A temperature controller is an electronic device that measures the temperature of a space or medium and automatically operates a heating or cooling system to hold it at a set value. In buildings, the most familiar form is the room thermostat, though the category extends to programmable controllers, zone controllers, and industrial process controllers.
Creating a comfortable, productive environment in living and working spaces has become increasingly important, and maintaining the right temperature is central to it. A temperature controller provides a practical way to hold a room at a consistent temperature while optimising energy consumption, and it is used across homes, offices, hotels, and commercial premises.
Electronic Control and Mechanical Control Are Different Things
Before going further, it is worth resolving a confusion that catches out many buyers, because two quite different families of product are described using overlapping language.
A temperature controller is an electronic device. It contains a sensor, a decision-making circuit, and an output that switches something on or off. It needs a power supply, and it can be programmed, adjusted remotely, and integrated into a wider control system.
A temperature control valve is a mechanical device. It contains a wax thermostatic element that expands and contracts with temperature, physically moving the valve without any electricity, sensor circuit, or controller. It cannot be programmed or monitored, and it cannot be switched off.
| Aspect | Temperature controller | Temperature control valve |
|---|---|---|
| Type | Electronic | Mechanical, self-acting |
| Power required | Yes | No |
| Set point | Adjustable, often programmable | Fixed or manually preset |
| What it senses | Room air, or floor via probe | The water passing through it |
| Remote monitoring | Possible | No |
| Behaviour on power loss | Stops controlling | Continues working |
| Typical role | Deciding when heat is needed | Limiting temperature at source |
These are complements rather than alternatives, and most well-designed systems contain both. The controller decides when a room needs heat; the valve limits what temperature reaches it. Our guide to temperature control valves covers the mechanical side in detail.
Main Features of a Temperature Controller
Features vary considerably between models, and understanding what each does makes the specification decision clearer.
Temperature setting
Users set the desired temperature and the device holds the room close to that value. How closely it holds is expressed as control accuracy, and quality units achieve ±1°C.
Sensors
Controllers measure temperature using sensors such as NTC thermistors, providing real-time data to the control circuit.
Two sensor arrangements are common and the distinction matters in underfloor heating. An internal sensor in the controller body measures room air temperature. An external floor probe measures the floor itself. Better controllers support both simultaneously, which allows the unit to control room air temperature while independently capping floor surface temperature. That second function protects temperature-sensitive floor coverings such as engineered wood from cupping or gapping.
Thermostat function
Many temperature controllers act as thermostats, automatically operating the heating or cooling system to reach and maintain the set temperature.
User interface
Interfaces range from rotary knobs to button panels with LCD displays. The choice is not merely cosmetic. A rotary knob is more intuitive for users unfamiliar with digital menus and works better with wet hands, which matters in a bathroom. A button panel with a display offers more configuration options and suits users comfortable with digital interfaces.
Programmed settings
More advanced controllers allow different temperature settings for different times of day or days of the week, which matches heating to occupancy rather than running it continuously.
How well this works depends on the system it controls. A fast-responding radiator system suits deep setbacks, since it recovers quickly. A high thermal mass underfloor system performs better with steady operation and modest setbacks, because it takes hours to respond and continues releasing heat after the system stops.
Compatibility
Controllers can be compatible with various HVAC systems including underfloor heating, central heating and cooling, and split or mini-split ductless systems.
Two compatibility details determine whether a controller will actually work in your system. The operating voltage must match your wiring, typically 230VAC in European residential systems or 24V where a central controller is used. And the output capacity must be sufficient for what it drives, whether that is a single thermal actuator, several actuators, or a direct electric heating load.
Remote control and smart home integration
Some modern controllers offer remote adjustment through an app, and some integrate with smart home ecosystems for voice control and centralised monitoring.
The Control Chain: How Temperature Control Actually Works
This is where a single controller becomes a system, and understanding the chain explains why specifying the controller alone is not enough.
