Quick answer: The testo 605i measures air temperature and relative humidity. From those quantities you can estimate dew point and compare it with a separately measured wall temperature to assess surface-condensation risk.
What makes the testo 605i different
The testo 605i measures air temperature and relative humidity, allowing dew-point assessment through the companion app. It does not directly measure a wall surface or diagnose mold. For a comparable instrument-based assessment, see the testo 625 condensation and mould risk guide.
Prepare and carry out the measurement
- Measure temperature and relative humidity in a representative room location after allowing equilibration.
- Use a dew-point calculation or the supported app value; record measurement time and ventilation conditions.
- Measure the affected and unaffected wall surfaces with a suitable surface sensor or IR method that accounts for emissivity.
- Investigate recurring cold spots, duration of exposure and other moisture sources; do not diagnose mold from a single humidity reading.
Model-specific use and interpretation
Measure room temperature and RH away from a local jet or heat source, then separately check the actual wall surface with a suitable surface or IR instrument. Compare the surface temperature to the estimated dew point under matching conditions.
Condensation is physically possible when a surface reaches the local air’s dew point. Surface moisture is not guaranteed, and mold growth depends on duration, material and environmental history.
A cold wall near or below dew point indicates possible surface condensation; mold diagnosis requires inspection of duration, materials and sources of moisture.
Worked example (hypothetical)
Hypothetical room: 22 °C air at 60% RH has a dew point of approximately 14 °C. A wall area at 12 °C has potential for surface condensation; another area at 18 °C has more margin. These figures are illustrative.
Dew point and wall temperature require different sensors
The 605i provides air temperature and RH data useful for estimating dew point. It does not sense wall temperature; add a suitable surface thermometer or IR camera and verify emissivity for the surface under test. Note outdoor weather, ventilation state and furniture clearance when comparing affected and unaffected walls. Condensation risk can change hourly, and one dry reading is not a long-term mold-risk assessment. For IR-based wall-temperature checks, see the testo 872 thermal camera setup guide.
Interpretation: When air is 22 °C at about 60% RH, a wall at 12 °C is colder than the approximate 14 °C dew point; a wall at 18 °C is above it. For the underlying wall-to-wall mechanism, read why condensation forms on one wall.
Limits and safety
Follow the exact instrument manual and the equipment manufacturer’s acceptance criteria. The example is not field evidence, a legal limit or a commissioning target. Work on energized electrical equipment, combustion systems, charged refrigerant circuits or hot surfaces requires qualified personnel and the site’s approved protective procedures.