Extech RH390 Precision Thermohygrometer, 0 to 100% RH/, -22 to 199F

Representative image only.
Extech Mfr # RH390 – Item # EW-37803-33
Measures relative humidity with ±2% accuracy


$169.99USD / Each
$199.99USD / Each

$158.00USD / Each

for an additional
$158.00USD / Each
Time to recalibrate? Click on the calibration service to view details, then order.


Specifications & Description

  • Min RH Range (%)0
  • Max RH Range (%)100
  • RH Accuracy±2% RH
  • RH Resolution (%)0.1%
  • Min Temperature (° F)-4
  • Min Temperature (° C)-20
  • Max Temperature (° F)199
  • Max Temperature (° C)100
  • Temperature Accuracy±1.8°F (±1.0°C)
  • Temperature Resolution0.1°
  • Wet BulbYes
  • Response Time30 seconds
  • Display TypeLCD
  • Battery9V battery (1)
  • Width (in)1
  • DescriptionPrecision Thermohygrometer, 0 to 100% RH/, -22 to 199F


one 9 V battery and carrying case

More About this Item

Precision capacitance humidity sensor offers fast response. Slim design with rubberized sides for better grip and easy, one-handed operation. The dual LCD provides simultaneous display of humidity and temperature, or humidity and dew point, or humidity and wet bulb. Advanced features include data hold, min/max readings, low-battery indication, and auto power off.



by PowerReviews
Extech RH390 Precision Thermohygrometer, 0 to 100% RH/, -22 to 199F

(based on 1 review)

Reviewed by 1 customer

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(2 of 3 customers found this review helpful)


On Inspection...


from Waukesha, WI

About Me Academic/Professional Researcher

Verified Buyer


  • Accurate
  • Durable
  • Easy To Use
  • Well Calibrated
  • Works Properly


    Best Uses

    • In The Field

    Comments about Extech RH390 Precision Thermohygrometer, 0 to 100% RH/, -22 to 199F:

    Our company uses this product for attic inspections. The quick readings are incredibly helpful and essential to inspecting in a timely manner.

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    Do you have questions about this product?

    Get answers from real customers and in-house experts with AnswerBox.

    2 Questions | 2 Answers
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    • Q:

      Is this unit able to be calibrated and does it come with a certificate?
      Asked on 5/4/2011 by Anonymous

      1 answer



        This product can be calibrated to meet the standards provided by the National Institute of Standards and Technology (NIST), with the addition of P/N: 17005-00.

        Answered on 5/4/2011 by Chris from Technical Support
    • Q:

      is this device has a charger?
      Asked on 10/8/2010 by Anonymous

      1 answer

      • Staff Reviewer


        No, this item takes standard 9V batteries, there is no AC adapter currently available.

        Answered on 10/12/2010 by Jen from Technical Support
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