In a hydronic heating installation, temperature control happens through a sequence of components, each with a distinct role:
1. The room thermostat measures the temperature in its zone and decides whether heat is required. It does not move any water itself; it produces a demand signal.
2. The base station receives demand signals from every thermostat in the building and coordinates the response. It powers the correct actuators, and importantly it can also signal the heat source to start, so the boiler or heat pump runs only when a zone genuinely calls for heat rather than cycling regardless.
3. The thermal actuator sits on the manifold branch valve for that zone. When energised, a PTC element warms a wax capsule which expands and drives a piston, opening the valve so warm water flows into that circuit.
4. The manifold distributes flow between the individual floor loops, with each branch controlled independently.
5. The mixing valve sits upstream of all this, mechanically limiting the water temperature entering the floor regardless of what the electronic controls are doing.
Why the chain matters when specifying. A thermostat is only as useful as what it can drive. If its output cannot power the number of actuators on your manifold, the zone will not open. If its voltage does not match the wiring centre, it will not integrate at all. And a system with excellent thermostats but no coordination between them will run the heat source whenever any single zone calls, which wastes energy. Specify the chain together rather than the controller alone.
Legom manufactures every element of this chain at the same facility, covering room thermostats, base stations, thermal actuators, and manifolds, which means compatibility is designed in rather than assumed.
Types of Temperature Controller
Non-programmable thermostats hold a single set temperature until changed manually. Simple, inexpensive, and adequate where occupancy is consistent.
Programmable thermostats allow scheduling across the day and week, matching heating to when the space is actually used. This is where meaningful energy savings sit in a building with predictable occupancy patterns.
Smart and connected thermostats add app control, remote monitoring, and integration with home automation platforms. Their value is greatest where occupancy is unpredictable, since the schedule can be changed from anywhere.
Zone controllers and base stations coordinate multiple thermostats across a building, which is what turns individual room control into a functioning multi-zone system.
Industrial process controllers, including PID controllers, hold a process temperature to tight tolerance in manufacturing applications. These are a different product category from building controls, though the underlying principle is the same.
Benefits of a Temperature Controller
Energy efficiency
A controller ensures the heating or cooling system operates only when needed rather than running continuously. That regulation reduces energy waste, lowers utility costs, and reduces environmental impact.
Zone control extends this considerably. Where a single thermostat heats the whole building to one temperature, zone control lets bedrooms run cooler than living areas and unused rooms go unheated entirely. In a multi-room property, this is where much of the available saving actually sits.
Consistent comfort
Users set the desired temperature and the controller maintains it, absorbing the fluctuations that would otherwise be felt as the space warming and cooling through the day.
Automation
Scheduling reduces the need for manual adjustment, and remote-capable controllers allow monitoring and adjustment from off site. For a household with irregular hours, this converts a system that must be remembered into one that simply works.
Protection of the building fabric
Worth noting because it is often overlooked. Where a floor probe is used, the controller caps floor surface temperature, protecting timber and engineered wood coverings from heat damage. And a controller with a low-temperature limit can hold a minimum temperature in an unoccupied property, preventing pipes freezing without heating the building fully.
One clarification worth making. A temperature controller regulates temperature, not humidity or air quality. Controlling humidity requires a humidistat and a humidifier or dehumidifier, and introducing fresh air requires a ventilation system. These are frequently discussed together because all three affect comfort, but they are separate devices with separate controls, and specifying a thermostat will not address a humidity or ventilation problem.
How to Choose a Temperature Controller
Five questions settle most specifications.
1. What system does it control?
Hydronic underfloor heating, radiators, electric heating, or a reversible heating and cooling system each impose different requirements. Underfloor heating benefits from floor probe capability; a reversible system needs heating and cooling modes; electric heating requires a controller with sufficient switching capacity for the load.
2. What does it need to drive, and at what voltage?
Confirm both the operating voltage and the output capacity. A thermostat driving five actuators on a large open-plan zone needs greater capacity than one driving a single actuator. A controller switching an electric heating circuit directly needs a load rating appropriate to that circuit.
