Sealing Air Ducts

In a typical home with air distribution ducts, about 15% of the costs of heating and air conditioning is due to leaks between the air ducts and the exterior.

Air leakage from air supply ducts to the exterior can waste large amounts of heated or cooled air and cause a home's interior air pressure to be lower than the outdoor air pressure.

Air leakage from the exterior into air return ducts can pull-in excessive amounts of outside air and cause a home's interior air pressure to excessively higher than the outdoor air pressure.

Test Procedure

This test should be done when the wind is calm.

1. Open all interior doors.
2. Turn the forced-air furnace or air conditioner fan on.
3. Extend a hose from the Pressure-Detective to the exterior. This can be done by:

• Drilling a 1" diameter hole in an outer wall, or
• Extending the hose out through a slightly opened window. If you choose this option, use wide tape to seal the remainder of the opening.

4. If  indoor air pressure is less than outdoor air pressure, the air-supply duct leakage to the exterior is greater than air-return duct leakage from the exterior.
5. If  indoor air pressure is greater than outdoor air pressure, the air-return duct leakage to the exterior is greater than air-supply duct leakage from the exterior.

Additional Sources of Information:

• Leaky Air Ducts Suck In Health Hazards

• Air Duct Leakage Testing: Is There a Thief in Your Ductwork?

• An Introduction to Residential Air Duct Systems

• Retrotec air leakage testing and measurement equipment

• Duct Leakage — Infiltec

• Duct Sealing — EPA Energy Star Program

• Materials for Sealing Air Ducts

• Duct Sealant Longevity

• Duct Systems in Southwestern Homes: Problems and Opportunities

• Introduction to Blower Doors