Duct Leakage Testing - 11/15/2004 - House Energy Efficiency Insulation

Duct Leakage Testing

Leaky ducts can be a significant source of energy waste in both new and existing homes.

There are over a million miles of forced-air ductwork in American homes. If ducts leak, and most do, energy is wasted. Leaky ducts can be a significant source of energy waste in both new and existing homes.

Leaky supply ducts can send expensive conditioned air into unconditioned spaces such as attics and crawlspaces and leaky return ducts can draw unconditioned air into the duct system. Leaky ducts can be responsible for inadequate air distribution, resulting in rooms that are too cold or too warm. Simple duct sealing methods can save energy and increase comfort.

Duct leakage measurements are used to diagnose duct leakage problems, estimate energy loss from duct leaks, and verify the quality of duct system installation. Energy professionals can use duct testing equipment or a blower door to determine how leaky, or energy-inefficient, a duct system is.

Ducts can be tested for air tightness by a few different methods. The most common method is to pressurize the duct system with a calibrated fan, much in the same way a plumbing system is pressure tested for leaks. In this method, supply registers are sealed off and the ductwork is pressurized with a special fan. The rate of airflow (usually expressed in cubic feet per minute at 25 Pascals of pressure) into the ducts (with the registers sealed) is used to determine the duct tightness.

A second method for testing duct losses is to use a blower door only. In this case, the house is pressurized with the air supply registers open and then again with the registers sealed off (with special covers). The difference in the numbers represents duct loss.

A third method involves using a blower door and a duct fan. The house and duct system are pressurized to the same level, thereby canceling the effect of leaks to the interior. The measured fan flow in this method represents duct leakage to the exterior.

A fourth method, called DeltaQ, was recently developed by researchers at Lawrence Berkeley Laboratory. It uses a blower door only and tests the home with the air handler on and off. A curve fit analysis is used to determine duct leakage.

	Energy professionals can use duct testing equipment or a blower door to determine how leaky, or energy-inefficient, a duct system is. Contractors are available nationwide that use blower doors and other equipment to measure air leakage and diagnose air quality, comfort and structural problems.
	Leaky ducts can be a significant source of energy waste. Simple duct sealing methods can save energy and increase comfort.

Not Applicable

Not Applicable

Two standards from ASTM International cover testing methods:

• ASTM E1554-03. Standard Test Methods for Determining External Air Leakage of Air Distribution Systems by Fan Pressurization.
• ASTM E779-03. Standard Test Method for Determining Air Leakage Rate by Fan Pressurization.

Not Applicable

To perform a duct pressurization test, an energy professional connects a duct testing machine to a duct system at the air handler or a central return grille. All other return grilles and supply registers are temporarily sealed. The fan is turned on and flow is increased until the duct system is pressurized to the specified test pressure (typically 25 Pascals). The contractor measures leakage rate using an airflow and pressure gauge. If desired, theatrical fog can be injected in the systems to determine the exact location of leaks and to demonstrate duct leakage to homeowners.

The calibrated fan takes precise measurements of leakiness over a wide range of airflows.

Not Applicable

The duct pressurization test is a relatively inexpensive, simple, and accurate diagnostic method that requires only one piece of equipment. Low flows can be measured precisely. Tests can be performed on new homes before drywall is installed--making duct sealing an easier task. Studies estimate that fixing leaky ductwork can save up to 25 percent on energy costs.

Duct testing equipment typically costs about $2000 or less. However, that cost will double if a method is selected that uses two pieces of equipment. A duct diagnostic test for new home construction typically will cost between $175 and $400. Check with your local utility to see if they offer free or discounted diagnostic tests.