3. Does the system need automatic heating and cooling changeover?
Where a central signal switches the whole system seasonally, as in reversible heat pump installations, the thermostat needs a changeover terminal. Not all models have one, and this cannot be added later.
4. Who will use it?
A rotary knob suits users unfamiliar with digital menus and wet-hand environments. A button panel with a display suits those comfortable with configuration. Child lock matters in hospitality, care settings, and family homes where temperature limits need enforcing.
5. Is scheduling required?
Programmable control delivers savings where occupancy follows a pattern. Where the building is occupied continuously, the benefit is smaller and a simpler unit may suffice.
The Legom Room Thermostat Range
Legom manufactures four room thermostat models for water-based underfloor heating, electric heating, and radiant cooling systems, all CE and RoHS certified, compatible with NTC sensors and Legom thermal actuators, and available for OEM and ODM customization.
| Feature | Apus RT-A1 | FC FC1D | Volcano RB-2305HT | RT-X1 Ascent |
|---|---|---|---|---|
| Interface | Rotary knob | Button panel | Circular display | Button and LCD |
| Voltage | 230VAC | 100–240VAC | 100–240VAC | 230VAC |
| Heating and cooling | Yes | Yes | Yes | Heating only |
| 7-day programmable | No | No | No | Yes, 6 periods |
| Auto CO changeover | No | Yes | No | No |
| Max actuators | 5 | Standard | Standard | 16A direct load |
| Electric heating | No | No | No | Yes, 3680W |
| Dual sensor mode | Standard | Internal and external | Both simultaneously | Both with floor limit |
| Child lock | No | Yes | No | Yes |
| Accuracy | Standard | Standard | ±1°C | ±1°C |
| Colours | White, black | White, black | White, black, grey | White |
| Base station compatible | Yes | Yes | Yes | Standalone |
Matching a model to the application
The Apus RT-A1 is the choice where a tactile rotary interface suits the user, and it carries the highest actuator capacity at five simultaneously, which suits large or open-plan zones served by several manifold loops.
The FC FC1D is the only model with an automatic changeover terminal, which makes it the specified choice for reversible heat pump installations with seasonal switching. Its child lock and wide 100 to 240VAC range also suit hospitality and multi-market supply.
The Volcano RB-2305HT offers ±1°C accuracy, three colour options, and dual sensor operation running both sensors simultaneously, which allows room air control with independent floor temperature capping.
The RT-X1 Ascent is the only programmable model, combining a seven-day schedule with six periods per day and a 16A switching capacity that drives both hydronic and electric heating up to 3680W. It has the most extensive parameter set in the range at ten configurable items.
“The mistake I see most often in specification is treating the thermostat as a standalone purchase. Someone chooses a good controller, fits it, and then finds it will not drive the actuators on their manifold, or the voltage does not match the wiring centre, or there is no changeover terminal and the system needs seasonal switching. None of those are faults in the thermostat. They are consequences of specifying one link in a chain without checking the rest of it. The questions worth asking before you order are what voltage, how many actuators, and does the system switch between heating and cooling. Three questions, and they settle almost every case.”
— Maggie Shen, Director of Legom
Choosing the Right Controller for Your Space
Temperature controllers have changed how climate control is managed in buildings. By providing precise regulation, they increase comfort, improve energy efficiency, and support healthier living and working environments.
When choosing one, consider the specific needs of the room, the type of HVAC system it will control, and the features that suit how the space is actually used. The options available, from simple thermostats through programmable and smart controllers, cover a wide range of requirements, and the right choice is the one matched to the system rather than the one with the longest feature list.
Legom supplies room thermostats and the complete control chain to partners in more than 90 countries, produced at our facility in Jiaxing, Zhejiang Province. OEM and ODM services cover firmware parameter defaults, housing colour, display language, button layout, and packaging for private-label supply. Contact the technical team to discuss specification.
