Guided evidence worksheet
Odor transfer: source location versus pressure pathway
Record fan, door, fireplace and weather state when odor begins, then compare the strongest smell location with likely source cavities.
Reasoning guardrail
Separate the routes before choosing a repair.
The room where an odor is noticed is not necessarily where the odor originates.
- Trigger
- The equipment or door position that starts the odor is a high-value clue.
- Area
- Airflow
- Provenance
- Original explanatory diagram, not a site photograph.
1. Freeze the evidence
What happened first?
2. Competing hypotheses
Record evidence for and against each route.
Pressure-driven transfer from another zone
Fans, stack effect or wind draw odor through cavities from a crawlspace, drain, garage or wall.
Evidence that raises fit
Evidence that lowers fit
Notes
Dry trap or drainage odor source
A missing water seal or pressure disturbance releases sewer gas near a fixture.
Evidence that raises fit
Evidence that lowers fit
Notes
Local damp material or microbial odor source
A wet material emits odor directly and pressure only changes where it is noticed.
Evidence that raises fit
Evidence that lowers fit
Notes
3. Decision points
Change one condition at a time.
Does operating an exhaust fan, opening a door or changing fireplace state move or intensify the odor?
Yes: Map the pressure pathway and source zone separately.
No: Inspect local drains and damp materials.
Observed answer and evidence
Does restoring water to a little-used trap stop the odor?
Yes: Investigate trap drying, siphonage or leakage.
No: Continue source isolation across cavities and adjacent zones.
Observed answer and evidence
Safety boundary
Stop rather than create a better clue.
- Leave the area and seek help for fuel gas, solvent, smoke or strong unknown chemical odor.
- Do not use flames or create sparks while investigating an unknown odor.
5. Current conclusion
