Productoverview thermostats

Frequently Asked Questions

Here you’ll find answers to the most frequently asked questions about thermostats:

What is a flush-mount thermostat?
When should you choose a flush-mount thermostat?
In what applications are flush-mount thermostats used?

What is a surface-mount thermostat?
When should you choose a surface-mount thermostat?
In what applications are surface-mount thermostats used?

What is an electric thermostat?
What is a capillary thermostat?
What is a bimetal thermostat?

When should you choose an electric thermostat?
When is a capillary (mechanical) thermostat a better choice?

What is temperature monitoring and protection?
What is a safety temperature limiter (STL)?
Where are STLs primarily used?
Are there differences between an STL and a temperature limiter?
How do you choose the right temperature monitoring and protection?

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What is a built-in thermostat?

A built-in thermostat is a thermostat that is mounted inside or behind a housing, panel, or device and is typically not visible to the user. Built-in thermostats are often used as an integral part of an installation or device.
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You should choose a flush-mounted thermostat when:

• the thermostat is part of an OEM application
• protection against contact, dirt, or moisture is important
• the user is not allowed to adjust the temperature themselves
• a compact and neat finish is desired

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In what kinds of applications are built-in thermostats typically used?

• Typical applications include, for example:
• boilers and water heaters
• ovens and electric heaters
• industrial systems and machinery

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What is a surface-mounted thermostat

A surface-mounted thermostat is installed on the outside of a unit or wall and is clearly visible and accessible. The thermostat is housed in its own enclosure.
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When should you choose a surface-mounted thermostat?

• Surface-mounted thermostats are suitable when:
• the user needs to adjust the temperature regularly
• quick and easy installation is desired
• the application involves maintenance, retrofitting, or testing
• accessibility is more important than aesthetics

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In what applications are surface-mount thermostats used?

Surface-mount thermostats are often used in control panels, utility rooms, temporary installations, and in service and maintenance setups.
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What is an electric thermostat?

An electric (electronic) thermostat is a temperature controller that uses an electric temperature sensor and electronic circuitry. These thermostats offer more features than mechanical models, such as capillary thermostats or bimetallic models.
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What is a capillary thermostat?

A capillary thermostat is a mechanical thermostat that regulates temperature without electronics or an external power source. The temperature is measured by a sensor connected to a mechanical switch via a capillary tube. When the temperature changes, the circuit is automatically turned on or off.
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What is a bimetallic thermostat?

A bimetallic thermostat uses two metal strips attached to each other that have different coefficients of thermal expansion. When the temperature changes, the metals expand or contract at different rates, causing the bimetallic strip to bend. This bending is used to operate a switch, for example, to open or close an electrical contact.
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When should you choose an electric thermostat?

Electric thermostats can offer more advanced features, such as PID control, whereas simple flush-mounted or surface-mounted thermostats typically only switch on and off. This makes electric thermostats better suited for precise and demanding temperature control applications, such as programming schedules and setpoints.
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What is temperature monitoring and protection?

Temperature monitoring and protection focuses not on control, but on safety. The goal is to prevent dangerous overheating by permanently shutting down a system when a limit value is exceeded. The following components, among others, are used for this purpose:

• safety temperature limiters (STL)
• temperature limiters

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What is a safety temperature limiter (STL)?

A safety temperature limiter (STL) is a device that automatically and safely shuts down a system as soon as a preset temperature limit is exceeded. The STL operates independently of the normal temperature control system.

Features:

• permanent shutdown (manual reset or replacement required)
• increases system and process safety
• helps ensure compliance with laws and regulations

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Where are STBs primarily used?

Safety temperature limiters are primarily used in thermal oil systems, boilers, and hot water heaters, as well as in furnaces and industrial heating processes.
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Are there differences between an STB and a temperature limiter?

STB's are designed for applications with high safety requirements and have a redundant internal structure, i.e.:

• two independent measurement and processing channels
• each channel monitors the limit value separately
• relays connected in series
• an additional diagnostic channel checks plausibility

Even in the event of an internal fault, the system remains safely shut down. Mandatory for high-risk applications.

A temperature limiter has:

• no redundant design
• consists of a single measurement and switching channel
• is used for lower safety requirements. Suitable for simple protection, but not for critical processes.

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How do you choose the right safety temperature limiter?

Temperature range:

• The cut-off point is above the operating temperature
• but below the maximum allowable temperature
• for small margins → electronic STL required
• Mechanical STBs typically up to ±600°C

Response speed during rapid temperature rises:

• Use sensors with low thermal mass
• Avoid thermowells if possible
• Place the sensor as close as possible to the heat source

Switching capacity

• the STB usually switches a contactor
• In small installations, power can be switched directly
• maximum current values must not be exceeded

Internal fuse (electronic STB)

• Protects against overcurrent
• Prevents permanently closed contacts
• Replacement is necessary after tripping

Standards and certifications

Depending on application:

• DIN EN 14597 (Europe)
• ATEX (explosive atmospheres)
• UL / CSA (U.S. and Canada)

Summary

• Flush and surface mounting determine accessibility and installation
• Electrical thermostats offer accuracy and flexibility
• Temperature monitoring and protection are essential for safety
• The right choice prevents damage and complies with standards

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