Smart Thermostats: How They Work and What They Do

A smart thermostat is an internet-connected thermostat that gives you digital control over your home's central heating¹. Unlike a basic room thermostat, which only senses temperature and switches the boiler on and off, a smart thermostat connects to your Wi-Fi so you can change the heating from a phone, tablet or computer, whether you are on the sofa or away from home². Products in this category let consumers remotely control their home temperature via a smart or remote device such as a tablet, smartphone, PC or laptop³.

The savings on offer are real but modest and not guaranteed. Independent estimates range from around £75 a year with a smart thermostat⁴ to up to £110 a year for a smart thermostat with controls⁵, while industry statistics for full heating control upgrades put the figure at £154 a year for a flat and £484 a year for a detached house⁶. What you actually save depends on your home, your heating habits, the controls you already have, energy prices and how you use the thermostat's features¹.

Most smart thermostats cost between £119 and £219 for the unit, with installation often extra⁷. This page explains what a smart thermostat does, what hardware it needs, which models control hot water, how the main UK brands differ, and where the technology still leaves a household dependent on Wi-Fi, apps and the companies behind them.

Understanding smart thermostats and their operation

A smart thermostat is an internet-connected thermostat that gives you digital control over your home's central heating¹. The "smart" part is the connection: the thermostat links to your home Wi-Fi, which allows it to form part of a more connected home heating system¹. Once connected, it can be programmed or remotely controlled to manage your home's temperature quickly and easily⁸.

The category emerged from earlier remote-control products, defined as products that let consumers remotely control their home temperature via a smart or remote device, such as a tablet, smartphone, PC or laptop³. What separates a smart thermostat from an ordinary programmable one is not just the schedule but the two-way link: the thermostat reports back to an app, and the app can change settings from anywhere. Smart thermostats such as Hive and Nest connect to your Wi-Fi so you can control your heating and hot water through your smartphone, tablet or desktop².

One point of confusion is worth clearing up early: a wireless thermostat is not always smart¹. Wireless refers only to how the thermostat talks to the boiler, by radio rather than a cable. Smart thermostats usually add app control, internet connectivity, automation or other connected features on top¹. A wireless thermostat can be entirely conventional, and a smart thermostat can be wired to the boiler.

A lot of boilers are not Wi-Fi enabled, so many smart or wireless thermostat systems still include a wired element: a receiver or hub that must be wired to the boiler, with the wiring done by a trained professional¹. The wall unit you interact with is only part of the system. The rest of this page covers what that hardware looks like, what the features do, and what a household gives up and gains by moving to app-based control. For the wider picture of thermostats, timers and zoning, see the guide to heating controls.

Features: app control, learning, geofencing and voice assistants

Depending on the model, a smart thermostat may allow you to use app control, voice control, hot water settings, location-based heating, reminders or alerts, open window detection, routine learning, and heating-use tracking¹. Not every model offers every feature, and the list is worth working through because the features, not the label, are what you are paying for.

App control is the foundation. Smart heating controls let you turn the system on or off and change the temperature using your smartphone when you're not at home⁹. Most smart thermostats also allow you to programme in multiple routines, so that your home is always at your desired temperature at the times you choose⁸.

Location-based heating, usually called geofencing, uses your phone's location to decide when to heat. tado°'s feature set includes Geofencing, Open Window Detection, Preheat Before Arrival, Weather Adaptation, Adaptive Heating, Holiday Mode and full Energy IQ insights, with the advanced features bundled under its AI Assist subscription¹⁰. Learning thermostats go further: the Google Nest Learning Thermostat (Gen 3) is described as a modulating and learning thermostat with frost protection, GPS tracking, a motion sensor, program modes and a child lock¹¹. Voice assistants are near-universal at the top of the market: tado° supports voice control via Alexa, Siri or Google¹⁰.

The practical value of these features is that heating follows life rather than a fixed timetable. The main ways a smart thermostat saves money are remote switching off via the phone, more sophisticated sensors that avoid temperature extremes, and heating or pre-heating certain rooms while leaving unused rooms untouched⁸. A quick tap on the phone can save hours of wasted heat and energy⁸. How much that adds up to in pounds is covered below, and the honest answer is that it varies a great deal.

