For years, Americans who would never put up with leaky plumbing pipes have been willing to accept leaky ducts. While water damage is hard to ignore, the damage caused by leaky ducts is more subtle. Yet leaky ducts not only waste huge amounts of energy — they can also lead to comfort complaints, moisture problems, mold, and rot.
Most green certification programs require builders to pay attention to duct tightness. Now that duct testing requirements are starting to appear in some local building codes, more and more builders are asking questions about the ins and outs of duct leakage testing.
If you’ve never had to worry about duct tightness before, you may want to read the “Forced Air” section of the GBA Encyclopedia.
Most green builders already know their duct basics:
A good duct system:
Although model codes have included duct-sealing requirements for years, enforcement has been spotty or nonexistent. For example, a 2001 study of 80 new homes in Fort Collins, Colorado, found that the number of homes that complied with code duct-tightness requirements was zero. Astonishingly, the average duct leakage in the studied homes was 75% of total system airflow.
Another 2001 study found that Massachusetts Energy Code requirements for duct sealing were widely ignored. Researchers who inspected 186 new Massachusetts homes reported that “serious problems were found in the quality of duct sealing in about 80% of these houses.”
The 2006 International Residential Code (IRC) requires (in section N1103.2.2) that “Ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed.” Elsewhere, in section M1601.3.1, the IRC requires that “Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing or other approved closure systems.” Hardware-store duct tape is not an approved tape.
Builders will soon need to get up to speed on duct testing, since recent…