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Extech RH390 Precision Thermo‑Hygrometer

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  • Humidity range: 0% to 100%
  • Humidity accuracy: +/-2%
  • Temperature range:-4° to 199°
  • Temperature accuracy: +/-1.8°
  • Also measures dew point
Availability: Typically in stock (Details)

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Product Information

The Extech RH390 features the highest 2% RH accuracy in under 30 Seconds!


The Extech RH390 Thermo-Hygrometer is well known in the restoration industry for its fast response time. It also offers operators unparalleled accuracy and durability. Comes with a carry case and 9V battery.



  • Less than 30 seconds RH response time
  • Dual, backlit display
  • Simultaneous display of:
    • Humidity/temperature
    • Humidity/dewpoint
    • Humidity/Wet Bulb
  • Slim design with rubberized sides for better grip and one-hand operation
  • Data hold and Min/Max functions
  • Auto power-off with disable and low-battery indicators
  • Comes with carrying case and 9V Battery



  • Humidity: 0 to 100%RH
  • Temperature: -4 to 199°F
  • Basic Accuracy: ±2%RH
  • Max. Resolution: 0.1%RH
  • Dewpoint: -22 to 199°F
  • Wet Bulb: 32 to 176 °F






More Information
Thermo-Hygrometer Temp Accuracy ± 1.8°F
Thermo-Hygrometer Temp Range -22° to 199°F
Thermo-Hygrometer RH Accuracy +/- 2%
Brand Extech
Thermo-Hygrometer Calculations Dew Point, Rh, Temp, Wet Bulb
Thermo-Hygrometer Temp Accuracy ± 1.8°F
Thermo-Hygrometer RH Range 0 to 100%
Category Thermo-Hygrometer
Warranty Information One (1) year from the date of purchase on parts and labor
Condition new
Manual / Schematic