Where to put an underfloor heating thermostat

A thermostat only knows the temperature of the air or floor right next to its sensor. If that spot is warmer or colder than the rest of the room, the heating switches off too early or runs too long. With underfloor heating this matters more than with radiators, because the floor responds slowly. A bad reading can leave a room cold for hours before anyone notices.

This guide covers the best height and wall, places to avoid, open-plan rooms, bathrooms and kitchens, and where to put the floor probe. If you are still choosing the thermostat itself, see our guide to wired, wireless and smart UFH thermostats.

What height should an underfloor heating thermostat be?

Around 1.4 to 1.5m from the floor in an existing home, and no higher than 1200mm to the top of the control in a new home built to Approved Document M. The common 1.5m figure comes from the fact that cold air settles low and warm air rises, so a thermostat near the floor or the ceiling gives a false reading.

Source or situation	Recommended height
General thermostat guidance	About 1.5m from the floor
Heatmiser thermostats and Thimble Sensor	Around 1.4m from the ground
Heatmiser neoStat manuals	Eye level
New dwellings (Approved Document M)	Switches and controls between 450mm and 1200mm above finished floor

The IET explains that in new dwellings, switches and controls should sit between 450mm and 1200mm above finished floor level, with 1200mm the maximum to the top of a control. In existing homes, replacement accessories can match the height of what is already there. If the home needs to suit a wheelchair user, keep the thermostat below 1.2m whatever the age of the building.

A practical tip: line the thermostat up with the light switch by the door, as long as that wall is not draughty. It is easy to find, it looks tidy and the cable route is often already there.

Where should you not put an underfloor heating thermostat?

Do not put it anywhere it can feel heat, cold or sun that the rest of the room does not. Thermostat makers and suppliers agree on the same list:

• Near a heat source. Not above a radiator, next to a cooker, fire, TV or lamp. The thermostat warms up and switches off before the room is warm.
• In direct sun. Sun on the case can make the room look warmer than it is and switch the heating off early, even on a cold day.
• In a draught. Not beside an outside door, a window that opens or an air vent. Halls are often draughty for this reason.
• On a cold outside wall. External walls and thermal bridges are cooler than the room air and can make the heating run on.
• Behind curtains or furniture. Heatmiser asks for free airflow around the thermostat, so keep sofas, shelves and curtains clear of it.
• Plastered into the wall. A sensor buried in the wall reads the wall, not the room.

Two smaller points help accuracy. If the thermostat sits on a back box, seal or insulate the box so cold air from the cavity does not blow through it. And a flush neoStat needs a back box at least 35mm deep, so plan that before the plasterer arrives.

Does every room with underfloor heating need its own thermostat?

In most cases, yes. Part L of the Building Regulations expects each room to have its own thermostatic control when a full heating system is put into a new home, and when the heat source is replaced in an existing home. With radiators this is often met with TRVs. With underfloor heating it normally means one room thermostat per room or zone, each switching its own actuators at the manifold.

There are limited exceptions. BEAMA's Part L guidance gives the example of a single-storey open-plan home where the living area is more than 70% of the floor area. If you plan to run two rooms from one thermostat, check with your building control body that it meets the rules on your job first.

Each thermostat is wired back to a wiring centre by the manifold, which opens that room's actuators and starts the pump and heat source. Our guide to UFH zoning and wiring centres shows how it fits together.

Where should the thermostat go in an open-plan room?

Put it where people spend time, away from the kitchen end. In a kitchen-diner-living space, the cooker, oven, dishwasher and fridge all add heat. A thermostat by the hob reads warm and leaves the sofa end cold.

• Choose the living or dining end, on an internal wall or the side of a kitchen run that faces the seating, not on the wall behind the hob.
• Avoid the glazing. Bifolds and roof lights bring sun and cold draughts, both of which upset the reading.
• Split large spaces into zones, each with its own loops and thermostat, if the kitchen and living areas have very different heat loss or use.
• Use a remote sensor if there is no good wall. A wired Heatmiser Thimble Sensor or a Heatmiser Wireless Air Sensor reads the room at the right spot, while the thermostat itself sits somewhere tidier. Supported thermostats can average several wireless sensors in a large room.

Where does the thermostat go in a bathroom?

