work penetrations properly sealed

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Air seal duct boot to ceiling by installing fiberglass mesh tape and mastic over seam

Air seal duct boot to ceiling by installing fiberglass mesh tape and mastic over seam

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Spray foam air seals gaps around holes and drywall-to-top plate seams.

Spray foam air seals gaps around holes and drywall-to-top plate seams.

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Fiberglass mesh tape is installed around a duct boot in preparation for air-sealing the seams with mastic.

Fiberglass mesh tape is installed around a duct boot in preparation for air-sealing the seams with mastic.

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Wrong: The return plenum is not air sealed to separate it from the wall cavities and it should not be used for storage

Wrong: The return plenum is not air sealed to separate it from the wall cavities and it should not be used for storage

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Air seal around all duct shafts and flues installed through ceilings, walls, or flooring to keep conditioned air from leaking into unconditioned space.

Air seal around all duct shafts and flues installed through ceilings, walls, or flooring to keep conditioned air from leaking into unconditioned space.

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Wrong: Open wall cavities in the un-air-sealed return plenum connect the plenum to attic spaces

Wrong: Open wall cavities in the un-air-sealed return plenum connect the plenum to attic spaces

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The gap between the duct boot and the drywall is air sealed by covering the seam with fiberglass mesh tape and mastic.

The gap between the duct boot and the drywall is air sealed by covering the seam with fiberglass mesh tape and mastic.

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Plan view of duct or pipe penetration through exterior wall showing flashing and air sealing details

Plan view of duct or pipe penetration through exterior wall showing flashing and air sealing details

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Right – A contractor installs mastic in branch duct take offs to air seal the seams where they attach to the trunk duct.

Right – A contractor installs mastic in branch duct take offs to air seal the seams where they attach to the trunk duct.

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The seam between this duct register and the wood flooring is sealed with caulk to prevent air leakage into the house from the crawlspace below.

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Right – The termination of this kitchen exhaust duct is sealed to the wall to keep out air and water and is screened to keep out pests.

Right – The termination of this kitchen exhaust duct is sealed to the wall to keep out air and water and is screened to keep out pests.

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The large hole that was cut in the subfloor penetration for this HVAC duct has been air-sealed using sheet metal, mastic, and metal tape.

The large hole that was cut in the subfloor penetration for this HVAC duct has been air-sealed using sheet metal, mastic, and metal tape.

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HVAC equipment should never be exposed to the garage; instead, locate them in air-sealed closets, with weatherstripping, spring-loaded hinges, and mastic.

HVAC equipment should never be exposed to the garage; instead, locate them in air-sealed closets, with weatherstripping, spring-loaded hinges, and mastic.

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Wrong - This is a poorly sealed chase with no solid air barriers along the sides of the chase and no caulk around the electrical wires installed through the ceiling of the chase.

Wrong - This is a poorly sealed chase with no solid air barriers along the sides of the chase and no caulk around the electrical wires installed through the ceiling of the chase.

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The hole in the air handler box, on left, was covered with a piece of 30-gauge sheet metal that was cut to size and sealed in place with screws and mastic.

The hole in the air handler box, on left, was covered with a piece of 30-gauge sheet metal that was cut to size and sealed in place with screws and mastic.

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The fiberglass insulation stuffed into the large hole around this HVAC duct will not prevent air leakage from the unconditioned basement to the conditioned space above; the large gap should be sealed with a rigid air barrier and caulked or spray foamed.

Fiberglass insulation stuffed into the large hole around this HVAC duct won't prevent air leakage from the unconditioned basement to the conditioned space above; the large gap should be sealed with a rigid air barrier and caulked or spray foamed.

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This typical dropped ceiling hallway chase shows a complicated air sealing scheme where chase ceiling drywall meets sidewall top plates

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Wrong – Air sealing and fastening of this duct take-off has been damaged during construction, causing a large gap in the right-hand side of the connection that will reduce air delivered to living spaces and make it difficult to balance the system

Wrong – Air sealing and fastening of this duct take-off has been damaged during construction, causing a large gap in the right-hand side of the connection that will reduce air delivered to living spaces and make it difficult to balance the system

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For homes with heating registers in the ceiling or floor, air seal where the duct boots meet the ceiling drywall or the flooring to prevent heat loss around the register.

For homes with heating registers in the ceiling or floor, air seal where the duct boots meet the ceiling drywall or the flooring to prevent heat loss around the register.

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Form an insulation dam of sheet metal around a flue pipe in the attic after air sealing around the pipe with sheet metal and fire-rated caulk or canned foam

Form an insulation dam of sheet metal 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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Right – This supply duct is thoroughly sealed at all joints with mastic to prevent air leakage and the duct is equipped with a damper to provide zoned heating and cooling along with other trunk ducts.

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After connecting with sheet metal screws, this take-off collar is then air sealed and further secured using UL 181 fiber-reinforced duct sealant mastic paste.

After connecting with sheet metal screws, this take-off collar is then air sealed and further secured using UL 181 fiber-reinforced duct sealant mastic paste.

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