The core idea
Leaky ducts can draw attic, crawlspace or wall-cavity air into the system or push conditioned air into concealed spaces.
How the mechanism works
Pressure inside ducts differs from surrounding cavities, so defects become transport paths for heat, moisture, dust and odors.
When it becomes relevant
Typical trigger: HVAC fan operation, filter changes or seasonal system startup.
Evidence that supports this interpretation
- Odor or dust follows fan cycles
- Rooms near specific ducts differ
- Accessible ducts show damaged joints or insulation
Evidence that weakens it
- The symptom is independent of fan operation
- No ducts pass near the affected area
- A local source is directly visible
What this concept cannot prove alone
A single observation, image or meter reading cannot confirm the complete failure pathway. Use this concept to form better questions, compare alternatives and decide which safe observation would be most informative next.
Safety and professional boundary
Duct testing and repair in contaminated or inaccessible cavities should be handled by qualified professionals.
Primary references for this topic family
These references ground the general building-science or safety context. They do not diagnose a specific house, replace local requirements or certify a repair.
