Foil heat flux sensor with thermal spreaders, flexible, 50 x 50 mm, with temperature sensor

FHF04 is the latest standard model for general-purpose heat flux measurement. Significantly thinner and more flexible, FHF04 replaces earlier models FHF01 and FHF02. FHF04 is very versatile: it has an integrated temperature sensor and thermal spreaders to reduce thermal conductivity dependence. It is applicable over a temperature range from –70 to +120 °C. FHF04 measures heat flux from conduction, radiation and convection. Optionally, black BLK and gold GLD stickers are available to separately determine heat transport by radiation and convection.

  • flexible (bending radius ≥ 7.5 x 10⁻³ m)
  • low thermal resistance
  • wide temperature range
  • fast response time
  • large guard area
  • integrated type T thermocouple
  • robustness, including wiring with strain relief block
  • IP protection class: IP67 (essential for outdoor application)
  • integrated thermal spreaders for low thermal conductivity dependence


FHF04 is a sensor for general-purpose heat flux measurement. It is thin, flexible and versatile. FHF04 measures heat flux through the object in which it is incorporated or on which it is mounted, in W/m2. The sensor in FHF04 is a thermopile. This thermopile measures the temperature difference across FHF04’s flexible body. A type T thermocouple is integrated as well. The thermopile and thermocouple are passive sensors; they do not require power.

Multiple small thermal spreaders, which form a conductive layer covering the sensor, help reduce the thermal conductivity dependence of the measurement. With its incorporated spreaders, the sensitivity of FHF04 is independent of its environment. Many competing sensors do not have thermal spreaders. The passive guard area around the sensor reduces measurement errors due to edge effects and is also used for mounting.

Using FHF04 is easy. It can be connected directly to commonly used data logging systems. The heat flux in W/m² is calculated by dividing the FHF04 output, a small voltage, by the sensitivity. The sensitivity is provided with FHF04 on its certificate. Equipped with a metal connection block, which may serve as strain relief, and with potted protective covers on both sides so that moisture does not penetrate, FHF04 has proven to be very robust and stable.

FHF04 calibration is traceable to international standards. The factory calibration method follows the recommended practice of ASTM C1130 – 17. When used under conditions that differ from the calibration reference conditions, the FHF04 sensitivity to heat flux may be different than stated on its certificate. See the user manual for suggested solutions. See also our application note how to install a heat flux sensor.

Would you like to to study energy transport / heat flux in detail? Hukseflux helps taking your measurement to the next level: order FHF04 with radiation-absorbing black and radiation-reflecting gold stickers. You can then measure convective + radiative flux with one, and convective flux only with the other. Subtract the 2 measurements and you have radiative flux. BLK – GLD stickers can be applied by the user to the sensor. Optionally, they can be ordered pre-applied. See the BLK – GLD sticker series user manual and installation video for instructions.

Suggested Use

FHF04 is a sensor for general-purpose heat flux measurement, often applied as part of a larger test- or measuring system. FHF04SC is a self-calibrating version of the standard model FHF04, combined with a heater. FHF04SC is used when the highest level of quality assurance is required and for long-term heat flux measurement. See the insightful video “FHF series explained” on our YouTube channel.


Building physics / insulation, thermal comfort and energy budget measurement
Heat flux measurement to validate CFD thermal simulations
Industrial monitoring and control / heat flux and heat transfer measurement
Meteorology / surface energy flux measurement
Scientific research / heat and heat transfer measurement


BLK – GLD stickers
Black and gold stickers for measuring convective and radiative heat flux separately
convective and / or radiative heat flux



heat flux, temperature

Measurement range

(-10 to +10) x 10³ W/m²

Sensitivity (nominal)

11 x 10⁻⁶ V/(W/m²)

Temperature sensor

type T thermocouple*

Thermal spreaders


Rated bending radius

≥ 7.5 x 10⁻³ m

Rated load on cable

≤ 1.6 kg

Outer dimensions foil with guard

(50 x 50) x 10⁻³ m

Sensor thermal resistance

11 x 10⁻⁴ K/(W/m²)

Sensor thickness

0.4 x 10⁻³ m

Uncertainty of calibration

± 5 % (k = 2)

Rated temperature range - continuous use

-70 to +120 °C

Rated temperature range - short intervals

-160 to +150 °C**

IP protection class


Standard wire length

2 m


with 5 m wire length; without wiring, without metal connection block; BLK-5050 black sticker; GLD-5050 gold sticker

* temperature measurement uncertainty: 2 % of value in ˚C. For details, refer to user manual

** when measuring at temperatures of -160 °C , contact Hukseflux.

*** sensor is not suitable for continuous exposure to water


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