Frequently Asked Questions
What is a temperature controller?
An electronic device that measures the temperature of a space or medium and automatically operates a heating or cooling system to hold it at a set value. In buildings the most familiar form is the room thermostat, though the category also covers programmable controllers, zone controllers and base stations, and industrial process controllers. All work on the same principle: sense the current temperature, compare it against a target, and switch the heat source or a zone valve accordingly.
What is the difference between a temperature controller and a temperature control valve?
A temperature controller is electronic. It has a sensor, a control circuit, and an output, requires power, and can be programmed and monitored remotely. A temperature control valve is mechanical, using a wax thermostatic element that expands with temperature to move the valve without any electricity. The controller decides when a room needs heat; the valve limits what temperature reaches it. They are complements rather than alternatives, and most well-designed hydronic systems contain both.
Does a temperature controller control humidity?
No. A temperature controller regulates temperature only. Controlling humidity requires a humidistat together with a humidifier or dehumidifier, and introducing fresh air requires a ventilation system. These are often discussed together because all three affect comfort, but they are separate devices with separate controls. Specifying a thermostat will not address a humidity or ventilation problem, and it is worth being clear about this before purchase.
What is a floor sensor and do I need one?
A floor sensor is an external probe that measures the floor temperature directly rather than the room air. In underfloor heating it serves two purposes: it allows the controller to cap floor surface temperature, protecting temperature-sensitive coverings such as engineered wood from cupping or gapping, and it gives more accurate control of the floor itself. Better controllers run both an internal air sensor and an external floor probe simultaneously, controlling room temperature while independently limiting the floor.
How many actuators can one thermostat drive?
It depends on the model’s output capacity, and this is a specification worth confirming before ordering. A standard thermostat typically drives one actuator, which suits a single-loop zone. Larger or open-plan spaces served by several manifold loops need a thermostat with higher capacity, such as the Legom Apus RT-A1 which drives up to five simultaneously. Exceeding the rated capacity means the actuators will not open reliably, and the symptom appears as a zone that never reaches temperature.
What is automatic changeover and do I need it?
Automatic changeover allows a thermostat to switch between heating and cooling mode on receiving a signal, typically at 230V, rather than requiring manual selection. It matters in reversible systems such as heat pump installations where the whole building switches seasonally. Only some models have a changeover terminal, and it cannot be added afterwards, so if your system needs it the requirement must be identified at specification stage. The Legom FC FC1D is the model in the range with this capability.
Is a programmable thermostat worth it?
It depends on occupancy and on the system. Where the building is empty for predictable periods, scheduling delivers real savings by avoiding heating an empty space. Where it is occupied continuously, the benefit is smaller. The system type matters too: a fast-responding radiator circuit suits deep setbacks since it recovers quickly, while a high thermal mass underfloor system performs better with steady operation and modest setbacks, because it takes hours to respond and continues releasing heat after the system stops.
Can one thermostat control the whole house?
It can, but it means every room follows whatever that one room needs. The room with the thermostat reaches temperature and the system stops, regardless of whether other rooms are warm or cold. Zone control with a thermostat per area and a base station coordinating them lets bedrooms run cooler than living areas and unused rooms go unheated entirely. In a multi-room property, that is where a substantial share of the available energy saving actually sits.
What voltage do I need?
Match it to your wiring centre or controller output. Most European residential systems use 230VAC thermostats wired directly. Systems using a central heating controller or smart home platform often operate at 24V. Some models such as the Legom FC FC1D and Volcano RB-2305HT accept a wide 100 to 240VAC range, which simplifies supply into markets with differing mains voltages. Confirm the output voltage specification of your controller before ordering rather than assuming.
Reviewed by Maggie Shen, Director at Legom, on August 15, 2026. This guide to temperature controllers was reviewed for technical accuracy, including the distinction between electronic and mechanical temperature control and the scope of what a thermostat does and does not regulate.