Frost protection thermostats

Our THERMASREG® frost protection thermostats/frost protection monitors are used to monitor air conditioning systems, heat exchangers and heating registers and reliably protect against frost damage.

Guide to Antifreeze Thermostats

°C
Frost protection thermostat

THERMASREG® FST-8D

1102-1024-0102-000
Temperature monitors (self-switching)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3,6 ± 1,8 °F)
Capillary tube length: 0,6 m
Sensor response length: approx. 40 cm
Sensor: Copper
Permissible medium: Air
IP65
93,76 €

plus 19% VAT. + shipping

incl. VAT: 111,43 €
°C
Frost protection thermostat

THERMASREG® FST-5D

1102-1022-0102-000
Temperature controller (self-switching)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3,6 ± 1,8 °F)
Capillary tube length: 3.0 m
Sensor response length: approx. 40 cm
Sensor: copper
Permissible medium: air
IP65
96,34 €

plus 19% VAT. + shipping

incl. VAT: 114,58 €
°C
Frost protection thermostat

THERMASREG® FST-1D

1102-1021-0102-000
Temperature switches (self-switching)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3,6 ± 1,8 °F)
Capillary tube length: 6.0 m
Sensing response length: approx. 40 cm
Sensor: Copper
Permitted medium: Air
IP65
99,03 €

plus 19% VAT. + shipping

incl. VAT: 117,84 €
°C
Frost protection thermostat

THERMASREG® FST-3D
Temperature controllers (independently switching)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching output:
10 (2) A, AC 250 V;
due to the gold-plated contacts, also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3.6 ± 1.8 °F)
Capillary tube length: 1.8 m
Sensing response length: approx. 40 cm
Sensor: Copper
Permissible medium: Air / Water
IP65
101,05 €

plus 19% VAT. + shipping

incl. VAT: 120,24 €
°C
Frost protection thermostat

THERMASREG® FST-8D-HR

1102-1024-1102-000
Temperature limiter (with manual reset)
−10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3.6 ± 1.8 °F)
Capillary tube length: 0.6 m
Sensing response length: approx. 40 cm
Sensor: copper
Permissible medium: air
IP65
111,11 €

plus 19% VAT. + shipping

incl. VAT: 132,20 €
°C
Frost protection thermostat

THERMASREG® FST-5D-HR

1102-1022-1102-000
Temperature limiter (with manual reset)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
because of the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3,6 ± 1,8 °F)
Capillary tube length: 3.0 m
Sensor response length: approx. 40 cm
Sensor: copper
Permissible medium: air
IP65
118,56 €

plus 19% VAT. + shipping

incl. VAT: 140,98 €
°C
Frost protection thermostat

THERMASREG® FST-1D-HR

1102-1021-1102-000
Temperature limit switch (with manual reset)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3.6 ± 1.8 °F)
Capillary tube length: 6.0 m
Sensor response length: approx. 40 cm
Sensor: copper
Permissible medium: air
IP65
118,98 €

plus 19% VAT. + shipping

incl. VAT: 141,40 €
°C
Frost protection thermostat

THERMASREG® FST-3D-HR

1102-1023-1102-000
Temperature limiters (with manual reset)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts, also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3,6 ± 1,8 °F)
Capillary tube length: 1.8 m
Sensing response length: approx. 40 cm
Sensor: copper
Permissible medium: air / water
IP65
121,94 €

plus 19% VAT. + shipping

incl. VAT: 144,93 €
°C
Duct frost protection thermostat

THERMASREG® FST-K

1102-1064-0100-001
Temperature controllers (independently switching)
−10...+15 °C / +14...+59 °F,
factory setting w = +5 °C (+41 °F)
2 ± 1 K (3.6 ± 1.8 °F)
Changeover contact
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Protective tube:
made of metal, material CuZn37 (2.0321),
Ø 14 mm, NL = 205 mm
IP65
136,50 €

plus 19% VAT. + shipping

incl. VAT: 162,34 €
°C
Duct frost protection thermostat

THERMASREG® FST-K HR

1102-1064-1100-000
Temperature limiter (with manual reset)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
2 ± 1 K (3.6 ± 1.8 °F)
Changeover switch
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Protective tube:
made of metal, material CuZn37 (2.0321),
Ø 14 mm, L = 205 mm
IP65
153,87 €

plus 19% VAT. + shipping

incl. VAT: 182,94 €
°C
Frost protection thermostat

THERMASREG® FST-7D

1102-1025-0102-000
Temperature controllers (independently switching)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
also for switching of signal voltages < 24 V due to the gold-plated contacts
Switching differential: 2 ± 1 K (3.6 ± 1.8 °F)
Capillary tube length: 12.0 m
Sensor response length: approx. 40 cm
Sensor: Copper
Permissible medium: Air
IP65
170,72 €

