A next-level sensor from the world market leader in heat flux measurement, FHF04SC is a combination of our standard model FHF04 heat flux sensor and a heater. The heater allows the user to perform self-tests, verifying sensor functionality and stability during use, without having to remove the sensor. FHF04SC is ideal for high-accuracy and long-term heat flux measurement, construction of calorimeters, (zero heat flux) core temperature measurement and thermal conductivity test equipment.

  • Flexible (bending radius ≥ 15 x 10⁻³ m)
  • Low thermal resistance
  • Wide temperature range
  • Fast response time
  • Integrated type T thermocouple
  • Robustness, including metal connection block, may be used as strain relief
  • IP protection class: IP67 (essential for outdoor application)
  • Integrated thermal spreaders for low thermal conductivity dependence


FHF04SC 1 self calibrating webv2101FHF04SC is a sensor for general-purpose heat flux measurement, combined with a heater. It is used when the highest level of quality assurance is required and for long-term heat flux measurement. It is thin, flexible and versatile. FHF04SC measures heat flux through the object in which it is incorporated or on which it is mounted, in W/m². The sensor in FHF04SC is a thermopile. This thermopile measures the temperature difference across FHF04SC’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 FHF04SC is independent of its environment. Many competing sensors do not have thermal spreaders. The passive guard area around the sensor reduces edge effects and is also used for mounting.

hfluxman FHF04 lab largesq printv2101

Using FHF04SC is easy. It can be connected directly to commonly used data logging systems. The heat flux in W/m² is calculated by dividing the FHF04SC output, a small voltage, by the sensitivity. The sensitivity is provided with FHF04SC on its product certificate. When used under conditions that differ from the calibration reference conditions, the FHF04SC sensitivity to heat flux may be different than stated on its certificate. See the user manual for suggested solutions.

FHF04SC 2 with heater webv2101Measuring heat flux, users may wish to regularly check their sensor performance. During use, the film heater is activated to perform a self-test. The heat flux sensor response to the self-test results in a verification of sensor performance.  Implicitly also cable connection, data acquisition, thermal connection of sensor to its environment and data processing are tested. Heat flux sensors are often kept installed for as long as possible. Using self-testing, the user no longer needs to take sensors to the laboratory to verify their stable performance. In a laboratory environment, using a metal heat sink, you may even perform a formal calibration. The heater has a well characterized and traceable surface area and electrical resistance.

fhf05 3upWould you like to study energy transport / heat flux in detail?  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:

  • high-accuracy scientific measurement of heat flux, with a high level of data quality assurance
  • study of convective heat transfer mechanisms
  • calorimeter prototyping
  • (zero heat flux) non-invasive core temperature measurement
  • thermal conductivity test equipment



  • 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 sticker series


Measurand 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 included
On-line functionality testing self-test including self-calibration
Rated bending radius ≥ 15 x 10⁻³ m
Rated load cable ≤ 1.6 kg
Outer dimensions foil with guard (50 x 50) x 10⁻³ m
Sensing area 9 x 10⁻⁴ m²
Sensor thermal resistance 30 x 10⁻⁴ K/(W/m²)
Sensor resistance range 160 to 240 Ω
Sensor thickness 0.7 x 10⁻³ m
Uncertainty of calibration ± 5 % (k = 2)
Rated temperature range – continuous use -40 to +120 oC**
IP protection class IP67***
Standard wire length 2 m
Heater resistance 100 Ω (nominal)
Heater power supply 12 VDC
Options with 5 m wire length; BLK-5050 black sticker; GLD-5050 gold sticker
* temperature measurement uncertainty: 2 % of value in C. For details, refer to user manual.
** rated operating conditions: 120 ˚C continuous use, 150 ˚C short intervals; use to -80 ˚C is possible.
*** sensor is not suitable for continuous exposure to water.

Frequently asked questions

How to measure heat flux?

Heat flux sensors measure energy flux onto or through a surface in [W/m²].
The source of the heat flux may be:

  • conduction
  • radiation
  • convection

Convective and conductive heat transfer are associated with a temperature difference. Heat always flows from a source to a sink, from a hot to a cold environment. Convective and conductive heat flux is measured by letting this heat flow through the sensor. Radiative flux is measured using heat flux sensors with black absorbers. The absorbers converts radiative to conductive energy. Hukseflux started in 1993 with sensors for measurement of heat flux in soils and on walls. In the course of the years, we have added specialised sensors and systems for many other applications.
Heat flux sensors manufactured by Hukseflux are optimised for the demands of different applications:

  • rated temperature range
  • rated heat flux range
  • sensitivity
  • response time
  • chemical resistance, safety requirements
  • size, shape and spectral properties

Hukseflux is the world market leader in heat flux measurement. We have prepared a white paper briefly explaining the fundamentals of measuring with heat flux sensors. It also offers general directions what to watch out for and some, perhaps surprising, applications of heat flux sensors. Take a look at our white papers.

