About Us


As a manufacturer of thermal mass flow meters for domestic and global markets for over 25 years, Fox Thermal provides resourceful solutions for industrial process, oil & gas, wastewater, and biogas applications. With the rapidly expanding demand for process accuracy and efficiency, we take the time to help customers eliminate downtime and achieve their vision.

Make Downtime a Thing of the Past

From the beginning, Fox Thermal founder Brad Lesko was acutely aware of the challenges customers faced in keeping their production lines up and running—and optimized. He also had a passionate belief in the future of thermal flow measurement—and a big idea. An idea that could radically streamline the process.

In 1994, working out of a garage in Gilroy, Brad and George Anderson designed the first one-piece thermal mass flow meter and took the leap—moving to a larger facility and slowly adding new employees. Under the steady hand of Al Arreola, production increased to meet the sales demand that Rich Cada cultivated through a national and then global network of sales representatives.

Within the last ten years, sales took off with the introduction of the advanced Model FT3, and later, Fox Thermal's DDC-Sensor™ (direct digitally controlled sensor), a fully integrated communications package, and field-programmable gas composition changes —always staying true to our vision to make downtime a thing of the past for your business.

Core Values

Fox Thermal's core values are the beliefs that support our vision and guide our actions.

Responsive - Knowledgeable and empowered Fox team members move quickly in response to new and existing customer needs.

Curious - Asking the right questions always produces a deeper understanding of customer challenges. We nerd out.

Engaging - We take the time. We work closely with customers to empower them to achieve their vision.

Resourceful - Like a clever fox, we find innovative and efficient paths to great customer outcomes.

Adaptable - Understanding that no two applications are alike, we help customers find their ideal solution because the magic is always in the service.


Fox Thermal Joins the Tasi Group of Companies

In April of 2019, Fox Thermal was acquired by Tasi Group located in Marlborough, Massachusetts. Given Tasi’s philosophy of acquiring great companies and supporting their expansion into new and growing market niches, Tasi is currently engaged in helping to strengthen the Fox Thermal brand through global marketing and sales.

The TASI Group is a globally-diversified company comprised of four strategic business segments that provide flow meter and flow control products as well as advanced test, measurement, inspection and assembly solutions that improve manufacturing processes and deliver value-added results. Using the latest electronics and software supported by experienced engineering teams, they meet equipment and manufacturing challenges that enable global customers to achieve the highest quality and reliability in their production environments.

Tasi solutions range from IIoT enabled products such as industrial wireless and real-time process monitoring, to leak test instrumentation and systems, bottle and can inspection, automated assembly lines, and the latest flow measurement technologies.

Explore other brands in the TASI Flow Group:

Air Monitor

Air Monitor has been delivering airflow measurement solutions since 1967 – 50 years! We are the premier solutions provider for the Commercial HVAC, Industrial Process, and Power Generation markets. We are the only dedicated airflow solutions provider with expertise in differential pressure and thermal dispersion measurement technologies.

AW-Lake Company

AW-Lake Company manufactures inline, positive displacement, mass Coriolis, variable area and turbine flow meters with an impressive array of electronic output and control options including; electronic sensors, inline optical sensors, flow switches/alarms and transmitters. The company’s flow monitoring products can be found in a broad array of market applications in the oil & gas, transportation, industrial, process, sanitary and medical/life sciences market segments.

Exact Dispensing Systems

Since 1978, Exact Dispensing Systems have designed and manufactured high quality equipment for the dispensing of single component fluids and plural component reactive resins such as epoxies, urethanes and silicones. Their materials and application expertise helps clients make the best decisions regarding their specific dispensing application. The EXACT staff members always take the time to understand the customer’s process requirements and then develop a valid, sensible, cost-effective dispensing solution to meet those needs.

KEM Küppers Elektromechanik GmbH

With more than 50 years of experience, complemented by innovative and customer-specific product development, KEM Küppers Elektromechanik GmbH is an expert in flow measuring technology and calibration. KEM is an independent, vertically integrated manufacturer that designs and produces standard and customized mechanical or static flow meter solutions.

Litre Meter

Litre Meter has been manufacturing flow meters since 1975 and positive displacement flow meters since 1986. This reservoir of knowledge is used to expertly select the appropriate meter technology and provide effective flow measurement solutions. Main markets are chemical injection and hydraulic applications in the Oil & Gas sector worldwide.


ONICON Incorporated has been delivering market leading flow and energy measurement products since 1987. For more than 30 years we have been exclusively focused on delivering quality engineered flow and energy measurement instruments for hydronic heating and cooling systems. Our broad range of product solutions are wet-calibrated, fully programmed for your application, and ready to use right out of the box.

Pulsar Measurement

Delivering the Measure of Possibility, Pulsar Measurement is a world-leading manufacturer and supplier of flow, level, sludge interface measurement, and pump control instrumentation. Technologies include clamp-on transit time and doppler ultrasonic for flow measurement in full pipes, contacting and non-contacting solutions for area-velocity for flow measurement in partially filled pipes and channels, and continuous level measurement via ultrasonic or frequency modulated continuous wave radar.


Seametrics, an ONICON Measurement Solutions business, is a designer and manufacturer of a wide variety of flow metering and submersible sensor products. Since 1990 we have provided innovative solutions to users in irrigation, fracking, water treatment, groundwater, surface water, and chemical processing applications. Our products have a reputation for durability and accuracy at a competitive price, and are sold through a network of domestic and international distributors.


SignalFire’s unique Open Architecture Wireless Mesh Network permits users to create wireless sensor networks using the sensors and actuators best suited for the job rather than the a wireless option provided by a sensor vendor. SignalFire’s intrinsically safe battery powered nodes can power both the attached sensors and the wireless system making the system truly wireless.

