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.
Most green builders already know their duct basics:
- Duct leaks are very common; in many homes, duct leaks are responsible for significant energy losses.
- For ducts located in an unconditioned attic, any leaks in the supply system tend to depressurize a house, while return-system leaks tend to pressurize a house. Either condition can cause problems.
- Duct leaks outside of a home’s thermal envelope waste more energy than duct leaks inside a home’s thermal envelope.
- Even if ducts are located inside of a home’s thermal envelope, duct leaks can still connect to the outdoors. For example, supply system leaks in a ceiling between the first and second floors of a two-story home can pressurize the joist bay, forcing conditioned air outdoors through cracks in the rim joist area.
- It’s much easier to seal duct seams during new construction than in an existing house.
Characteristics of a good duct system
A good duct system: