Kestrel 4400 Pocket Heat Stress Tracker | RPR Ltd
Kestrel 4400 Pocket Heat Stress Tracker Kestrel 4400 Pocket Heat Stress Tracker
5-Year Warranty on all Kestrels

Kestrel 4400 Pocket Heat Stress Tracker

Product code: K4400 - 0844

£0.00 inc. VAT

This product has now been superseded by the Kestrel 5400, which is available here »

The Kestrel 4400 is a portable handheld device that provides waterless WBGT measurements and displays an on-screen warning signal when environmental conditions enter a danger zone, used by athletes in training, military personnel, firefighters and anyone working in potentially hot environments or implementing a heat stress management plan . The Kestrel 4400 has all the features of the Kestrel 4000; a comprehensive weather instrument offering an accurate measurement of wind speed, temperature, humidity and barometric pressure, but it also provides Wet Bulb Globe Temperature, thermal work limits, globe temperature and naturally aspirated wet bulb temperature, which determine the heat strain on human performance.

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The Kestrel 4400 comes in a handy transportable miniature briefcase with the Kestrel vane mount which allows the unit to be mounted on a tripod for longer-term monitoring and logging of heat stress conditions.

At the touch of a button environmental conditions are clearly shown in digital or graphical form. Individual functions can be displayed in a choice of three different formats either as a current reading or a minimum/maximum/average reading or a chart display. There are also three user screens, which can be customised to simultaneously display the three most appropriate functions for the application.

The Kestrel 4400 can be set up to log data manually or automatically at programmable intervals in order to display a history of weather information. Graphs display up to 2400 data points and the value, time, date of capture point can be shown.

The stored data can also be uploaded to a PC, for analysis/storage with the optional Kestrel Interface and Communicator software. With the Bluetooth® model, data may be streamed live via Bluetooth wireless technology.

High precision Zytel® bearings and a lightweight impeller provide accurate air flow measurements and the ability to operate at speeds as low as 0.6m/s. The impeller is user-replaceable in case of damage, also ensuring high accuracy levels are maintained for life. An integral flip-open hard cover protects the impeller when not in use which is particularly helpful when using other functions.

A precision external thermistor sensor provides fast response temperature readings and accuracy of +/- 1°C. The 0.1 degree resolution of the display aids in determining when a consistent reading has been reached. A special housing protects the relative humidity sensor from contamination providing an accuracy of +/-3%.

A monolithic silicon based pressure sensor enables barometric pressure and altitude to be calculated with a resolution of 0.1mb and 1m respectively.

The Kestrel 4400 also has a 1" black globe with a thermometer in the centre. This thermometer reads the temperature of the black globe which indicates the radiant heat exposure of one in sunlight. Also built into the Kestrel 4400 are advanced algorithms to calculate the wet bulb globe temperature (WBGT).

All text on the Kestrel can be displayed in a choice of five different languages, with a choice of English, French, Italian, Spanish or German.

The Kestrel 4400 is powered by two easily replaceable AAA batteries which enjoy prolonged battery life averaging around 400 hours, due to two power saving modes integral within the Kestrel settings.

And finally, the Kestrel 4400 comes with a 5 year limited manufacturers warranty from date of purchase.

Kestrel 4400 measures
  • Wet Bulb Globe Temperature (WBGT)
  • Thermal Work Limit (TWL)
  • Naturally Aspirated Wet Bulb Temperature
  • Globe Temperature
  • Mean Radiant Temperature (MRT)
Kestrel 4400 also measures
  • Current wind speed
  • Average wind speed
  • Maximum wind speed
  • Air, water & snow temperature
  • Wind Chill
  • Heat index
  • Dew Point
  • Relative Humidity
  • Barometric pressure
  • Altitude
  • Density altitude
  • Wet bulb temperature
  • Time & Date
Choice of measurement units
  • kt, m/s, km/h, mph, ft/min, Beaufort
  • °C, °F
  • %
  • mbar, inHg, hPa, psi
  • m, ft
  • Speed ±3% of reading or ±0.1m/s
  • Temperature ±1°C
  • Relative humidity ±3%
  • Dew point ±2°C
  • Barometric pressure ±1.5mbar
  • Altitude ±15m
Operational Range
  • Speed 0.6 to 60 m/s
  • Temperature -45 to +125°C
  • Relative humidity 0 to 100%
  • Barometric pressure 10 to 1100mbar
Specification Range
  • Speed 0.6 to 40 m/s
  • Temperature -29 to +70°C
  • Relative humidity 5 to 95%
  • Barometric pressure 750 to 1100mbar
Available options
Kestrel 4400 features
  • Multi-function instrument
  • Small and easy to handle
  • Waterless Wet Bulb Globe Temperature (WBGT)
  • Exterior temperature, humidity and pressure sensors for fast, accurate readings
  • Graphical three-line displays
  • Data capture up to 2300 readings
  • Minimum/maximum/average values
  • User defined screens
  • Language selection from English, French, Spanish, German and Italian
  • Compact, rugged design
  • High accuracy
  • High precision axle and low-friction Zytel bearings
  • User-replaceable impeller
  • Flip-top hard cover protects impeller while using other functions
  • Easy to read, back-lit display
  • Runs from 2 AAA batteries
  • Data upload (with optional PC interface or integrated Bluetooth wireless technology)
  • Waterproof and floats
  • Drop tested
  • Tripod mountable with vane mount accessory
  • Available in safety orange
  • 5 year warranty
Typical applications
  • Mining industry
  • Military
  • Health and safety in the workplace
  • Fire fighters
  • Sporting events. For example, The American College of Sports Medicine recommend event cancellation when Wet Bulb Globe Temperature goes over their published thresholds
Heat Stress

Human heat stress results from a combination of many environmental factors - air temperature and humidity along with radiant heat from the sun and surfaces, balanced by the cooling effect of breezes or air flow. The most common composite measurement used to determine appropriate exposure to heat stress conditions is Wet Bulb Globe Temperature or WBGT.

The Kestrel 4400 Heat Stress Tracker Provides Waterless WBGT Measurement

Until now, most accurate WBGT measurement tools were large, cumbersome to use (requiring the transport of distilled water along with the measurement unit) and/or expensive. NK have added a compact black globe thermometer to the already proven sensor suite of the Kestrel 4000 Pocket Weather Tracker, then built in advanced algorithms to calculate WBGT values within 2.2 deg C of the values obtained from a full-sized WBGT setup.

The Kestrel 4400 Heat Stress Tracker uses a 1" Black Globe which is calibrated to achieve the same measurements as a 6" globe.

The Kestrel 4400 Pocket Heat Stress Tracker fits in a pocket or small Kestrel Belt Carry Case and provides accurate waterless WBGT measurements within minutes of exposure to the air.

TWL and Other Key Measurements

The Kestrel 4400 also displays thermal work limit (TWL), another recognised composite heat stress prediction tool. For both WBGT and TWL, the Kestrel 4400 provides on-screen alarms when conditions enter the caution and danger zones, providing clear and immediate guidance that heat illness prevention steps must be taken. Clothing levels can also be customised, making the Kestrel 4400 particularly useful in activities requiring heavy protective gear which worsens heat stress. The Kestrel 4400 also displays natural wet bulb temperature, black globe temperature, and mean radiant temperature (MRT).

