Thermocouple VS Thermopile in Gas Equipment Applications

By Michael Angello – Parts Sales Manager

Thermocouples and thermopiles are critical gas safety devices used in many pieces of gas-heated restaurant equipment. How do they work, why do we use two different safeties, are they interchangeable, and what are their differences, is important information to know about these restaurant equipment parts.  These are the questions that have been asked many times, this blog describes their purpose and how they are used in your commercial cooking equipment.

Firstly, it is important to understand the critical nature of thermocouples and thermopiles. They are effectively a safety switch that ensures your gas shuts off if the pilot light is not lit, therefore it prevents unlit gas from filling your kitchen. Both thermocouples and thermopiles operate by making a thermoelectric connection. They take the heat from a flame and convert it to a very small electrical output using dissimilar metals.  The thermocouple will generate around 30 millivolts and the thermopile will generate around 300 millivolts.  If these numbers look somewhat similar that is because the thermopile is usually around 10 thermocouples tied together most of the time in series but can also be found in parallel.  The flame being used is generally a pilot light.  The thermocouple will be immersed in the flame and the thermopile will be heated at the tip.

In the realm of commercial kitchen equipment, precise temperature control is crucial for both safety and performance. Two key components that play a vital role in temperature measurement and control are thermocouples and thermopiles. While they serve similar purposes, their construction, functionality, and applications differ significantly.

This article explores the differences between these two commercial kitchen equipment parts and provides insight into whether these components can be used interchangeably.

What Is a Thermocouple?

A thermocouple is a temperature sensor that generates a voltage when exposed to a temperature difference between two junctions. It is made up of two dissimilar metals joined together at two points. When one junction is heated, the resulting voltage can be measured and translated into a temperature reading. Thermocouples are widely used in various applications such as gas heaters, furnaces, water heaters, and other appliances. They are particularly valuable in ensuring the safe operation of these devices by preventing overheating and monitoring combustion chamber temperatures.

A thermocouple provides a constant output voltage when immersed in heat. That small electric current is used to hold open an electromagnet, which does not need a large amount to keep it open.  The thermocouple controls the flow of gas but is not opening the gas valve itself.  When heated gas begins to flow, you will still need a 24-volt circuit to operate the gas valve.

Applications of Thermocouples

• HVAC Systems: Measuring room or building temperatures to control heating and cooling systems.
• Safety Sensors: Detecting pilot light status in gas-fired heating systems to prevent gas leaks.
• Furnaces & Boilers: Monitoring combustion chamber temperatures to prevent overheating.
• Water Heaters: Maintaining consistent water temperatures and ensuring safe operation.

What Is a Thermopile?

A thermopile is an assembly of several thermocouples connected in series to enhance the voltage output. This design allows thermopiles to measure temperature changes more accurately over a broader range. Thermopiles are commonly used in applications requiring non-contact temperature measurements, such as infrared thermometers and thermal imaging cameras. In gas fireplaces, thermopiles generate the voltage needed to operate the gas valves, ensuring a steady flame and consistent heating.

When a thermopile is used the voltage can vary but when heated directly in the flame the voltage becomes constant.  There is enough voltage on this to operate a gas valve and physically open the gas valve, so there is no need for a separate power source to open the valve.  Each one has its own type of uses designed by the manufacturer.

Applications of Thermopiles

• Gas Fireplaces: Generating the necessary voltage to maintain a stable flame and control gas flow.
• Clothes Dryers: Detecting when clothes are dry to save energy.
• Infrared Thermometers: Measuring temperature without direct contact by detecting thermal radiation.
• Thermal Imaging Cameras: Identifying temperature distribution across surfaces to spot insulation issues or air leaks.

Differences Between Thermopiles & Thermocouples

The primary differences between thermopiles and thermocouples are their construction, sensitivity, and voltage output. Thermocouples consist of a single pair of dissimilar metals and are typically used for direct temperature measurement and safety controls. In contrast, thermopiles are made up of multiple thermocouples connected in a series, resulting in higher sensitivity and voltage output. This makes thermopiles suitable for applications requiring more precise temperature measurements and the ability to generate sufficient voltage for device operation.

Finally, what are their differences and are they interchangeable?  They are not interchangeable with each other although they are similar, they do two different things in gas-fired systems.  Thermocouples are interchangeable with themselves; they are all the same construction but can be manufactured in different lengths.  We still suggest replacing it with the OEM-manufactured part but if it is not readily available anyone with the correct length will work.  Thermocouples are generally skinny and pointed at the top with a copper tube ending in a threaded connector.  Thermopiles are generally wider and will have actual wires leading off the body to screw onto terminals.  Thermopiles are also interchangeable with other thermopiles.

One last thing to be aware of is the cost of these items, while a Thermocouple will usually be less than $50 a Thermopile could be $50 and higher.

Conclusion

In the world of commercial kitchen equipment parts, understanding the roles and differences between thermocouples and thermopiles is essential for maintaining and repairing appliances. While both devices are crucial for temperature measurement and control, their specific applications and capabilities vary. Thermocouples are primarily used for direct temperature measurement and safety controls, whereas thermopiles are preferred for applications requiring higher sensitivity and voltage output. Ensuring the correct component is used for replacement is vital to maintaining the safety and functionality of your commercial kitchen equipment.

If you still cannot tell if you have a thermocouple or a thermopile, feel free to give our General Parts Group parts department a call at 1-888-498-1238 and one of our parts specialists will lend a hand.