plus 19% VAT. + shipping

incl. VAT: 203,02 €
°C
Frost protection thermostat

THERMASREG® FST-7D-HR

1102-1025-1102-000
Temperature limiter (with manual reset)
–10...+15 °C/ +14...+59 °F,
factory setting w = +5 °C (+41 °F)
Switching capacity:
10 (2) A, AC 250 V;
due to the gold-plated contacts also
switching of signal voltages < 24 V
Switching differential: 2 ± 1 K (3,6 ± 1,8 °F)
Capillary tube length: 12.0 m
Sensing response length: approx. 40 cm
Sensor: Copper
Permissible medium: Air
IP65
188,09 €

plus 19% VAT. + shipping

incl. VAT: 223,81 €
°C
2-phase frost protection thermostat

THERMASREG® FS20-UW 3m LCD

1102-1012-2102-030
0...+15 °C
typically ±1 K (at +10 °C)
1 x 0 -10 V control input DDC
1 x 0 -10 V cascade input
1 x 0 -10 V temperature output (corresponds to 0...+15 °C)
1 x 0 -10 V valve output
(frost signal with control voltage and cascade)
1 x volt-free changeover contact (24 V), setpoint range 0...+15 °C
Hysteresis of switching stage: 2K
Capillary tube length: 3.0 m
IP65
290,95 €

plus 19% VAT. + shipping

incl. VAT: 346,05 €
°C
2-phase frost protection thermostat

THERMASREG® FS20-UW-HE 3m LCD
0...+15 °C
typ. ± 1 K (at +10 °C)
1 x 0 -10 V control input for DDC
1 x 0 -10 V cascade input
1 x 0 -10 V temperature output (corresponds to 0...+15 °C)
1 x 0 -10 V valve output
(frost signal with control voltage and cascade)
1 x volt-free changeover contact (24 V), setting range 0...+15 °C
Hysteresis of the switching stage: 2K
Capillary tube length: 3.0 m
IP65
316,64 €

plus 19% VAT. + shipping

incl. VAT: 376,68 €
°C
2-phase frost protection thermostat

THERMASREG® FS20-UW 6m LCD

1102-1011-2102-030
0...+15 °C
typically ± 1 K (at +10 °C)
1 x 0 -10 V control input DDC
1 x 0 -10 V cascade input
1 x 0 -10 V temperature output (corresponds to 0...+15 °C)
1 x 0 -10 V valve output
(frost signal with control voltage and cascade connection)
1 x volt-free changeover contact (24 V), setpoint range 0...+15 °C
Hysteresis of the switching stage: 2K
Capillary tube length: 6.0 m
IP65
341,80 €

plus 19% VAT. + shipping

incl. VAT: 406,59 €
°C
2-phase frost protection thermostat

THERMASREG® FS20-UW-HE 6m LCD
0...+15 °C
typical ± 1 K (at +10 °C)
1 x 0 -10 V control input DDC
1 x 0 -10 V cascade input
1 x 0 -10 V temperature output (corresponds to 0...+15 °C)
1 x 0 -10 V valve output
(frost signal with control voltage and cascading)
1 x volt-free changeover contact (24 V), setpoint range 0...+15 °C
Hysteresis of the switching stage: 2K
Capillary tube length: 6.0 m
IP65
368,74 €

plus 19% VAT. + shipping

incl. VAT: 438,66 €

Antifreeze Monitors and Antifreeze Thermostats for Ventilation Systems

A freeze protection thermostat monitors the temperature in areas of a system that are at risk of freezing. If the temperature falls below the set threshold, the device provides a switching or control signal for the intended protective function. In ventilation and air-conditioning technology, such a device is often referred to as a frost protection monitor.

Depending on the model, the THERMASREG® versions in this collection are suitable for monitoring heat exchangers, water circulation systems, and heating coils. Options include mechanical temperature monitors, models with manual reset, duct-mounted versions, and electronic freeze protection solutions.

How does a freeze protection monitor work? Select the appropriate model Here's what you should look for when choosing a freeze protection monitor Selecting the Right Capillary Tube and Sensor Select a freeze protection thermostat that is compatible with the system Frequently Asked Questions About Frost Protection Thermostats and Frost Protection Monitors

Frost protection thermostat or frost protection switch: what is the difference?

In the context of ventilation, air conditioning, and heating systems, both terms are often used for the same protective purpose. Frost protection thermostat describes the temperature-dependent switching device. Frost protection monitor emphasizes its function: It monitors an endangered system area and reports frost danger to the system control.

For product selection, therefore, the technical design is less decisive than the designation. Relevant factors include the type of temperature monitor, the reset, the length and design of the sensor, the required output, and the conditions at the installation site.

How does a freeze protection monitor work?

The freeze protection switch measures the temperature via its sensor. In the mechanical THERMASREG® FST models, a capillary tube-diaphragm system performs this task. If the detected temperature drops below the set switching point, the electrical contact changes. This signal can be used by the system control to trigger the planned frost protection response.