Primary Measurement Units Resolution Accuracy
(if less)
Wind Speed
or Air Velocity
m/s 0.1 Larger of 3% of reading, least significant digit or 20 ft/min 0.6 to 60.0 m/s
0.6 to 40.0 m/s
1 inch diameter impeller with precision axle and low-friction Zytel® bearings.
Start-up speed stated as lower limit, readings may be taken down to 0.4 m/s | 79 ft/min | 1.5 km/h | .9 mph | .8 kt after impeller start-up.
Off-axis accuracy -1% @ 5° off-axis; -2% @ 10°; -3% @ 15°.
Calibration drift < 1% after 100 hours use at 16 MPH | 7 m/s.
Replacement impeller (NK PN-0801) field installs without tools (US Patent 5,783,753).
ft/min 1 18 to 11,811 ft/min
118 to 7,874 ft/min
km/h 0.1 2.2 to 216.0 km/h
2.2 to 144.0 km/h
mph 0.1 1.3 to 134.2 mph
1.3 to 89.5 mph
knots 0.1 1.2 to 116.6 knots
1.2 to 77.8 knots
Beaufort 1 0 to 12 B
Temperature °F 0.1 1.8 °F 14.0 to 131.0
-20.0 to 158.0
Air, water or snow temperature. Hermetically-sealed, precision thermistor mounted externally and thermally isolated (US Patent 5,939,645) for rapid response. Airflow of 2.2 mph | 1 m/s or greater provides fastest response and reduction of insulation effect. Calibration drift negligible.
°C 0.1 1.0 °C -10.0 to 55.0
-29.0 to 70.0
Globe Temperature °F 0.1 2.5 °F -14.0 to 131.0
-20.0 to 140.0
Temperature inside 1inch|25mm black powder coated copper globe converted to Tg equivalent for standard 6inch|150mm globe. Closest equivalence obtained with airflow greater than 2.2mph|1m/s.
°C 0.1 1.4 °C -10.0 to 55.0
-29.0 to 60.0
Relative Humidity %RH 0.1 3.0 %RH 0.0 to 100.0%
5.0 to 95.0% non-condensing
Polymer capacitive humidity sensor mounted in thin-walled chamber external to case for rapid, accurate response (US Patent 6,257,074). To achieve stated accuracy, unit must be permitted to equilibrate to external temperature when exposed to large, rapid temperature changes and be kept out of direct sunlight. Calibration drift +/- 2% over 24 months. RH may be recalibrated at factory or in field using Kestrel Humidity Calibration Kit (NK PN-0802).
Pressure inHg 0.01 typical 0.04 inHg
max 0.07 inHg
0.30 to 32.48 inHg Air pressure at the location. Adjustable reference altitude allows display of station pressure or barometric pressure corrected to MSL. Monolithic silicon piezoresistive pressure sensor with second-order temperature correction. Pressure sensor may be recalibrated at factory or in field. Kestrel 2500 and 3500 display continuously updating three-hour barometric pressure trend indicator: rising rapidly, rising, steady, falling, falling rapidly. Kestrel 4000 series displays pressure trend through graphing function.
hPa (mb) 0.1 typical 1.5 hPa
max 2.5 hPa
300.0 to 1100.0 hPa 10.0 to 1100.0 hPa
PSI 0.01 typical 0.02 PSI
max 0.04 PSI
0.14 to 15.95 PSI
Wind Chill °F 0.1 1.8 °F Refer to stated ranges for wind speed and temp. Perceived temperature resulting from combined effect of wind speed and temperature. Calculated based on the NWS Wind Chill Temperature (WCT) Index, revised 2001, with wind speed adjusted by a factor of 1.5 to yield equivalent results to wind speed measured at 10 m above ground. Specification temperature limits established by WCT Tables.
°C 0.1 1.0 °C
Heat Index °F 0.1 3.6 °F Refer to stated ranges for temp. and relative humidity. Perceived temperature resulting from the combined effect of temperature and relative humidity. Calculated based on NWS Heat Index (HI) tables. (Specification temperature limits established by HI tables.)
°C 0.1 2.0 °C
Thermal Work Limit (TWL) W/m2 0.1 10.9 W/m2 Refer to stated ranges for wind speed, temp., globe temp, relative humidity and pressure Estimated safe maximum continuously sustainable human metabolic rate (W/m2) for the conditions and clothing factors. Based off of estimated metabolic output of typical human. On-screen zone warnings.
Outdoor Wet Bulb Globe Temperature(WBGT) °F 0.1 1.3 °F Refer to stated ranges for wind speed, temp., globe temp, relative humidity and pressure Measure of human heat stress defined as the combination of effects due to radiation, convection, and conduction. Outdoor WBGT is calculated from a weighted sum of natural wet bulb (Tnwb), globe temperature (Tg), and dry bulb temperature (Td). User settable on-screen warning zones.
°C 0.1 0.7 °C
