Best Buys › Smart Thermostats

Smart Thermostats

The fastest payback of any smart device — provided the thermostat can actually talk to your boiler.

Pen-and-ink drawing of a smart thermostat on a living-room wall

Heating is the largest energy load in most European homes, which makes the thermostat the one smart device with a genuinely short payback period. Everything else on this site is convenience with a side of saving; this is saving with a side of convenience.

Before comparing features, establish one thing: how your heating wants to be controlled. If you have a modern condensing boiler, it almost certainly speaks OpenTherm — a European standard that lets a thermostat and boiler exchange real numbers rather than just an on/off signal. That enables modulating control, where the boiler runs continuously at a low flame instead of blasting to full output and cutting out. Modulation is where most of the efficiency gain lives, and a thermostat that only offers on/off relay control cannot deliver it no matter how clever its app is.

The second question is scope. A single thermostat controls the whole house from one room, which is fine in a flat and poor in a three-storey house where the hallway is always the warmest spot. Room-by-room control needs TRVs (thermostatic radiator valves) — motorised valve heads on individual radiators — so check whether the system you are buying accepts them before committing.

What to look for

OpenTherm or relay

OpenTherm allows modulating control and is what you want with a modern condensing boiler. Simple relay (on/off) control suits older boilers, electric heating and underfloor systems. Getting this wrong is the difference between a thermostat that saves money and one that just looks nice.

What is actually heating your home

Gas combi boiler, system boiler with a hot water tank, heat pump, electric underfloor, water underfloor, or district heating all want different hardware. Several models here handle only one or two of these.

Room-by-room, or one room

If you want per-room temperatures you need a system that supports TRVs, and you need to buy one per radiator. Check the thermostat is “TRV extendable” before you start.

Wired or wireless

Wired units replace the existing thermostat on its existing cable and are more reliable. Wireless units use a receiver box wired at the boiler and a battery unit you can put anywhere, which is easier to retrofit but adds a radio link to fail.

Subscription creep

Several brands put the genuinely useful features — energy reporting, geofencing, open-window detection — behind a monthly plan. Check what the free tier actually includes rather than what the box promises.

Adjustment resolution

Some thermostats only move in 0.5 °C steps. In a well-insulated house that is a noticeable jump; 0.1 °C control is more comfortable and more efficient.

The shortlist compared

BrandModelProtocolControlTRVsInstallIndicative price
tado°Smart Thermostat XMatter over ThreadOpenTherm or relayYesWired€135
NetatmoSmart Modulating ThermostatWi-FiOpenTherm modulatingYesWireless€160
PlugwiseAnnaWi-Fi / LANOpenThermYesWired + gateway€165
Google NestLearning ThermostatWi-FiOpenTherm via Heat LinkNoWireless€249
Google NestThermostat EWi-FiOpenThermNoWireless€219
Honeywell HomeT6Wi-FiOpenThermNoWired retrofit€180
AqaraFloor Heating Thermostat W500Matter over ThreadRelay, 16 ANoWired€70
MerossMTS215Matter over Wi-FiRelayNoWired€78
HeatitZ-TRM3Z-WaveRelay, electric heatingNoWired€120
SwitchBotHome Climate PanelBluetooth (hub required)Drives SwitchBot TRVsYesWireless€50
EcobeePremiumWi-Fi24 VAC, needs a C wireNoWiredUS / Canada only

Prices move constantly and vary by country, so we give an indicative band rather than a figure that would be stale within a month. Check the brand's own store for the current price.

The picks in detail

tado° Smart Thermostat X

Matter over Thread

The X generation moved tado° onto Matter over Thread, which quietly removes the need for their Bridge X if your hub already acts as a Thread border router — the device that connects a Thread mesh to your home network. That makes it the cleanest integration in this list, and the ecosystem around it (Radiator Thermostat X valve heads, Heat Pump Optimizer X, wireless temperature sensors) is the most complete.

