HFS01 is a water-cooled sensor that measures high-level radiative and convective heat fluxes. It is designed for studies of concentrated solar irradiance (800 x concentrated direct solar radiation) and high-intensity flames (gas burners, coal fires). HFS01 has a very robust all-metal / ceramics instrument body and sensor, and is equipped with a high-temperature cable to survive the extreme conditions of a typical experiment.

  • Robust all-stainless steel body
  • High-temperature signal cable
  • Signal wires electrically insulated from the sensor body and from cooling water



Measurand heat flux, temperature
Measurement range 0 to 800 x 10³ W/m²
Measurand in SI units heat flux density /irradiance in W/m²
Heat flux sensor thermopile
Temperature sensor thermocouple type K
Sensitivity (nominal) 9 x 10⁻⁹ V/(W/m²)
Calibration traceability to SI units
Rated operating temperature ranges :
sensor and black coating -30 to +650 °C
IP protection class IP67
Standard cable lengths :
high-temperature cable 1 m (see options)
low-temperature extension cable 3 m (see options)
Rated cooling water temperature range 10 to 30 °C
Rated cooling water flow > 30 l/h (0.01 l/s), preferably 100 l/h (0.03 l/s)
Output signal DC voltage
Output signal range 10 x 10⁻³ V at rated measurement range
Spectral range 0 to 50 x 10⁻⁶ m
Full field of view angle 180 °
Black coating emissivity 0.92 (estimate)
Order code HFS01 – high-temperature cable length in m – low-temperature extension cable length in m
Options • Longer cable (specify total cable length for both cable types in m)
• Connector at HFS01 cable end
• Low-temperature extension cable with 2 connectors, matching cable connector and chassis connector
• Chassis connector with internal wiring (colour code of wiring identical to cable colour code)
• Blank metal sensor surface, no coating


HFS01 1 webv1902HFS01 measures heat flux in the range of (0 to 800) x 10³ W/m²; the extremely high fluxes as generated by flames and solar concentrators.

Equipped with a black absorber, the instrument is designed for measurement in an environment in which heat flux includes radiation as well as convection. HFS01’s thermopile sensor generates an output voltage proportional to the total absorbed heat flux. The sensor must be water-cooled. Water cooling is usually supplied by tap water. A removable flange that can be used for mounting is supplied with the sensor. Also, a type K thermocouple is included, to measure the sensor body temperature.

HFS01 6 webv1901The part of the cabling closest to the sensor is a special high-temperature metal sheathed cable with an interlocked spiral stainless steel armour. The high-temperature cable and armour withstand temperatures up to 900 °C. Because the sensor body is water cooled, it will remain relatively cool. The surface temperature of the sensor may reach 650 ˚C. The low-temperature extension cable has a jacket of PTFE type plastic.

The HFS01 sensor can also be ordered without black coating, so that HFS01’s absorption of radiation is reduced, while it remains sensitive to convective radiation. Users may also coat HFS01 with their own coating, to create a different response to radiation.

HFS01 5 water cooled sensor webXLv1901HFS01 has Several Advantages:

      • Very robust all-metal / ceramics instrument body and sensor
  • High-temperature signal cable
  • Signal wires electrically insulated from the sensor body and from cooling waterhfluxman HFS01 02 solar concentrator fluxes webXLsquarev1901Using HFS01 is easy. It can be connected directly to commonly used data logging systems. The heat flux, in W/m², is calculated by dividing the HFS01 output, a small voltage, by the sensitivity. The sensitivity is provided with HFS01 on its product certificate. Equipped with heavy-duty cabling and a fully stainless steel casing which prevents moisture from penetrating the sensor, HFS01 has proven to be very reliable.

HFS01 calibration is traceable to international standards. The factory calibration method follows the recommended practice of ASTM C1130-07 (2012).

Suggested Use

  • Solar concentrator
  • Flame research
  • Fluidised beds

Areas of Application

  • Building physics / insulation, thermal comfort and energy budget measurement
  • Industrial monitoring and control / heat flux and heat transfer measurement
  • Scientific research / heat and heat transfer measurement

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.