Ductwork

HVAC | Plumbing | Electrical | Ductwork | Solar Hot Water Heating Systems | Grid-tied Renewable Energy Electric Systems

Your home's ducts move heated and cooled air to the living areas to make you feel comfortable. But in a typical house, 20 percent of the air that moves through the duct system is lost due to leaks, holes, and poor connections. The illustration below shows many common duct problems, such as:

A. Leaky duct connections

B. Leaky return ducts

C. Furniture blocking registers

D. Leaks at furnace and air filter slot and duct tape failures

E. Fallen duct insulation

F. Leaky supply ducts

G. Kinks in ductwork restricting airflow


Following are some duct installation best practices:

  • Duct size, design, and installation should be done per ANSI/ACCA Manual D or local equivalent.
  • The main HVAC trunk should be made of sheet metal and flex-duct take-offs should not be greater than 10 feet.
  • Ninety-degree angles in ducts should have turning vanes.
  • Duct connections should be sealed with mastic-hardcast or UL181 foil tape (not duct tape).
  • Ducts, plenums, and trunks should be insulated if they cannot be installed in a conditioned space.
  • Install air balancing dampers that are accessible.
  • Ensure that pressure is balanced for all bedrooms.
  • Eighty percent of ductwork should be located within thermal envelope and conditioned space, never in exterior walls.

Duct connections should be sealed with mastic-hardcast or UL181 foil tape, not duct tape.

  • Use return ducts or transfer grilles in each room.
  • Complete a direct duct-pressure test with an optimal leakage of less than 10 percent.
  • Mask duct outlets during construction and vacuum before running to protect indoor air quality.

FAST FACT: Approximately 70 percent of the 60 YouthBuild programs surveyed in 2005 found that avoiding installation of ductwork in exterior walls was effective.

Benefits of Energy-Efficient Ductwork

  • Reduces energy costs by 30–40 percent per year and improves comfort level.
  • The most efficient systems on the market are up to 70 percent more efficient than the current average.
  • Homeowners can qualify for a cash rebate from the local utility or be able to purchase a system with no payments or interest for up to one year in certain areas.
  • Reduces dust circulating in the house after occupancy.
  • Cleaning all ducts before occupancy increases comfort and reduces air-conditioner use.
  • Installing an attic ventilation system reduces electricity usage and moves large volumes of air to achieve comfort at higher temperatures without air conditioning.
  • Installing a greater efficiency gas furnace reduces air emissions, costs less to operate, and saves natural resources.

Behind the walls of an ENERGY STAR qualified home...

Tightly-sealed and well-insulated ducts keep you more comfortable and increase the energy efficiency of your home. Sealing also helps improve indoor air quality by reducing the risk of dust, moisture, pollen, pests, and noise from entering the ducts and circulating throughout your home.

Reprinted with permission © Building Science Corporation