Be clear-eyed about the subscription. The hardware works fully without one, but energy reporting and “auto-assist” features like geofencing and open-window detection sit behind a monthly plan. If those are the reason you are buying, factor in the running cost.

  • Supports both OpenTherm and relay control
  • Full ecosystem of TRVs, heat-pump optimiser and remote sensors
  • Needs no tado° bridge if your hub is a Thread border router
  • Slim 21 mm profile
  • Energy metering and auto-assist are subscription-only

Netatmo Smart Modulating Thermostat

Wi-Fi

If your boiler modulates, this is the purpose-built choice. It handles both space heating and domestic hot water — your tap water — provided the boiler has a hot water tank, which few competitors manage. Auto-Adapt factors in outdoor temperature and how quickly your house loses heat to decide when to start.

The e-paper screen is a genuinely good decision: readable from across the room at any angle, and it costs almost no power, so the AAA cells last around two years.

  • Built specifically for OpenTherm modulating boilers
  • Also controls domestic hot water
  • Auto-Adapt uses outdoor temperature and your home’s insulation
  • E-paper display readable from any angle
  • Only adjusts in 0.5 °C steps

Plugwise Anna

Wi-Fi or LAN

The Dutch pick, and the most precise: 0.1 °C steps rather than 0.5, which in a well-insulated house is the difference between comfortable and slightly-too-warm. Unusually it can also control a district-heating main valve, which matters in Dutch and Scandinavian apartment blocks where there is no boiler to talk to at all.

It ships with the Smile-T gateway, a separate box wired to the boiler that joins your network over Wi-Fi or Ethernet. That is one more thing on a shelf, but it also means the connection to the boiler is not dependent on Wi-Fi reaching the hallway.

  • Finest resolution here at 0.1 °C
  • Works with boilers, hybrid heat pumps and district heating
  • Humidity and light sensors usable in automations
  • Ethernet option for a stable connection
  • Requires the Smile-T gateway
  • Two-colour screen is hard to read at a distance

Google Nest Learning Thermostat

Wi-Fi

Still the most attractive thermostat you can buy, and the learning algorithm is not marketing — it does build a reasonable schedule from how you actually behave. Sensors for temperature, humidity, light, occupancy and proximity mean it wakes up as you walk past.

The limitation is architectural: there is no TRV ecosystem, so you get one temperature for the whole house. In a flat that is fine. In a house with cold bedrooms it is a real constraint, and the cheaper Thermostat E offers the same sensors and learning in a plainer body.

  • Excellent sensor set including occupancy and proximity
  • Genuinely effective schedule learning
  • Best-looking unit here by some distance
  • Most expensive on the list
  • No TRV support, so no room-by-room control

Aqara Floor Heating Thermostat W500

Matter over Thread

A specialist, and the right answer if you have electric underfloor heating rather than radiators. It switches up to 16 A / 3680 W and uses an external NTC sensor — a thermistor probe embedded in the floor — to regulate floor temperature rather than air temperature, which is how underfloor systems are supposed to be controlled. It also acts as a Thread router.

  • Purpose-built for electric underfloor heating up to 16 A
  • External floor probe included
  • Native Matter over Thread with no Aqara hub
  • Energy monitoring
  • The Matter interface currently exposes fewer settings than Zigbee

Heatit Z-TRM3

Z-Wave

A Scandinavian workhorse for electric heating — underfloor, panel heaters, infrared. No learning algorithms, no app theatre, just a solid Z-Wave thermostat with metering that reports into your energy dashboard. It is mains-wired into the wall box, so unless you are confident with fixed wiring this is an electrician’s job.

