How to choose a thermostat for underfloor heating: what to pay attention to

We are still preparing products.

But you can look at other categories.

How to choose a thermostat for floor heating: what to pay attention to

Floor heating is today one of the most comfortable heating systems you can have in a house or apartment. Heat spreads evenly from the floor upwards, the temperature of the head and feet is balanced, and there are no hot radiators that children could bump into. But when it comes to "floor heating," most people think only about the distribution system or the electric heating cable. The thermostat is often forgotten – and yet it is precisely the thermostat that determines whether the entire system works efficiently, economically, and safely, or whether the floor overheats the surface, damages the wooden flooring, and unnecessarily inflates the electricity bill.

In this article, we will comprehensively go through the entire selection process – from understanding the basic principles, through technical parameters that must match the specific installation, to practical tips from projects I have seen on site. Whether you are solving an electric floor in the bathroom, a water system with a manifold, or a renovation of an apartment with wooden flooring – after reading this text, you will know exactly what to look for.

Why choosing a thermostat for floor heating is different from radiator heating

A thermostat for a radiator or boiler primarily works with the air temperature in the room. It measures the surrounding air, compares it to the set value, and turns the heat source on or off. In the case of floor heating, the situation is more complex for several reasons:

Thermal inertia of the floor. A stone or concrete floor with a mat in anhydrite reacts to a change in setting for several tens of minutes to an hour. The thermostat must be able to work with this.
Protection of the floor covering. Wooden floors, laminate, and cork coverings must have a limit on the maximum surface temperature (typically 27 °C in living areas, 33 °C in edge zones). A standard room thermostat cannot monitor this – you need a floor sensor and a thermostat that can evaluate it.
Switching capacity. Electric floor heating can have a power of 150–250 W/m², which in a standard bathroom of 5 m² is 750–1,250 W. In a living room of 25 m², it can be 3,750 W and more. The thermostat must have contacts that can handle this load without overheating.
Type of load. Heating mats and cables are purely resistive load (cos φ = 1), which is more favorable for switching contacts than motor load, but high current requires a properly dimensioned thermostat.

These topics are discussed in more detail in other articles in the Knowledge Center – specifically Switching capacity of a thermostat for floor heating: how to determine it correctly and Floor thermostat with floor sensor vs. air sensor: the difference and when to use which. Here, we will address them in the context of overall selection.

Types of thermostats for floor heating – overview and differences

There are essentially four basic categories of thermostats on the market, which differ in functions, price, and suitability for different applications.

1. Simple analog thermostats

Traditional bimetallic or capillary thermostats are becoming less common today. Their accuracy is low (hysteresis ±1.5–3 °C), they do not allow programming, and they do not have an LCD display. For floor heating, I recommend them today only for low-demand applications in cottages or workshops, where the main goal is to prevent freezing. I would not use them in a household today.

2. Electronic thermostats without programming

This is today the basic standard for most apartment installations. It measures temperature with digital sensors (NTC 10 kΩ or 12 kΩ, depending on the manufacturer), displays the actual temperature on an LCD or LED display, and switches the contact with an accuracy of ±0.5 °C. The advantage is simple operation – you set one value, and the thermostat works. The disadvantage is precisely that it cannot adapt the temperature to the daily schedule.

A typical example of this segment is SALUS RT10-230V – a compact electronic thermostat that can handle a load of up to 16 A (3,680 W), has an input for a floor sensor NTC 10 kΩ, and can work in three modes: air only, floor only, or air with floor temperature limitation. For a bathroom or a children's room without the need for programming, this is a solid choice at a reasonable price.

3. Programmable thermostats

They allow you to set different temperature values for individual time blocks – before waking up in the morning, during the day, in the evening, at night, on weekends. A good 7-day program can save 15–25 % energy compared to thermostats running at a constant temperature, without any comfort compromise. The advantage is also that you don't have to worry about manually lowering the temperature when you leave the house – the program does it automatically.

Examples in this segment are thermostats SALUS ERT20 - 230V and SALUS ERT50 - 230V. Both have weekly programming, an input for a floor sensor NTC 10 kΩ, and a switching capacity of 16 A. ERT50 offers a larger and more readable display and more programming blocks per day compared to ERT20. For a living room or bedroom, where the daily rhythm repeats regularly, a programmable thermostat is always worth it – the additional investment compared to the basic model pays off within one heating season.