How different models manage your hot water

Whether a smart thermostat can control hot water as well as heating depends entirely on the model¹. This matters most in homes with a regular boiler and a hot water cylinder, where the cylinder needs its own timer and thermostat. In a combi home there is no cylinder, so the question does not arise.

The differences are concrete. The Google Nest Learning Thermostat (Gen 3) can control hot water; the Google Nest Thermostat E cannot¹¹. tado° sells a wireless smart thermostat starter kit with hot water control¹². At the heat pump end, the Passiv Smart Thermostat controls hot water when connected by RS485 Modbus, but with relay control it manages space heating only and not hot water¹³.

The lesson for a buyer is to check the specification for the words "hot water" before ordering, because two models from the same maker can differ. A household that heats water by cylinder loses little by skipping hot water control if the existing cylinder timer is adequate, but a single app that runs both is simpler to live with. For the detail on cylinder controls, see hot water controls.

Typical yearly savings range from £75 to £154, with no guarantee

The headline figures first. The Energy Saving Trust estimates savings of around £75 per year with a smart thermostat⁴. Confused.com puts the figure at up to £110 a year for a smart thermostat and controls used to fine-tune heating⁵. Industry statistics from Beama on full heating control upgrades give £154 per year for a flat and £484 per year for a detached house with all controls ticked⁶. For comparison, simply turning the thermostat down one degree, from 22 to 21, saves around £120 a year in Great Britain or £80 in Northern Ireland⁹.

Two things explain the spread. First, the figures measure different things: a single smart thermostat replacing a basic control saves less than a full upgrade of thermostat, programmer and radiator valves together, which is why the detached-house figure is so much higher. Second, the starting point matters. A home going from no timer at all saves more than a home that already has a well-used programmer and thermostatic radiator valves.

Beyond the device itself, controls open a second route to savings: smart tariffs. An Energy Saving Trust report on integrating smart tariffs with low-carbon home technologies found that savings of up to around £800 a year are possible¹⁴, though that figure comes from combining flexible tariffs with technologies such as heat pumps and batteries, not from a thermostat alone. Some guidance also suggests smart thermostats could help save hundreds of pounds a year¹⁵, which is a looser claim than the specific estimates above.

For a household weighing the purchase, the honest framing is this: the device costs £119 to £219⁷ and the mid-range independent estimate is around £75 to £110 a year⁴, so the payback period is plausible but not instant, and only if the features are actually used. The wider evidence on whether controls pay back is examined in do heating controls save money.

Device prices of £119 to £219 plus fitting charges

A smart thermostat unit costs £119 to £219, but some have add-ons such as installation which push the price up⁷. Beyond the headline range, the market stretches in both directions at the time of the independent price readings in September 2026: the tado° V3+ Smart Heating Thermostat Starter Kit was listed at £59.99, the Habi Wireless Smart Thermostat at £62, and the Worcester Bosch EasyControl Smart Thermostat at £170¹².

Those are device prices. If you want a smart thermostat, you may have to pay for the device and the installation², and professional fitting is a separate charge set by the installer, so there is no single published figure for it. Some systems also carry ongoing costs: energy monitors and smart thermostats generally come at an additional cost, with subscription costs for premium services¹⁶. tado° includes remote control via its app, Smart Schedules, smart home and voice assistant integration via Matter, Multi-Room Control, Room Link and step-by-step DIY installation guides with any tado° product at no additional cost¹⁰, while its AI Assist features sit behind a subscription¹⁰. The Passiv Smart Thermostat states there are no ongoing charges and every feature is included for free¹³. The subscription question is covered in more detail in smart thermostat subscriptions.

Make sure your boiler or heat pump is compatible

Before buying a smart thermostat, check that it's compatible with your boiler and heating system; this is usually stated in the product description or on the thermostat manufacturer's website¹. This is the single most common cause of a wasted purchase, because thermostats talk to boilers in different ways, by simple on-off switching or by modulating control, and not every thermostat supports every boiler.

The makers' own compatibility claims give a sense of the ground covered. tado° works with the heating systems already installed in most homes and is available for setups with wired or wireless thermostats¹⁰. Netatmo's wireless products work with modern combi boilers¹⁷. At the heat pump end, the Passiv Smart Thermostat can control a heat pump via RS485 Modbus or relay, and control via relay is possible with all heat pump makes and models¹³.