Vögtlin Instruments GmbH

Vögtlin Instruments GmbH is a Swiss designer of gas flow measurement and control instruments. Vögtlin has over 25 years of experience in designing and manufacturing high precision thermal mass flow meters and controllers, variable area flow meters and control valves. The core competence on calibration and OEM solutions together with the aplication expertise throughout its worldwide sales partner network make Vögtlin a strongly respected player in various industrial fields such as medical, biotechnology, surface treatment, coating & hardening and new energy.

Our Technology - How it Works

Thermal Mass Flow Technology

All thermal Gas Mass Flow Meters from Fox utilize the thermal sensing principle, a proven, accurate direct mass flow measurement technology. This technology performs at high levels of accuracy for a wide variety of gases.

Fox Thermal Flow Meters use a constant temperature differential (constant Δ T) technology to measure mass flow rate of air and gases. Fox Models FT2A and FT3 are equipped with the PowerPro™ Sensor while Models FT1, FT4A & FT4X have the DDC-Sensor™. Both thermal mass flow sensors consist of two Resistance Temperature Detectors (RTD’s). The sensor elements are constructed of a reference grade platinum wire wound around ceramic mandrels that are inserted into stainless steel tubes.

Benefits of Thermal Mass Flow Measurement

There are many benefits of thermal gas mass flow meters over other flow measurement technologies and Fox Thermal leads the industry for accuracy, quality, and innovative design. Benefits of Thermal Mass Flow Technology:

  • Direct mass flow measurement of air and gases in standard volumetric units (e.g., SCFM or NM3/H) or mass units (e.g., LBS/M or KG/H)
  • No additional pressure or temperature compensation required
  • Repeatability and exceptionally broad measurement range: up to 1000:1 (100:1 typical)
  • Standard linear 4-20mA output proportional to mass flow rate
  • Low pressure drop
  • No moving parts
  • Cost-effective
  • Insertion, Inline & remote* styles
  • Measures flow rate and temperature

The Digital Difference


Fox Thermal is the leader in thermal mass flow measurement because it brings the Digital Difference. Fox Thermal is the only thermal mass flow manufacturer with digital sensor technology. It's like no other flow sensor available on the market today. Instead of using analog circuitry, Fox Thermal's DDC-Sensor™ (Direct Digitally Controlled Sensor) is interfaced directly to the meter's microprocessor for more speed and programmability. This revolutionary advancement in the technology has laid the foundation for award-winning and truly innovative flow meter features.

The 3rd generation of Fox's DDC-Sensor™ is a state-of-the-art sensor technology used exclusively in Models FT1, FT4A, & FT4X Thermal Gas Flow Meters. Fox’s unique DDC-Sensor™ provides a technology platform for calculating accurate gas correlations. The correlation algorithms allow the meter to be calibrated on a single gas in the factory while providing the user the ability to select other gases in the Gas-SelectX® gas menu(s).

Competitors' sensors utilize fragile, cantilevered (only welded at one end) elements, whereas the sensor elements of the DDC-Sensor™ are welded to the sensor window at both ends for extra stability and strength. This enhanced design eliminates the sensor element vibration - found most often at high flow rates - which can potentially lead to metal fatigue and failure.

The sensor elements are in direct contact with the process flow. In applications where slag, ice, or other foreign particles are traveling down the pipe, cantilevered elements are subject to damage requiring factory repair. The Fox 3rd generation non-cantilevered sensor design is more rugged and robust.

Fox Models FT1, FT4A, & FT4X, with their DDC-Sensor™ and state-of-the-art correlation algorithms provide an accurate, multi-gas-capable thermal gas flow meter. For more information on the capabilities of the DDC-Sensor™ technology, read this Sensor Tech Tip document to gain a better understanding of the advanced sensor design and function.


Fox Thermal is the leader in thermal mass flow measurement because it brings the Digital Difference. The digital sensor design has laid the foundation for the development of advanced product features like the CAL-V™ Calibration Validation feature.

Fox Thermal’s CAL-V™ Calibration Validation feature allows the user to run a test in the field and at the push of a button. There is no need for other equipment, gas canisters, or process downtime. The test can be run under normal process conditions with gas flowing in the pipe!

The CAL-V™ test does the following:

  • Tests the functionality of the sensor and its associated signal processing circuitry
  • Ensures that the meter still retains its original NIST-traceable calibration
  • Checks for build-up on sensor that could affect calibration

Fox Models FT1, FT4A & FT4X, with their DDC-Sensor™ and state-of-the-art correlation algorithms provide an accurate, multi-gas-capable thermal gas flow meter.


Fox Thermal is the leader in thermal mass flow measurement because it brings the Digital Difference. The digital sensor design has laid the foundation for the development of advanced product features like the Gas-SelectX®; Gas Selection Menus feature.

In some applications, like Biogas measurement or natural gas flow measurement, the gas composition may vary over time. Flow meters must be calibrated to the gas composition specific to the application in order to accurately measure the flow of the gas. If that gas composition changes, the calibration uncertainty will be affected and the flow meter will not measure as accurately as specified. To combat this challenge, Fox Thermal’s Gas-SelectX® feature allows the user to set a new gas composition in the meter's electronics in the field and at the push of a button. There is no need for auxiliary equipment, to send the meter back for re-calibration, or for process downtime. The change can be made at any time and can be performed as many times as desired and under normal process conditions - with gas flowing in the pipe!

Gas-SelectX® offers an extensive selection of pure gases to choose from along with the ability to mix percentages of gases for a custom gas mix.

Fox Models FT1, FT4A & FT4X, with their DDC-Sensor™ and state-of-the-art correlation algorithms provide an accurate, multi-gas-capable thermal gas flow meter.

View and read the Gas-SelectX® Datasheet for more information.

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Asking the right questions
for over 25 years.