Thermostat inside the bathroom, NOT outside!


When installing electric underfloor heating, for example, in a bathroom, it is also necessary to install a thermostat that will control the operation of the entire system. The question immediately arises, where to place such a device? It seems natural to install the controller in the bathroom itself. However, there is often a temptation to place it outside – for example, because of the conditions in the room. Where is the best place to put the thermostat and why? Below you will find the answer to this question.

Where to install the controller is a common dilemma for many people installing underfloor heating. Unfortunately, it leads to inexperienced installers making a serious mistake. Why?

The thermostat, according to current regulations, should always be located in the room that is controlled by it. Moreover, this has a serious technical justification, making it imperative that this rule be observed.

Electric underfloor heating with the help of heating mats or fixed heating cables must always be controlled by a thermostat with a floor temperature sensor.

Based on temperature readings, this device regulates the operation of the heating. As many as two sensors are used for this purpose: the floor sensor and the air sensor. Both of them are crucial for determining the correct operation of floor heating.


  1. All fixed-power heating mats and heating cables, according to the regulations, must be controlled by a thermostat that regulates the temperature using an external floor temperature sensor.
  2. Thermostats operating in room temperature sensing mode, must have a floor temperature limit with an additional floor sensor.
  3. The controllers must comply with the so-called Eco Design Directive, which all nVent RAYCHEM brand thermostats have, for example. It is best to use full kits available from their range (heating mats with WiFi thermostat) to ensure that all components are fully compatible with each other.

Air temperature sensor

Activation and deactivation of heating cables is usually based on air temperature. The user programs the preferred heat level for specific time intervals. When the temperature falls below the settings, the underfloor heating is activated. On the other hand, when the desired level is reached – the power is disconnected.

The air temperature sensor is located in the thermostat housing. What does this mean? That by placing the controller in another room behind a wall, it will rely on readings from another room.

Pay attention to where the thermostat is mounted on the wall:

  • Due to the risk of electric shock, do not install the thermostat in the bathroom in protection zones “0, I, II” (read more about this),
  • Do not install the thermostat in a place where there are large and frequent temperature fluctuations, such as:
    • Above the washing machine,
    • Around the radiator,
    • close to the fireplace,
    • In a place where the sun’s harsh rays fall,
    • In a place where there are drafts,
    • In a place covered with curtains, furniture, etc.

When installing a thermostat in a room such as a bathroom, increase its degree of protection against water. Standard thermostats have a degree of protection of IP21, you can increase it to IP44 by using a special seal that is mounted between the wall and the thermostat.

Floor temperature sensor

Properly installed, it reads the temperature of the floor in which the heating mats/cables are embedded. Thus, the thermostat prevents the temperature of the floor itself from rising too high. However, the sensor installed in the floor should be used as an additional protection for the floor and the heating system. Its measurements do not directly translate into the air temperature in the room, so it prevents the proper operation of electric heating mats.

Thanks to the temperature sensor in the floor:

  • We protect heating cables from getting too hot and thus burning out,
  • The floor will have an optimal temperature that will allow us to stand with bare feet,
  • protect heat-sensitive floors from deforming or changing color.
  • See how to properly install a temperature sensor in the floor.

Make no mistake: where to install the thermostat in the bathroom?

Thanks to the information you just obtained, you will no longer make the common mistake with the installation of a thermostat. This is important in terms of safety, as well as the proper operation of the floor heating system itself. The air temperature sensor, located in the controller, allows you to control the heating mats in such a way as to maintain the optimal temperature in the room.

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