Achieving Leak-Free Ducts For Energy Code Compliance

Recent changes in the Florida Energy Code may require builders to re-evaluate energy efficiency measures included in their homes in order to pass code. One credit, the leak-free duct credit, provides a 9 percent benefit for code compliance. For comparative purposes, including this credit has about the same impact as raising the air conditioning (AC) system SEER rating from 13 to 15.  However, verification is required by a state certified energy rater.

Leak-Free Duct Credit Specifics

To receive the duct system credit, leakage must be less than 3 percent Total Duct Leakage (3 cfm/100 square feet). Or the leakage must be less than 9 percent Total Duct Leakage, and less than 3 percent leakage to unconditioned spaces (Out Leakage). Since less than 3 percent Total Duct Leakage is extremely difficult to achieve (air handlers alone leak 1-3 percent), only the second option, 9 percent Total Duct Leakage with 3 percent Out Leakage, will be covered in this article.  Sampling is prohibited for receiving this energy code credit.

A blower door must be used in conjunction with a duct tester to measure Out Leakage. The duct tester alone is used to measure Total Duct Leakage. The blower door-duct tester combination is required to test for the practical and achievable option. No substitutes for estimating duct leakage (such as pressure pan testing) are allowed. When claiming the duct leakage credit, measurements entered into the state’s duct compliance form and general energy code compliance form (Form 600A) must be submitted to the building department and signed by both the rater of record and building official.

Effort to receive the Leak-Free Duct Credit

Although the credit is reasonable and achievable, it is by no means automatic. Conscientious efforts must be taken to identify areas of leakage early-on, prior to final system testing. Detecting and fixing problems at rough-in can be both a time and cost-saver. Once the final installation is complete, a leakage test is performed on the entire air distribution system, including the air handler enclosure, to verify that the system meets the duct leakage credit specifications.

Smoke testing the ductwork at rough-in will identify leaks and allow duct installers to remediate any failures early on. Smoke testing involves temporarily sealing the register boxes and introducing theatrical fog into the duct system under slight pressure.  Previously invisible leaks can be identified easily and repaired with this qualitative testing method. This step is imperative, since a failure at final testing will be costly, difficult to remediate and delay the CO. Other advantages of performing a smoke test at rough-in include:

• Better home comfort, lower operating costs and fewer client call-backs.
• Reduced installation costs by remediating problems at rough-in.
• Improved installation quality control, therefore creating an optimal performing duct system.
• Protection of duct system from contamination because temporary seals remaining on registers throughout construction.
• Improved indoor air quality and home durability and reduced health and safety problems associated with duct leakage.
• Better subcontractor performance, since work is thoroughly inspected and failures remediated.
• Complementary effort to demand side management and energy efficiency programs which require specific duct leakage results for program participation.