Depending on the model, the system reverts automatically or only after manual unlocking. Electronic models may also feature analog inputs and outputs as well as a display. The actual response triggered depends on the wiring and the higher-level system control.

Antifreeze monitors for ventilation systems and heating coils

In ventilation and air conditioning systems, a freeze protection thermostat protects heat exchangers and heating coils that are particularly susceptible to freezing. For air-side monitoring, the temperature sensor is positioned so that critically low temperatures can be detected across the relevant range. The specific position and routing depend on the system, the airflow, and the manufacturer’s specifications.

To ensure reliable protection, the sensors, installation, and system controls must work together seamlessly. The freeze protection monitor detects and signals the risk of freezing. Measures such as opening valves, operating pumps, shutting off fans, or closing outdoor air dampers are implemented by the respective control system and must be planned on a project-by-project basis.

Select appropriate version

Self-actuated temperature monitor
Suitable version: THERMASREG® FST or FST-K without the "HR" suffix
Suitable for: applications where the device is to switch back automatically after the danger of frost has passed
Features: mechanical temperature monitoring, switching contact, capillary tube or duct version depending on the model

Compare self-actuating frost protection thermostats
Temperature limiter with manual reset
Suitable version: THERMASREG® models with the "HR" suffix
Suitable for: protective functions where deliberate inspection and manual resetting are intended after activation
Features: mechanical locking after activation, release by manual resetting

Compare frost protection thermostats with manual reset
Electronic 2-stage antifreeze thermostat
Suitable version: THERMASREG® FS20-UW, depending on the required variant
Suitable for: control concepts with additional analog signals or display
Features: depending on the version, 0–10 V inputs and outputs, switching contact and display

Compare electronic frost protection thermostats

What to look for when choosing

Monitoring task: Clarify whether the temperature is to be monitored on the air or water side. Not every version is approved for every medium.
Reset function: Decide between automatic reset and mechanical interlocking with manual reset.
Sensor design: Choose between a capillary tube sensor and a compact duct version depending on the system design.
Capillary tube length: The length must suit the area to be monitored and the intended routing. Depending on the model, 0.6 m, 1.8 m, 3 m, 6 m or 12 m are available in the range.
Output signal: Check whether a switching contact is sufficient or whether 0–10 V signals are required for the control concept.
Display: For electronic versions, a display is available depending on the model.
Environmental conditions: Check the protection rating, permitted medium, temperature range and installation requirements on the specific product page.

Selecting the Right Capillary Tube and Sensor

In the case of an antifreeze thermostat with a capillary tube, the length of the capillary tube determines which area of the heat exchanger or heating coil can be monitored. The capillary tube is routed through the relevant monitoring area in accordance with the technical design. Sharp bends, damage, and improper mounting can impair functionality and must be avoided.

When selecting a capillary tube, it is not just the maximum possible length that matters. The capillary tube must be compatible with the coil surface area, the installation path, and the specified sensor response length. The product line offers mechanical models in various lengths as well as compact duct freeze protection thermostats. Always follow the instructions for the selected model when installing, mounting, and commissioning the device.

Select a freeze protection thermostat that is compatible with the system

Whether it’s a compact duct sensor, a mechanical frost protection monitor with a capillary tube, a temperature limiter with manual reset, or an electronic solution: Choose the model based on the specific protection requirement and the existing system control. In the product grid, you can filter the available models by probe or capillary tube length, output, and display.

Compare Antifreeze Thermostats

Frequently Asked Questions About Frost Protection Thermostats and Frost Protection Monitors

Is a freeze protection monitor the same thing as a freeze protection thermostat?

In ventilation and air conditioning technology, these terms are often used to refer to the same class of equipment. “Frost protection thermostat” describes a device that operates based on temperature, while “frost protection monitor” emphasizes its monitoring function. The key factors in selecting a device are its design, sensor, reset mechanism, output, and intended application.

How does a freeze protection thermostat work?

An anti-freeze thermostat measures the temperature via a sensor. If the temperature falls below the set threshold, a switch contact or an output signal changes, depending on the model. The connected system controller processes this signal and executes the programmed protective action. This action is not determined solely by the thermostat.

Where is a freeze protection switch installed in a ventilation system?

The sensor is installed on the heat exchanger or heating coil that is at risk of freezing, in accordance with the intended monitoring method. For capillary tube versions, it is important to ensure proper distribution across the relevant area. The exact position, mounting, and wiring must be carried out in accordance with the system design and the installation instructions for the selected model.

When is a manual reset advisable?

A manual reset is useful if the system is not to be automatically reactivated after a frost protection trip. A temperature limiter with a manual reset remains locked after a trip until the cause has been investigated and the device has been manually reset. Whether this is necessary is determined by the system’s safety and control design.

We also manufacture individually

Do you have special requirements? As a manufacturer with our own production facilities in Germany, we are also able to produce products outside of the standard range at any time.

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