What matters most when measuring with a heat flux sensor?

There are quite a few general considerations when starting a heat flux measurement.

  • Representativeness in time and space; average!
    A heat flux sensor measures at a certain location. Is this location representative of what you need to measure? If possible, use a relatively large sensor, rather than a small one, and consider use of multiple sensors. Thermal processes often have large time constants; instantaneous measurements may be misleading. Average to get the full picture.
  • Optical properties
    When heat flux sensors also measure radiation, pay attention to the surface color. If needed paint the sensor surface. Please mind that shiny metallic surfaces reflect both infra-red and visible radiation. Paints may have different colors in the visible range, but are usually “black” absorbers in the far-infra-red.
  • Sensor thermal resistance
    A heat flux sensor distorts the local heat flux. In order to minimize this effect, use the sensor with the lowest possible thermal resistance.
  • Edge effects
    A heat flux sensor locally distorts the heat flow pattern, in particular around the edges of the sensor. A passive guard, i.e. a non-sensitive part around the sensor is essential to avoid errors due to edge effects.

There are more characteristics that matter. Please find them in our white paper on heat flux fundamentals and applications.

Which sensor(s) to use for surface energy flux measurement?

Hukseflux manufactures a range of sensors for surface energy flux measurements. All have proven reliability.
These state-of-the-art sensors are made for the global fluxnet community:

  • NR01 is a market leading 4-component net radiometer.
  • HFP01 and HFP01SC measure soil heat flux.
  • STP01 offers an accurate temperature profile measurement.
  • TP01 is the leading sensor for soil thermal conductivity.

Sensors made by Hukseflux are designed for compatibility with most common datalogger models. For many models we have example programs and wiring diagrams available.

How to measure R-value and U-value of buildings?

On-site measurements of thermal resistance, R, are often applied in studies of buildings. Alternatives are to measure its inverse value, the thermal conductance which is called the Λ-value, or the thermal transmittance which includes ambient air boundary layer thermal resistance, the U-value. The measurements of R are based on simultaneous time averaged measurement of heat flux Φ and differential temperature, ΔT, (using two temperature sensors on each on a different side of the wall).

R = ΔT / Φ

Hukseflux provides a range of sensors and measuring systems for use in measurement of the energy budget of buildings and characterization of construction materials.

HFP01 heat flux sensor and TRSYS01 measuring system are widely used for on-site measurements on walls, windows and other construction elements in building physics.

  • HFP01 can be used for in-situ measurement of building envelope thermal resistance (R-value) and thermal transmittance (H-value) according to ISO 9869, ASTM C1046 and ASTM 1155 standards. HFP01 is the world’s most popular sensor for heat flux measurement in the soil as well as through walls and building envelopes. HFP01 measures heat flux through the object in which it is incorporated or on which it is mounted, in W/m². More information? Visit the HFP01 product page.
  • TRSYS01 is a high-accuracy system for on-site measurement of thermal resistance, R, thermal conductance, the Λ-value, and thermal transmittance, the U-value, of building envelopes. TRSYS01 is mostly used for measurements according to standard practices of ISO 9869 and ASTM C1155 / C1046. The system is equipped with high-accuracy electronics, two heat flux sensors of model HFP01 as well as two pairs of matched thermocouples. The two measurement locations provide redundancy, leading to a high level of confidence in the measurement result. The high accuracy of the heat flux sensors and temperature difference measurements ensures that TRSYS01 continues measuring when other systems no longer perform; in particular at very low temperature differences across the wall.

Where can I find complete heat flux measuring systems?

Hukseflux, market leader in heat flux measurement, offers both sensors and systems.

These measuring systems typically include a Measurement and Control Unit and one or more sensors for measuring heat flux as well as other measurands, such as temperature and humidity. Examples are the TCOMSYS01 Hot Cube thermal comfort measuring system, including a TCOM01 sensor, and the TRSYS01 measuring system, incorporating two HFP01 heat flux sensors and two pairs of matched thermocouples.

Cannot find what you are looking for? Please contact us.