4. Smart thermostats (Wi-Fi, ZigBee, Z-Wave)

Thermostats controllable via a mobile app, voice assistants, or integrable into home automation. They allow you to change the temperature remotely (excellent when coming home unexpectedly), display consumption history, and some have a geofencing function – they automatically know when you are approaching home. The price is higher, but for modern homes with intelligent electrical installations, it is a standard. An example is Jablotron AC-83, which, in addition to wireless communication and an intuitive display, stands out for its advanced adaptive regulation, where the thermostat itself calculates when to start heating to reach the set temperature exactly at the desired time.

Key technical parameters – what you need to know before purchasing

Switching power and maximum current

This is the most important thing. A thermostat that does not have a sufficiently powerful contact for your installation will overheat the contacts, shorten its lifespan, and in the worst case cause a fire. The switching current of the thermostat must be higher than the actual current draw of your heating system, ideally with at least a 20% reserve.

Practical example: A bathroom of 6 m², with a heating mat with a specific power of 150 W/m². Installed power = 6 × 150 = 900 W. Current = 900 / 230 = 3.9 A. A thermostat with a 10 A contact is sufficient in this case. However, if you are dealing with a living room of 20 m² with a power of 150 W/m², you have 3,000 W and a current of 13 A – here you need a thermostat with a contact of at least 16 A, or use a relay and use the thermostat only as a control signal. This topic is discussed in more detail in the article Switching power of a thermostat for underfloor heating: how to determine it correctly.

Type of sensor – air vs. floor

There are three scenarios for temperature control for underfloor heating:

Air sensor (built into the thermostat): The thermostat measures the air temperature in the room and maintains it at the set value. The floor can heat up more than is appropriate for the covering. Suitable for tiles and concrete, where there is no risk of damaging the covering.
Floor sensor (external NTC sensor): The thermostat measures the temperature directly in the floor and maintains it at the set value, regardless of the air temperature. Advantageous for protecting coverings and in rooms where the air temperature is not stable (hall, entrance, greenhouse).
Combined mode (air + floor sensor): The thermostat regulates according to the air temperature, but also monitors the floor temperature and turns off the heating if it would exceed the set limit – regardless of the air temperature. This is the ideal mode for wooden floors, laminate and cork. Very important: in this mode, you must correctly set both limits – the target air temperature and the maximum floor temperature.

More on this topic can be found in the article Thermostat with floor sensor vs. air sensor: difference and when to use which.

NTC sensor resistance – you must ask before purchasing

External floor sensors are NTC thermistors – resistance decreases with increasing temperature. The problem is that different thermostat manufacturers use different characteristics: the most common are NTC 10 kΩ (at 25 °C), but 12 kΩ or 15 kΩ also occur. If you have inherited an old installation with a built-in sensor, or you are buying a sensor from another manufacturer, check compatibility. An incorrect NTC resistance will cause the thermostat to measure inaccurately – for example, it will display 28 °C when the actual floor temperature is 24 °C. Most thermostats from SALUS and Jablotron available at atria.sk use NTC 10 kΩ, which is currently the most common standard.

Control hysteresis

Hysteresis indicates how many degrees the temperature must drop below the set point for the thermostat to turn on again. For example, with a hysteresis of 0.5 °C and a set temperature of 22 °C, the thermostat will turn on at 21.5 °C and turn off at 22 °C. Low hysteresis = more precise control = more comfortable heat, but also more switching cycles. For underfloor heating with its thermal inertia, an optimal hysteresis is 0.5–1 °C. Cheap thermostats with a hysteresis of 2–3 °C will cause more noticeable heat pulsing.

IP protection and environmental resistance

For bathrooms and areas with increased humidity, at least IP21 protection (protection against dripping water) is necessary. In the wet part of the bathroom (within 0.6 m from the sink or above the bath), the requirements are even stricter – IP44. Most standard thermostats are intended for dry areas (IP20), so install models with specified IP protection in the bathroom or place the thermostat outside the wet zone (in the hallway, at the entrance to the bathroom).

Floor covering and maximum temperature – what should not be underestimated

This is an area where the most mistakes are made – even by experienced installers. Each floor covering has a maximum allowable surface temperature specified by the manufacturer in the technical documentation. Exceeding this temperature leads to deformation, cracking of joints, peeling of varnish, and voids the warranty on the floor covering.