  • Cheap, minimal and very reliable
  • Two additional wired external sensors possible
  • Energy metering
  • Child lock and adjustable backlight
  • Mains wiring usually needs an electrician
  • Electric heating only

SwitchBot Home Climate Panel

Bluetooth, SwitchBot hub required

An interesting outlier: not a boiler thermostat at all, but a wall panel that commands SwitchBot radiator valve heads directly and treats a group of them as one zone. For a rented flat with radiators and no permission to touch the boiler, it is the cheapest legitimate route to per-room heating. You will need a SwitchBot hub in the chain.

  • Cheapest route to room-by-room control
  • Combines thermometer, presence sensor, controller and buttons
  • Syncs several TRVs as one zone
  • Requires a SwitchBot hub to reach your smart home system
  • Only drives SwitchBot valve heads

A note on North American models

Ecobee’s thermostats are excellent and repeatedly top US reviews, but they are built for North American wiring: 24 VAC low-voltage control with a C wire (a dedicated “common” conductor that supplies continuous power to the thermostat). European homes almost never have either, because our heating is controlled by mains-voltage switching or OpenTherm instead. Sold in the US and Canada only, and not a realistic option elsewhere — which is why it sits at the bottom of the table rather than being ruled out on merit.

Check compatibility with your specific boiler before buying anything. Most manufacturers publish a compatibility checker, and the answer depends on the exact model and how it was installed, not just the brand. A thermostat that cannot modulate on a modulating boiler will still work — it will simply throw away most of the saving you bought it for.

Further reading

Frequently asked questions

What is OpenTherm and do I need it?

OpenTherm is a European standard that lets a thermostat and boiler exchange actual values rather than a simple on/off signal. It enables modulating control, where the boiler runs continuously at a low output instead of cycling between full blast and off. If you have a modern condensing boiler, OpenTherm is where most of the energy saving comes from and is worth insisting on.

What is the difference between modulating and on/off control?

On/off (relay) control switches the boiler fully on until the room is warm, then fully off. Modulating control varies the flame continuously to match demand, which keeps the boiler in its efficient condensing range and avoids temperature swings. Modulating needs both a compatible boiler and a thermostat that supports it.

Do I need TRVs as well as a thermostat?

Only if you want different temperatures in different rooms. One thermostat measures one room and heats the whole house to suit it, which is fine in a flat and poor in a multi-storey house. TRVs are motorised radiator valve heads that let each room hold its own target — but you need one per radiator, so the cost adds up quickly.

Will a smart thermostat work with a heat pump?

Some will, but not all, and the wrong one can make a heat pump less efficient by short-cycling it. Heat pumps prefer long, steady, low-temperature runs, so look for models that explicitly support heat pumps — tado° sells a dedicated Heat Pump Optimizer, and Honeywell’s T6 and Plugwise’s Anna both handle hybrid systems.

Are the subscriptions necessary?

No thermostat here stops working without one, but tado° and Ecobee both put desirable features behind a plan — energy reporting, geofencing and open-window detection in tado°’s case. Netatmo, Plugwise, Heatit, Aqara and Meross have no subscription at all, which is worth weighing over a five-year life.

Terms explained

OpenTherm
A European communication standard between thermostats and boilers that allows continuous, modulating control rather than simple on/off switching. Both the boiler and the thermostat must support it.
Modulating control
Varying a boiler’s output continuously to match demand, instead of cycling between full power and off. It keeps a condensing boiler in its efficient range and gives steadier room temperatures.
TRV (thermostatic radiator valve)
A valve head fitted to an individual radiator. Smart versions are motorised and let each room hold its own target temperature, which is the only way to get true room-by-room zoning with radiators.
Thread border router
A device that connects a low-power Thread mesh to your normal home network. Most modern smart home hubs act as one, which is why several Thread thermostats no longer need the manufacturer’s own bridge.
C wire
A dedicated “common” conductor in North American 24 VAC heating wiring that supplies constant power to the thermostat. European systems do not use it, which is why several US thermostats cannot be installed in Europe.

More terms in the smart home glossary. Related questions: What is a C-wire, and why does my thermostat need one? What is OpenTherm?