Outside the bathroom, usually on the landing or bedroom wall just outside the door, with a floor probe in the bathroom floor. Electric UFH thermostat instructions say the thermostat must be mounted outside zones 0, 1 and 2, and that it must go in an adjacent room if that is not possible inside the bathroom. Moisture is also a reason in its own right: steam and condensation shorten the life of a standard wall thermostat.

With the thermostat outside, set it to floor sensing so it controls the bathroom by the floor temperature. Heatmiser recommends exactly this for bathrooms. The final electrical connection for electric UFH must be made by a qualified electrician under Part P and BS 7671. Our guide to electric UFH in bathrooms: zones, RCDs and Part P explains the zones in detail.

Where should the floor probe go?

Halfway between two pipe runs or heating cables, about 1m in from the edge of the heated floor, inside a conduit. Heatmiser's fitting advice is clear on each point:

1. Fit the probe in a conduit so it can be pulled out and replaced later without lifting the floor. Seal the tip end so screed or adhesive cannot get in.
2. Place it midway between pipes or cables, never on top of them. A probe touching a pipe reads high and cuts the heating early.
3. Go about 1m into the floor from the edge, so it reads the heated area, not the cooler perimeter.
4. Keep it out from under rugs and furniture. A thick rug or high-tog carpet over the probe changes the reading.
5. Check the probe type. Heatmiser thermostats use a 10K probe as standard. The neoStat V2, neoStat-e V2 and neoStat WiFi can also take 12K or 15K probes, which matters when you reuse an old probe.

When should you use the probe? For electric UFH it is essential: Heatmiser states that air sensing alone must not be used to control electric underfloor heating. For water UFH under engineered wood, vinyl or LVT, use the probe as a floor limit to protect the finish. On the neoStat-e the floor limit can be set from 20 to 45°C, with 28°C as the default. As a rough starting point, Heatmiser suggests a floor setting about 4°C above the room temperature you want. Our guide to floor probes, air sensing and floor limits goes further.

Should you choose a wired or wireless thermostat for a hard-to-reach wall?

Choose wireless when the best spot has no cable route. A battery thermostat such as the Heatmiser neoAir can go on the ideal wall without chasing plaster, and talks to a UH8-RF wireless wiring centre at the manifold. It is the easy answer in a finished room or a retrofit.

Wired thermostats, such as the Heatmiser neoStat V3, suit new builds and renovations where cables go in before plastering. Either way, the position rules above still apply: a wireless thermostat on a sunny windowsill is no better than a wired one. See neoStat vs neoAir vs Slimline to compare models.

Frequently asked questions

How high should an underfloor heating thermostat be mounted?

About 1.4 to 1.5m from the floor in an existing home. In a new home built to Approved Document M, keep the top of the control no higher than 1200mm, and no lower than 450mm.

Can I put a UFH thermostat on an external wall?

It is best avoided. Outside walls are cooler than the room and can make the heating run on. If there is no other choice, keep it away from windows and doors and seal the back box against draughts.

Can the thermostat go in the bathroom?

Electric UFH thermostats should be outside zones 0, 1 and 2, and makers advise fitting them in the next room if there is no safe spot. The usual layout is a thermostat outside the door with a floor probe in the bathroom floor.

Where should the thermostat go in a kitchen?

Away from the hob, oven, dishwasher and fridge, and out of the sun. In a kitchen-diner, put it at the dining or seating end, or use a remote air sensor there.

Where do I put the floor sensor for underfloor heating?

In a conduit, halfway between two pipes or cables, about 1m in from the edge of the heated floor. Never on top of a pipe or cable, and not under a rug.

Can one thermostat control two rooms?

It can be wired that way, but Part L expects room-by-room temperature control for new systems and replacement heat sources, with only limited exceptions. One thermostat per room or zone is the normal approach.

Why does my thermostat say the room is warm when it feels cold?

The thermostat is probably reading a warm spot: sun on the case, a nearby appliance, a TV or a radiator. Move it, add a remote sensor, or switch to floor sensing with a limit.

Sources: IET: accessory mounting heights (Approved Document M), Heatmiser: thermostat and Thimble Sensor height, Heatmiser: how to install the neoStat, Heatmiser: fitting floor probes, BEAMA: Part L heating controls guidance