Ceramic tiles: practically no limitation (up to 40 °C and more), regulation according to comfort
Stone floor (marble, granite): no temperature limitation, sensitivity to rapid temperature changes
Concrete screed without covering: no limitation
Floating laminate on floor heating: max. 27–29 °C surface temperature (depends on manufacturer and certification)
Massive wooden floor: max. 27 °C surface temperature, humidity control is also important
Cork: max. 27 °C, some manufacturers specify 26 °C
Vinyl, PVC, LVP: 28–30 °C, always check the manufacturer’s certificate for the covering

From practice: I have experienced a renovation where the customer had newly laid floating laminate and an old analog thermostat without a floor sensor. The thermostat controlled heating based on air temperature – and since it was cold, it heated continuously. The floor heated up to 34 °C, the planks started to warp and the joints cracked. Damage of several hundred euros, plus reinstallation. A thermostat with a floor sensor and a set limit of 27 °C would have eliminated the whole problem.

Therefore, for wooden and laminate floors, always choose a thermostat that has an input for a floor sensor and the ability to set the maximum floor temperature – either in a combined mode or in a pure floor heating mode with a set limit.

Thermostat selection according to heating system type

Electric floor heating (heating mat or cable)

Electric floor heating is controlled exclusively by a thermostat – the heating element is directly connected to the thermostat’s output contact. Here it applies that the thermostat’s power must match the full power of the mat or cable. Most electric floor heating systems operate on 230 V, less frequently three-phase (400 V) for larger areas.

For a bathroom (typically up to 800 W), a thermostat with a 10 A contact is sufficient. For larger areas (living room, hall) of 2,000 W or more, I recommend a 16 A thermostat, or a solution with a relay – the thermostat switches the relay coil (low current, a few hundred mA), and the relay then switches the power circuit. This is especially important for three-phase systems, where standard apartment thermostats are not sufficient.

For a simple bathroom without special programming requirements, the SALUS RT10-230V has proven to be effective – simple, reliable, with a floor sensor included. For households where you want energy savings through programming, the SALUS ERT50 - 230V with a clear display and 6 temperature blocks per day is an excellent choice.

Water-based floor heating (low-temperature system)

In this case, the thermostat does not directly control the boiler’s power, but controls an electric actuator on the manifold – when the room temperature is lower than set, the thermostat sends 230 V or 24 V voltage to the actuator, which opens the corresponding circuit and hot water starts to circulate. The boiler is controlled by its own control system or by a combined contact from the thermostats.

For water-based floor heating, it is crucial:

The thermostat must have an output compatible with the actuator (230 V or 24 V – always check the actuator voltage!)
The actuator load is small (5–8 W), but with a larger number of rooms, the total power of the actuators must be considered
For programmable systems with a return signal from the thermostats, thermostats with a relay contact or special system solutions are recommended

For water-based floor heating, the Jablotron AC-82 is suitable – a first-class thermostat with adaptive control, which is a huge advantage for a system with a large thermal inertia. The thermostat learns by itself when to start opening the valve to achieve comfort exactly at the set time.

Programming and energy savings – how it works in practice

Many customers ask whether a programmable thermostat is really worth it compared to a simple one. The answer depends on your lifestyle, but in most households, yes. Let’s look at a concrete example:

A family leaves for work at 7:30, returns home around 17:00, and goes to bed at 23:00. With a constant thermostat set to 21 °C, the heating runs even during the day when no one is at home. A programmable thermostat would set:

5:30 – 7:30: 21 °C (morning wake-up)
7:30 – 16:30: 16 °C (reduction during the day when no one is at home)
16:30 – 23:00: 21 °C (evening comfort, with preheating half an hour before arrival)
23:00 – 5:30: 18 °C (night temperature)

Lowering the temperature by 1 °C saves about 6 % of energy. A 9-hour daily setback from 21 °C to 16 °C (a difference of 5 °C) theoretically saves 30 % during that time. On an annual average, this means 15–20 % of total consumption for floor heating. For an electric underfloor heating system with a monthly consumption of 80–120 €, this can be 15–25 € per month, i.e., 150–250 € per season – returning the investment in a thermostat within a few months.

