The core idea
Closed doors and uneven duct paths can pressurize some rooms and depressurize others.
How the mechanism works
Supply air without an adequate return path raises room pressure, while strong return flow without supply lowers it.
When it becomes relevant
Typical trigger: Heating or cooling operation with interior doors closed.
Evidence that supports this interpretation
- Door position changes airflow or noise
- Symptoms follow HVAC cycles
- One room differs consistently from adjacent rooms
Evidence that weakens it
- The system is off when symptoms occur
- The same pattern exists outdoors
- A direct moisture source explains the mark
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
Do not modify ductwork, fire doors or transfer openings without considering fire, acoustic and ventilation requirements.
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.
