Thermal Imager Delta-T Reference
Typical surface-temperature differentials for moisture, insulation, and electrical hotspots.
Reference
Scenarios
- Moisture intrusion behind drywall 2 to 5Note: Wet substrate cools the surface relative to surrounding dry areas; difference grows with evaporation.
- Missing or compressed insulation 3 to 10Note: Heat-flow gradient through the assembly creates a visible thermal pattern at the cavity boundary.
- Active leak around penetration 3 to 8Note: Cool tail downstream of the leak path; reflects evaporative cooling and conductive loss.
- Electrical hotspot (loose lug, overloaded conductor) 10 to 50+Note: Compare phase to phase under load; a single hot lug indicates a loose or oxidized connection.
- Bearing or motor overheating 10 to 30Note: Compare to ambient and similar units; trend over time matters more than a single reading.
Checked against published worked examples from: IICRC S500 + ASHRAE-bundled thermal-delta-T scenarios.
Details, formula, and sources
Formula or table(reference page; no compute) Thermal-imager delta-T interpretation: compare inspected component temperature against an unloaded reference of the same construction; a surface 1 °C or more BELOW a dry reference of the same construction flags moisture (evaporative cooling); 5-10 °C differences flag an active issue per IR-imaging engineering practice.
Source and editionASTM C1153 (Standard Practice for Location of Wet Insulation in Roofing Systems) by name; FLIR / Fluke published thermography training materials.
Free accessASTM licensed; training overviews free at flir.com / fluke.com / infraredtraining.com.
What governsEstimate. AHJ and licensed professional govern.