Non-invasive thermal energy measurement at:

  • Heating systems (e.g. Boilers)
  • Refrigeration and air-conditioning systems
  • Refrigeration compressors (also in the gas phase)
  • Absorption chillers
  • District heating transport pipelines and transfer stations

Heat exchanger for industrial processes:

  • Efficiency monitoring on heat exchangers in line with preventative maintenance
  • Comparison of the amount of energy produced and primary energy used in boilers and burners
  • Permanent monitoring of energy flows
  • Quantification and use of residual heat
  • High temperature flow measurements of heat transfer oils or molten salts
Technical Datasheet
tsfluxus_fg721 - en-gb.pdf
Adobe Acrobat Document 1.1 MB

The FLUXUS F721 Energy is specially designed for heat and cold quantity metering within industrial environments and is thus also available as hazardous area approved variants(ATEX, IECEx Zone 2).

Like all measuring systems of the FLUXUS series, the F721 Energy measures the volumetric flow rate non-invasively via its clamp-on ultrasonic transducers. Simultaneously, temperature probes monitor the temperatures at the supply and return lines of the heating or cooling system - either non-invasively with clamp-on technology or by use of wetted temperature probes.
From the temperature difference as well as the measured volume flow rate and on the basis of the physical media parameters stored in the internal database of the transmitter, the heating or cooling performance is calculated. With the help of the built-in totalizer function the FLUXUS F721 Energy can also be used as an energy meter.

Further, the FLUXUS F721 Energy can also be equipped with two measurement channels to:
- allow for a complete energetic monitoring of a heat exchanger,
- to simultaneously measures at two heat- or cold carrying lines or
- to allow accurate measurements even at strongly disturbed flow profiles by compensating these.

Another important advantage of FLUXUS F721 Energy lies within its high zero point stability and unrivalled accuracy even at very low flow rates - signal drift and significant measurement uncertainty, as it can often be observed at magnetive-inductive heat quantity meters when measuring at low flow rates, can be ruled out. Moreover, even potential mineral deposits on the inner pipe wall cannot influence the measurement.

The range of applications of the F721 Energy is almost unlimited, not only in terms of pipe dimensions (from 6 mm up to 12.000 mm), pipe materials and their manufactured quality (e.g. badly manufactured GRP pipes or rusty steel pipes) and temperatures (from -190 ° C up to + 650 ° C) but also in terms of flowing media - from process and cooling water, to thermal oils or cryogenic media.

Both the ultrasonic transducers and temperature probes are carefully paired and matched by FLEXIM. Due to these processes, the system measures with a high degree of accuracy and repeatability - even in applications with only small temperature differences, such as in cooling water circuits. The clamp-on ultrasonic sensors are well protected in extremely robust stainless steel mounting fixtures and withstand even the harshest mechanical stresses.

Thus, the FLUXUS F721 Energy offers the best metrological basis in terms of precision, long-life time, maintenance-free as well as cost-effective monitoring of thermal energy flows within industrial environments and thus forms the foundation for further process optimization tasks within the scope of a holistic energy management system - e.g. according to DIN ISO 50001.


  • Reliable and wearfree measurement from outside
  • Virtually unlimited application range - even at extreme applications (from -190 °C uo to +650 °C)
  • Accurate thermal energy measurement due to:
    - highly accurate flow measurement with paired and traceable calibrated ultrasonic transducers
    - highly accurate temperature measurement with paired and traceable calibrated temperature sensors (acc. to DIN EN 1434-1)
  • Extremely high measuring dynamics from the lowest to the highest flow velocities - captures even the slightest flows at night time
  • Simple, cost-effective retrofitting without any disruption to supply
  • Tamper-proof storage of measuring data


Quantities of measurement

Heat Quantity, Volume Flow, Mass Flow, Flow Velocity


Any liquid media up to 10% of gaseous or solid entrainments

Media temperature

-40°C ... +200°C; (-190°C ... +650°C with WaveInjector mounting fixture)

Pipe diameter range

6 mm ... 12.000 mm (no limitations on wall thickness and material)

Flow velocity range

0,01 ... 25 m/s

Flow channels

1 or 2

Measurement accuracy

Flow: ±0.5 % of reading, ±0,01 m/s (without applicative disturbances)

Measurement accuracy


Temperature: ± 0,01% of reading, ± 0,03 K

Measurement accuracy


Flow: ±1.2 % of reading, ±0,01 m/s

Measurement accuracy

(field calibrated)

Flow: ±0.5 % of reading, ±0,01 m/s


Flow: ±0.15% of reading, ±0,01 m/s

Communication Protocol

Modbus RTU, HART, Foundation Fieldbus, Profibus PA, BACNet MS/TP or IP, M-Bus

Operating temperature of the transmitter

-40°C ... +60°C

Degree of protection

Transmitter: IP66, Transducers: up to IP68

Available Hazardous Area Classification (optional)

ATEX and IECEx Zone 2, Inmetro, EAC TR-TS

Inputs Energy Version

Max. 4, Temperature (Pt100/Pt1000), Current, Voltage, Binary

Outputs Energy Version

(Switchable active/passive) Current, Voltage, Frequency, Binary