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Duct Sealing and Insulation

Properly sealed and insulated heating and cooling ducts can reduce your utility bills by 20% while improving comfort, health, and durability.

Air ducts distribute conditioned air from your central heating and cooling equipment to warm and cool your home. However, they are often poorly sealed and under-insulated. Leaky supply ducts can lead to potential moisture-related problems as well as higher utility bills. Leaky return ducts located in unconditioned spaces can draw in hot and cold air along with dust, pollen, moisture, soil gases, and pests, which can increase utility bills while reducing the air quality in your home. That’s why sealing and insulating your ducts effectively is critically important, especially if they are located in an unconditioned attic, basement, or crawl space.

Checklist

This U.S. Department of Energy checklist includes important specifications that can contribute to a complete and quality installation. All work shall comply with these specifications, all relevant codes and standards, and all manufacturer installation instructions. The contractor shall check each box on the checklist below and sign and date at the bottom to certify the work is completed.

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Preparation


The entire length of the duct system (e.g., in the attic, basement, or crawlspace) shall be inspected and damaged ducts shall be repaired or replaced. Flexible ducts with excessive length shall be cut to proper length and sharp bends shall be corrected so bends are greater than or equal to one duct diameter radius.

All unsupported horizontal duct runs shall be supported with hanger strap or saddle supports that are at least 1.5 inches wide and spaced no more than 4 feet apart, in accordance with the Air Conditioning Contractors of America (ACCA) Manual D and manufacturer’s recommendations. Additional supports shall be provided before and after sharp bends in the ductwork. The maximum permissible sag between supports shall be 1⁄2 inch per foot.

Before sealing the ducts, leakage testing shall be performed in accordance with Residential Energy Services Network (RESNET) Standard Chapter 8 or ACCA Standard 5. Based on this pre-test, a targeted maximum level of duct leakage shall be determined and provided to the owner, preferably 10% or less of total air flow.

Airflow shall be measured at each register with a powered fl ow hood as specified in the RESNET Standard Chapter 8 to help determine likely locations of leaks or damage.

Installation


All duct leaks, connections, and plenums shall be sealed with UL-approved mastic, UL 181 tape, or equivalent (e.g., aersol sealant) used in strict accordance with manufacturer’s instructions.

If the air filter is installed in a filter box attached to the air handler, the filter access panel should be fitted with an air-tight gasket.

Duct boots in unconditioned spaces shall be sealed to finished surfaces with caulk, spray foam, or other approved sealants.

All accessible ducts in unconditioned areas (attics, crawlspaces, basements, and garages) shall be insulated to ≥ R-8 for supply ducts and ≥ R-6 for return ducts.

Insulation moved during duct sealing and insulating shall be replenished to levels that meet or exceed pre-retrofit levels.

A MERV 8 or higher filter shall be installed in the filter rack.

Commissioning


After the ducts are sealed, air leakage shall be tested per RESNET Standard Chapter 8 or ACCA Standard 5 and results provided to homeowner to verify that duct leakage is less than or equal to the target level, preferably 10% or less of total air flow.

Air flow across the coil shall be tested following procedures approved by ANSI/ACCA Standard 5 QI-2015 to verify it is within the CFM range specified by the equipment manufacturer. If it is not, adjustments shall be made by a qualified HVAC contractor.

A pressure balance test shall be performed with bedroom doors closed. Where pressure differentials are ≥ 5 Pascals, transfer grills or jump ducts shall be installed with openings equal to 1 in.2 free opening per CFM of supply air to the bedroom. Jump duct boots shall be sealed to finished surfaces with caulk, spray foam, or other approved sealants.
Duct Sealing and Insulation

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

Trust Matters: Inform homeowners how your work conforms to this world-class expert guidance. Recommend they visit the DOE website as evidence these are indeed official best practices.

Knowledge Matters: Take advantage of the Building America Solution Center as a resource for becoming an expert on these projects.

Clarity Matters: Tell prospective clients to contrast your expert-recommended best practices with other contractors.

Value Matters: Advise prospective clients to insist other bids also include these checklists to ensure equivalent quality work.

Message Matters: Showcase on your website and marketing materials that your company uses the highest quality best practices specified on HIE Checklists.

Experiences Matter: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images; pre- and post-energy bills; short and long warranties; and simple charts and graphics depicting performance advantages.

Related Guides

Guide:

Pre-Retrofit Assessment of Existing HVAC Systems

Description
Information guide describing options to consider when retrofitting or upgrading a home's HVAC system.
Guide:

Injected Spray Sealant for Existing HVAC Ducts

Description
Guide describing how to thoroughly seal HVAC ducts to ensure air delivery without leakage, and to ensure economical and quiet performance of the HVAC system.
Guide:

Air Sealing the Air Handler Closet

Description
Guide describing the repair and reconfiguration of the air handler closet and platform when replacing the air handler.
Guide:

Total Duct Leakage Tests

Description
Guide describing how to conduct HVAC duct leakage tests for total system duct leakage per RESNET protocols.

Disclaimer

This content is a work created with funding provided by the United States Department of Energy under Contract no DE-AC05-076RL01830 for the operation of Pacific Northwest National Laboratory. The information and guidance provided by Pacific Northwest National Laboratory (PNNL) in the content are intended solely for educational purposes only and do not constitute formal training or certification. It is provided with the explicit understanding that neither the United States Government nor the United States Department of Energy, nor the Contractor, nor any or their employees, nor any jurisdiction or organization that has cooperated in the development of these materials, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, software, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Viewers assumes full responsibility for all actions that they may take from information provided in this content including ensuring the safety, code compliance, and proper functionality of any products they choose to install. Installation and use of such products should be performed in accordance with local regulations and manufacturer instructions.