Thermal Actuator Types and Their Benefits in Our Lives

Thermal actuators have now become part of many equipment or machines that require motion energy. Various thermal actuator types become mechanical systems that can create motion according to the expansion and contraction of materials. These materials use a thermal induction process.

We can easily find various types of thermal actuators in applications from devices that use small footprint, high force output, and low voltage. All types of thermal actuators have piston components and also contain thermal sensitive materials such as wax.

This wax material will expand as the temperature increases. It is in proper calculation so that it can push the piston out of the actuator. Then when the thermal actuator encounters a decrease in temperature, the thermal sensitive material will contract. The piston will return to its initial position. The combination of all its components produces linear movement. This is a form of response to changes in temperature inside it.

These non-electric motors are an important part of the automotive, agricultural, aerospace and many other industries. Most wax-based thermal actuators rely on thermal expansion rather than complex motorized drives. They just rely on changes in temperature to be able to do what the system needs. Some of the system’s work include opening or closing valves, releasing latches, operating switches, and many more.

Thermal Actuator Types by Function (Most Common Classification)

In practical applications and market usage, thermal actuator types are most commonly classified based on how they operate and how they are controlled.

ON/OFF Wax Thermal Actuators

ON/OFF wax thermal actuators are the most widely used type. They operate in a simple open‑or‑close manner. When the temperature or electrical heating element reaches a specific level, the wax expands and drives the piston to its working position. When the temperature drops, the actuator returns to its original position with the help of an internal or external spring.

This type is commonly used in underfloor heating systems, radiator valves, fan coil units, and hydronic HVAC applications where precise modulation is not required.

Proportional Thermal Actuators

Proportional thermal actuators are designed to provide gradual or proportional movement instead of simple ON/OFF action. The actuator stroke varies according to the control signal, typically 0–10 V or similar analog control.

This type is suitable for advanced HVAC systems that require better temperature regulation, energy efficiency, and smoother valve control.

Smart Thermal Actuators

Smart thermal actuators integrate wireless or digital control technologies such as Wi‑Fi, Zigbee, or Tuya systems. While the internal working principle remains based on thermal expansion, the control and communication are handled through smart controllers or building management systems.

These actuators are commonly used in smart homes and modern commercial buildings.

Comparison Table: Thermal Actuator Types by Function

Type	Control Method	Movement Style	Typical Applications
ON/OFF Wax Thermal Actuator	Fixed ON/OFF	Linear, fixed stroke	Underfloor heating, radiator valves
Proportional Thermal Actuator	0–10 V / analog	Variable, proportional	Advanced HVAC, energy‑efficient systems
Smart Thermal Actuator	Wireless / digital	ON/OFF or proportional	Smart homes, BMS systems

Thermal Actuator Types by Internal Mechanism (Engineering Classification)

From an engineering and design perspective, thermal actuators can also be classified according to their internal construction.

Pusher Thermal Actuator

The pusher thermal actuator is a type that does not use a diaphragm or elastomeric bag. It delivers relatively high pushing force because there is no flexible membrane limiting movement. The main components include wax material, a piston, a vessel, and sealing elements.

Because there is no elastomer bag to contain the melted wax, this type requires very precise sealing and manufacturing accuracy. Any leakage may directly affect performance and reliability.

Flat Diaphragm Thermal Actuator

This is one of the commonly used thermal actuator designs in general applications. The diaphragm has controlled deformability and returns to its original shape when external force is removed. Among common designs, the flat diaphragm type usually has a shorter output stroke, typically around 3–4 mm.

In this design, the piston is positioned above the diaphragm, which requires a longer piston guide for stable movement. When the temperature rises, the wax expands and pushes against the diaphragm. The diaphragm transfers this force to the piston. When the temperature decreases, an external spring helps return the piston to its original position.

This type is suitable for applications that do not require long stroke lengths but demand stable and repeatable operation.

Press‑On Thermal Actuator

Press‑on thermal actuators use an elastomeric bag to contain the wax material. The piston is surrounded by wax inside this flexible bag. When the wax expands due to heat, the elastomer bag presses against the piston and generates movement.

This design allows for a more compact structure and often supports longer stroke lengths compared to flat diaphragm types. An external spring is usually required to reset the actuator once the temperature decreases.

Comparison Table: Thermal Actuator Types by Internal Mechanism

Mechanism Type	Stroke Length	Force Capability	Structural Characteristics
Pusher Type	Medium	High	No diaphragm, high sealing accuracy required
Flat Diaphragm Type	Short (≈3–4 mm)	Medium	Stable, widely used, simple structure
Press‑On Type	Medium to long	Medium to high	Compact, elastomer bag design

Relationship Between Functional and Mechanical Types

In real products, functional types and internal mechanisms are closely related. A smart or proportional thermal actuator may internally use a flat diaphragm or press‑on structure. Therefore, classification by function helps users choose the right product, while classification by internal mechanism helps engineers understand design and performance characteristics.

Which Thermal Actuator Type Should You Use?

When selecting a thermal actuator, users do not need to choose based on the internal mechanical structure of the actuator. Internal designs such as diaphragm or wax capsule forms are determined by the manufacturer and do not affect installation compatibility or system operation in most HVAC applications.

Selection should instead be based on functional and application requirements, including control method (ON/OFF, proportional, or smart control), operating voltage, normally open or normally closed behavior, stroke length, output force, valve connection size, and the intended working environment. By focusing on these parameters, users can reliably select the appropriate thermal actuator for their system without needing to consider internal construction details.

Product Classification by Thermal Actuator Type (Legom Products)

Based on functional classification, the following table shows how Legom thermal actuator products are categorized according to control method and application.

Thermal Actuator Manufacturing Process

To better understand how thermal actuators are built and how their internal components work together, the following video shows the manufacturing process of a typical wax-based thermal actuator. The example shown is the LEGOM 920062 thermal actuator, which represents a common design used in HVAC valve control applications.

Note: The video is provided for reference to illustrate general manufacturing and assembly processes. Internal structures and processes may vary between models and configurations.

Product Introduction Example: 920062PL Thermal Actuator

To provide a clearer understanding of how a finished thermal actuator is applied in real HVAC systems, the following video introduces the LEGOM 920062PL thermal actuator. The video highlights the product’s design, intended applications, and role in precise temperature control for heating and valve systems.

Conclusion

Thermal actuator types are best understood through their functional behavior and application requirements rather than internal mechanical construction. By focusing on control method, operating voltage, valve compatibility, stroke, and intended use, users can select suitable thermal actuators with confidence. Combining clear functional classification with practical examples and product references helps simplify decision-making while supporting reliable system performance in HVAC and related applications.

Last reviewed: January 2026