Important note: with water-based floor heating, the thermal inertia is much greater than with electric systems. A system in a thick slab requires hours to heat up and hours to cool down. Too aggressive night setbacks (a drop of more than 2–3 °C) may not be beneficial, as the energy used to reheat can outweigh the savings. For water-based floor heating, thermostats with adaptive start function (autolearning) – such as Jablotron AC-82 – are more suitable, as they learn when to start heating so that you are not in a cold room in the morning.

Installation and wiring – practical guidelines

A thermostat for floor heating is mounted in a standard electrical box (junction box) in the wall – just like a regular switch. Most models are designed for a box depth of 40–50 mm (so-called shallow or deep). The installation height is typically 1.0–1.2 m above the floor (ergonomic position for operation), but otherwise not normatively restricted (except in bathroom zones).

The floor sensor is placed in a protective tube (pipe) with a diameter of 8–10 mm, which is embedded directly in the floor and leads to the thermostat box. Correct placement of the sensor is important – it must be in the center of the heating loop, not directly on the heating cable or in the gap between cables. The depth should be such that the sensor measures the temperature of the mortar, not the surface. More on the topic can be found in the article Setting up the floor temperature sensor: correct depth and placement.

Never connect an electric underfloor heating system directly to an outlet using an extension cord. It requires a fixed connection via a terminal block or directly to the distribution board. Joints and terminal blocks must be in a box in the floor (larger volume), not in the plaster. The supply cable must match the total power – for a load up to 2 300 W, CYKY 3×1.5 mm² is sufficient, for higher power use 3×2.5 mm². A detailed step-by-step procedure can be found in the article Installation of a thermostat for underfloor heating: step-by-step guide and Wiring of a thermostat for underfloor heating: diagram and most common mistakes.

What to pay attention to when choosing a specific model – checklist

Before making a final decision, go through these points:

Power of your underfloor heating [W] → calculate the current (A = W / 230) and compare it with the maximum switching current of the thermostat. Always with a 20–25 % reserve.
Type of floor covering → wooden, laminate, cork: floor sensor and floor limit setting are mandatory. Tiling: you can control only by air.
Type of heating system → electric mat = direct switching, water heating = actuator control, check the actuator voltage (230 V or 24 V).
Need for programming → if you are at home irregularly, want night reduction or different temperatures during the day: choose a programmable model.
Smart functions → if you have a smart home or want control from a mobile device: choose a Wi-Fi model.
IP protection → bathroom = min. IP21, wet zone = IP44 or installation outside the zone.
NTC sensor resistance → check whether the new sensor matches the characteristics of the thermostat (most commonly 10 kΩ at 25 °C).
Aesthetics and size of the box → matching with existing switches (Schneider, Legrand, ABB frames...). Some thermostats offer interchangeable frames.

Most common mistakes when choosing a thermostat in practice

Over the years of practice, I have seen these recurring mistakes:

1. Too weak a thermostat for a large area. A customer buys a 10 A thermostat for a 2 200 W mat (current 9.6 A) – it works on paper, but without a reserve. Contacts overheat, lifespan decreases, and the thermostat fails after 2–3 years. Solution: for power above 1 800 W, always use a 16 A contact.

2. Forgotten protective tube for the sensor. A sensor embedded directly in the slab without a protective tube cannot be replaced without breaking the floor. Always install the sensor in a protective tube with an accessible end at the thermostat box.

3. Thermostat in an unsuitable location. A thermostat behind a curtain, in a cabinet, or where the sun shines on it – the air sensor measures the wrong temperature and heating does not work properly. The thermostat must be in a representative location in the room, away from direct sunlight, drafts, and heat sources.

4. Incorrectly set floor limit. A customer sets the floor limit to 35 °C for a laminate floor. The laminate manufacturer recommends 27 °C. Result: deformation and loss of warranty. Always read the floor covering documentation.

5. Ignoring sensor compatibility. An old thermostat had an NTC 12 kΩ, the new one has an NTC 10 kΩ. The customer uses the original embedded sensor with the new thermostat – the measurement is inaccurate by 2–3 °C, and heating does not work properly. When replacing a thermostat, always check the sensor type or replace it as well.

