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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.

Preparation
The entire length of the duct system (e.g., in the attic, basement, or crawlspace) shall be inspected and all damaged or disconnected ducts shall be repaired or replaced. All flexible ducts with sharp bends shall be rerouted or replaced; ducts with excessive length shall be cut to the proper length; and supports shall be added for sagging ducts to achieve the straightest path possible.
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 ½ 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 or UL 181 tape used in strict accordance with manufacturer’s instructions.
If the air filter is installed in a filter media box attached to the air handler, the access panel for the filter should be fitted with a flexible, air-tight gasket to prevent air leakage.
Duct boots shall be sealed to finished surfaces (e.g., drywall) with caulk or other sealants per duct manufacturer’s instructions.
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.
Disturbance to attic, crawlspace, basement, or wall insulation shall be minimized during duct sealing and insulating work and all damaged insulation shall be repaired or replenished back to original levels and condition.
A MERV 8 or higher filter shall be installed. Air flow across the coil shall be measured and verified to be within 15% of design airflow.
Commissioning
After ducts are sealed, leakage testing shall be performed in accordance with RESNET Standard Chapter 8 or ACCA Standard 5 and the results shall be provided to the homeowner to verify that duct leakage has been reduced 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 and adjustments shall be made with all bedroom doors closed to identify any imbalances equal to or greater than 5 pascals. Where this level of pressure differential is identified, transfer grilles or jump ducts shall be provided where bedrooms adjoin hallways. The transfer duct opening should be sized to equal 1 square inch of free opening area per CFM of supply air provided to the bedroom.

BASC Guides

This guide can help you assess an existing Heating, Ventilation and Air Conditioning (HVAC) system for potential intervention such as repair, upgrade or expansion, or replacement.

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 describing repair and reconfiguration of air handler closet and platform when replacing air handler.

Guide describing how to conduct duct leakage tests per RESNET protocols.

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert (HIE) 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:

  • Be the Expert: Take advantage of Building America Solution Center comprehensive guidance on ‘Existing Home’ retrofits.
  • Earn Trust: Inform homeowners how your work conforms to U.S. Department of Energy (DOE) world-class expert guidance and recommend homeowners visit the DOE website as evidence these are indeed official best practices.
  • Clarity with Contrast: Tell prospective homeowner clients to compare your expert recommended best practices with other contractors.
  • Ensure Equivalent Pricing: Tell prospective homeowner clients to insist other bids also include DOE checklists to ensure equivalent quality work.
  • Translate Value: Note your company uses DOE HIE Checklists based on world-class expert recommendations for home improvements on all your public-facing communication including websites, advertising, and signage.
  • Create Emotional Experiences: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images for good and bad insulation and air sealing; pre- and post-energy bills following quality installed work; short and long warranties for standard and high-efficiency equipment; and charts showing amounts of contaminants in homes that can be reduced with effective fresh air systems.

Duct Sealing and Insulation Background

Sealed ducts

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.