Define the question before measuring
Leaky ducts can draw attic, crawlspace or wall-cavity air into the system or push conditioned air into concealed spaces.
Capture a useful baseline
Record the exact location, date, current weather or equipment state, recent activities and the first visible, audible, sensory or measurable change. Keep one unaffected reference point.
Safe observations to repeat
- Log system on/off timing
- Compare affected and unaffected supply outlets
- Inspect only accessible ducts without disturbing suspect materials
Compare supporting and weakening evidence
Supports the pathway
- Odor or dust follows fan cycles
- Rooms near specific ducts differ
- Accessible ducts show damaged joints or insulation
Weakens the pathway
- The symptom is independent of fan operation
- No ducts pass near the affected area
- A local source is directly visible
Interpret the result conservatively
Look for a repeatable relationship between trigger, location, timing and change. Treat exceptions as useful evidence rather than forcing every event into one explanation.
Escalation boundary
Duct testing and repair in contaminated or inaccessible cavities should be handled by qualified professionals.
Close the loop
If work is performed, repeat the same observation under a comparable trigger and through the original lag window. Record both recurrence and non-recurrence events.
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.