Wet Bulb Temperature - Naturally Aspirated (Tnwb) °F 0.1 1.4 °F Refer to stated ranges for wind speed, temp., globe temp, relative humidity and pressure Similar to psychrometric wet-bulb temperature (see below). However, Tnwb only undergoes forced convection from the ambient air velocity. Tnwb is a measure of the evaporative cooling that the air will allow. This is accounted for by combining the effects of, mainly, relative humidity and wind speed.
°C 0.1 0.8 °C
Wet Bulb Temperature (Psychrometric) °F 0.1 3.2 °F Refer to stated ranges for temp., relative humidity and pressure. Temperature indicated by a sling psychrometer. Due to nature of the psychrometric ratio for a water-air system, this approximates the thermodynamic wet-bulb temperature. The thermodynamic wet-bulb temperature is the temperature a parcel of air would have if cooled adiabatically to saturation temperature via water evaporating into it.
°C 0.1 1.8 °C
Dewpoint °F 0.1 3.6 °F Refer to stated ranges for temp. and relative humidity. Temperature to which the air must be cooled at a constant pressure for water vapour to condense into water. Calculated from temperature and relative humidity.
°C 0.1 2.0 °C
Altitude ft1 typical 50 ft
max 98 ft
-2,300 to 85,000 ft Height above Mean Sea Level ("MSL"). Temperature compensated pressure (barometric) altimeter requires accurate reference barometric pressure to produce maximum absolute accuracy.
m 1 typical 15 m
max 30 m
-700 to 25,900 m
Density Altitude ft 1 246 Refer to stated ranges for temp., relative humidity and pressure. Air density converted to equivalent sea level elevation at the International Standard Atmosphere. Calculated from temperature, pressure and relative humidity.
m 1 75
Max/Avg Wind Max and average wind calculation may be started and stopped independently of data logging of other values, along with all other wind-related functions: air velocity, crosswind, headwind/tailwind, wind chill, WBGT, TWL, evaporation rate.
Data Storage & Graphical Display, Min/Max/Avg History Minimum, maximum, average and logged history stored and displayed for every measured value. Large capacity data logger with graphical display. Manual and auto data storage. Min/Max/Avg history may be reset independently. Auto-store interval settable from 2 seconds to 12 hours, overwrite on or off. Logs even when display off except for 2 and 5 second intervals (code version 4.18 and later). Data set capacity = 2300.
Data Upload Requires optional PC interface (USB or RS-232) or Bluetooth enabled model and provided software.
Available Bluetooth®
Data Connect
Adjustable power consumption and radio range from up to 30 ft | 9 meters. Individual unit ID and 4-digit PIN code pre-programmed for easy identification and data security when pairing and transmitting. Employs Bluetooth Serial Port Protocol for data transmission.
Display & Backlight Multifunction, multi-digit monochrome dot-matrix display. Choice of aviation green or visible red (NV models only) electroluminescent backlight. Automatic or manual activation.
Response Time & Display Update All measurements except those based on relative humidity respond accurately within 1 second. Relative humidity and all measurements which include RH in their calculation may require as long as 1 minute to fully equilibrate to a large change in the measurement environment. Display updates every 1 second.
Clock / Calendar Real-time hours:minutes:seconds clock, calendar, automatic leap-year adjustment.
Operational & Storage Temperature Range The operational temperature range of the liquid crystal display and batteries is 14° F to 131° F / -10 °C to 55 °C. Measurements beyond the operational range can be taken by briefly exposing unit to extreme conditions such that the display and batteries remain within the operational range. Storage range -22 °F to 140 °F / -30 °C to 60 °C.
Auto Shutdown User-selectable -- 15 or 60 minutes with no key presses or disabled.
Languages English, French, German, Italian, Spanish.
Certifications CE certified, RoHS and WEEE compliant. Individually tested to NIST-traceable standards (written certificate of tests available at additional charge).
Battery AAA Alkaline, two, included. Average life, 400 hours of use, reduced by backlight or Bluetooth radio transmission use.
Environmental Waterproof (IP67 and NEMA-6). MIL-STD-810F, Transit Shock, Method 516.5 Procedure IV; unit only; impact may damage replaceable impeller.
Size & Weight 6.5 x 2.3 x 1.1 in / 16.5 x 5.9 x 2.8 cm, 4.4 oz / 125 g.

The manufacturer reserves the right to amend the specification and therefore the information in this document may be subject to change