When planning a bathroom electrical system—especially for underfloor heating and lighting—many homeowners wonder: "Can the thermostat or the dimmer be installed inside the bathroom?"
The short answer is: Yes, but only if it meets the required safety standards and is placed in the right zone.
Understanding Bathroom Zones (BS 7671 Standard)
In the UK, bathrooms are divided into four electrical safety zones according to the IET Wiring Regulations (BS 7671). These zones define how close an electrical device can be to water and what IP (Ingress Protection) rating is required.
Zone 0
The inside of the bath or shower tray—essentially the area that can be filled with water.
Requirement: Minimum IPX7 (protection against immersion).
Voltage: Only 12V SELV (Safety Extra-Low Voltage) systems allowed.
Typical devices: Submersible LED lights.
(*The first digit after IP represents the dust protection level, and the second digit represents the water protection level. The larger the number, the higher the protection level. For example, IP47 means a dust protection level of 4 and a water protection level of 7. This article only discusses the water protection level, and the dust protection levels in the IP ratings mentioned are all replaced with X.)
Zone 1
The area above the bath or shower, up to 2.25 metres from the floor.
Requirement: Minimum IPX4 (protection against splashing water).
Typical devices: Extractor fans, waterproof light fittings.
Thermostat or dimmer: Not recommended unless IPX4-rated and certified for wet zones.
Zone 2
The area 0.6 metres beyond Zone 1 (around the bath or shower).
Requirement: Minimum IPX4.
Typical devices: Shaver sockets, IP-rated lights.
Thermostat or dimmer: Possible only if the unit is IPX4 or higher.
Zone 3/Outside Zone
Anything beyond 0.6 metres from Zone 2—essentially the dry area of the bathroom.
Requirement: IP20 or higher.
Thermostat or dimmer: Yes, this is the recommended installation zone for standard thermostats and dimmer switches.
(*This schematic diagram has been prepared in accordance with the IET Wiring Regulations (BS 7671). In case of any inconsistency or changes to the standard, the actual IET Wiring Regulations (BS 7671) shall prevail.)
Other solutions for heating
Most thermostats—including those from Repenic, Hive, and Nest—are rated IP20–IP30, which means they're not waterproof.
Installing them near water can:
Violate electrical safety regulations.
Cause moisture damage or malfunction.
Invalidate the product warranty.
Instead, the thermostat is usually mounted just outside the bathroom door, connected to:
An in-floor temperature sensor (for underfloor heating), or
A remote air sensor placed in the bathroom.
This allows precise temperature control without exposing the device to humidity.
For water underfloor heating or electric underfloor heating systems, you can use our Wi-Fi room thermostat (click here to check), which features one additional temperature sensor interface compared to other thermostats on the market. You can connect an external air sensor to this interface and install the air sensor inside the bathroom, enabling precise control of the bathroom temperature while completely avoiding potential electrical hazards.
Connect the air temperature probe to the thermostat as shown in the diagram and place it in the junction box inside the bathroom, then cover the junction box with a panel that has ventilation holes (ensuring air can flow in).
The thermostat is shipped with one 3-metre long temperature probe, which can be used as an underfloor heating sensor or an external air sensor. If you need to connect two temperature probes simultaneously, please purchase an additional one separately. The compatible temperature probe specifications for this thermostat are:
3m, NTC, R25=10KΩ±1%@25℃ B25/50=3950K±1%
3m, NTC, R25=12KΩ±2%@25℃ B25/85=3740K±2%
3m, NTC, R25=15KΩ±2%@25℃ B25/85=3740K±2%
3m, NTC, R25=22KΩ±2%@25℃ B25/85=3740K±2%
3m, NTC, R25=33KΩ±2%@25℃ B25/85=4090K±1.5%
3m, NTC, R25=47KΩ±2%@25℃ B25/85=4090K±1.5%
3m, NTC, R25=6.8KΩ±1%@25℃ B25/50=3950K±1%
3m, NTC, R25=68KΩ±2%@25℃ B25/85=4190K±1.5%
3m, NTC, R25=100KΩ±2%@25℃ B25/85=4190K±1.5%
If you do not know what heating system you are using, you can click here to refer to our other article.