Comparison: SALUS vs. Jablotron – briefly on selection

In the atria.sk range, two strong brands are represented – SALUS and Jablotron. Both are reliable European products, but they have different focuses. SALUS is oriented towards cost-effective, simple and straightforward solutions – ideal for standard apartments and houses without the need for advanced automation. Jablotron is a premium line with a focus on intelligent regulation, adaptive functions, and integration into systems.

For a standard bathroom without programming: SALUS RT10-230V. For a living room with a program: SALUS ERT50 - 230V. For a smart home or water heating with adaptive start: Jablotron AC-82 or Jablotron AC-83. A detailed comparison can be found in the article Thermostat SALUS vs. Jablotron for underfloor heating: model comparison.

Common questions (FAQ)

Do I need to use a thermostat with a floor sensor for electric underfloor heating, or is an air sensor sufficient?

It depends on the floor covering. If you have tile or concrete floor, an air sensor is sufficient – you just set the desired air temperature and the thermostat works. If you have laminate, wood, cork, or vinyl, a floor sensor is a necessity – it protects the floor covering from overheating. The ideal is a combined mode: the thermostat regulates according to air, but also monitors the maximum floor temperature and turns off the heating if it is reached, regardless of the air temperature.

What power (switching current) should the thermostat have for a 5 m² bathroom with a mat of 150 W/m²?

Total power of the mat: 5 × 150 = 750 W. Current: 750 / 230 = 3.26 A. A thermostat with a 10 A contact is therefore more than sufficient. In case you later add more area, or if the mat has a higher specific power (200 W/m² = 1 000 W, current 4.35 A), 10 A is still sufficient. For larger areas (over 8–10 m²) or power over 1 800 W, always go for a 16 A thermostat.

Can I connect the thermostat for underfloor heating myself, or must an electrician do it?

According to current legislation in Slovakia, only a qualified person (electrician with appropriate qualifications) may perform fixed electrical installations (230 V), including the connection of a thermostat and heating mat. If you install it yourself and a fire or other incident occurs, the insurance company may refuse to pay. You can mount the thermostat mechanically (install it in the box), but the actual connection to the electrical network should be done by an electrician and a revision report issued.

What is adaptive regulation and when is it suitable?

Adaptive (or "autolearning") regulation means that the thermostat learns the thermal inertia of your room and heating system on its own. When you set that you want 22 °C at 7:00, the thermostat automatically determines that your system needs to start heating at 5:30 to actually reach the desired temperature by 7:00. It is particularly suitable for water-based floor heating (large thermal inertia) and for programmable thermostats in rooms with poor thermal insulation. For electric underfloor heating with low thermal mass (thin mat in a bathroom), adaptive regulation is less important.

How much does replacing a thermostat for underfloor heating cost – is it worth buying an expensive model?

The prices of thermostats in the category for underfloor heating range from about 15–25 € (simple electronic) up to 80–150 € (smart Wi-Fi model). Replacing a thermostat without the need for demolition is a quick and cheap job for an electrician (1–2 hours). A more expensive programmable model will pay for itself within one heating season if you have a regular daily routine. A smart model also brings the comfort of remote control – if it fits your lifestyle, it is a worthwhile investment. Never skimp on switching capacity – this is the only parameter where cutting costs directly endangers safety.

Can one thermostat control multiple rooms or several mats at once?

One thermostat (one sensor, one contact) can be physically located in only one room and controls heating according to the temperature there. If you want to control multiple rooms independently, each one needs its own thermostat. An exception is a situation where the heating mats in two rooms behave as one circuit and are connected in series or in parallel – but even then, the total power must be within the switching capacity of a single thermostat. For large projects (single-family house, multiple rooms), control units with multiple inputs from individual room thermostats are used – but that is a topic for system solutions beyond the scope of this article.

Conclusion: a well-chosen thermostat is an investment, not just an accessory

Underfloor heating without a properly chosen thermostat is like a car without a speedometer – it might work, but you will be blindly guessing what is happening. A thermostat is not just a switch – it is the brain of your underfloor heating system, deciding on comfort, efficiency, and the safety of the entire system.

When choosing, prioritize the type of flooring and the need for floor protection, switching capacity matching the power of the mat, sensor compatibility, and finally the type of regulation (simple, programmable, smart). Do not buy a thermostat based on price and design – buy based on parameters that match your specific installation.

If you are unsure, take a look at the entire category of thermostats for underfloor heating and compare the technical specifications of individual models. If you have any doubts,

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.