Scheme rules show how seriously compatibility is treated. Under ECO4 Innovation, the Homely Smart Thermostat must only be installed where the homeowner already has a Wi-Fi connection¹⁸, and smart thermostats appear as an approved measure type, Smarttherm, in the ECO4 measures table¹⁹. If your home has a heat pump, or an older or unusual boiler, confirm support in writing before ordering, and see smart thermostat boiler compatibility for the detail.

Choosing between wired, wireless and radiator valves

A smart thermostat system has two parts: the control you touch or tap, and the receiver or hub that talks to the boiler. A lot of boilers aren't Wi-Fi enabled, so many smart or wireless thermostat systems still include a wired element, and that wiring should be done by a trained professional¹. The choice between wired and wireless is therefore about where the wall unit goes, not whether any wiring happens at all.

tado°'s smart thermostat is available in wired and wireless versions, with a wireless booster available to allow the device to keep its connection at range²⁰. The distinction matters in larger homes, where a wireless link between the thermostat and the receiver saves running a cable through the house, and in replacements, where a wireless unit can go where the old thermostat was without new chases in the wall.

The third option extends control to individual radiators. Some models of programmable thermostatic radiator valves can be connected via Wi-Fi to smart heating controls, letting you create a new zone for each room⁹. That turns a single-temperature system into a room-by-room one, which is where the larger savings figures for full control upgrades come from⁶. The trade-off is cost and complexity: each radiator needs its own smart valve, and each valve is another battery-powered device to maintain. The detail is in smart TRVs and in the comparison of smart TRVs and a smart thermostat.

Fitting: the installer and the right location

Who should fit one depends on the brand and on the wiring involved. Hive recommends that you find a local tradesperson to install your smart thermostat, as it can be a bit of a task if you are not confident²⁰, and Which? records that Hive recommends professional installation of its smart thermostats¹¹. The Google Nest Learning Thermostat (Gen 3) carries a professional installation recommendation, while the Nest Thermostat E is listed for self or professional installation¹¹. The Passiv Smart Thermostat requires professional installation¹³. Because the receiver or hub must be wired to the boiler and that wiring should be done by a trained professional¹, most homes will use an installer for at least the boiler end of the job.

Placement is simpler than with a conventional thermostat but the same rule applies: the best place to put a smart thermostat is in a place where the temperature is relatively consistent⁷. That means avoiding direct sunlight, draughts and direct heat from radiators or cookers, so the sensor reads the room rather than a hot or cold spot.

Timing is worth a thought too. The best piece of advice is to look into replacing your old thermostat before it gets too cold⁸: installers are busiest once the heating season starts. A household planning a DIY fit should also read whether DIY installation affects a boiler warranty, and the general process is set out in installing and replacing heating controls.

Passiv Smart Thermostat: offline heat pump management

The Passiv Smart Thermostat is a distinct proposition aimed at heat pump homes, and its maker's claims should be read as maker claims. It makes comfort simple while reducing energy bills by up to 30%, optimising heat pumps according to the weather and energy prices¹³. Control via RS485 Modbus is possible with many leading heat pump brands and delivers the best level of bill savings, including an efficiency gain of 17% for the heat pump¹³. Control via relay is possible with all heat pump makes and models, but with relay control the thermostat manages space heating only, not hot water¹³.

What sets it apart is independence from the internet. Unlike other smart thermostats, the Passiv Smart Thermostat provides full control of heating and hot water without a smartphone or internet connection, and the system can be commissioned from the Passiv Programmer in under two minutes without the need for a smartphone or internet connection¹³. For a household whose priority is that heating keeps working when broadband does not, that is the whole argument.

Practicalities: professional installation is required, the product is available from plumbers' merchants and renewable distributors across the UK, and the maker offers free installation training at its Newbury head office, at installers' premises, or remotely via video call¹³. There are no ongoing charges; every feature is included for free¹³, and a Heat Pump Ready programme project record notes there is no service fee²¹. For a heat pump household comparing options, see also Homely heat pump controls and Havenwise heat pump controls.

UK brands including tado°

The UK market has a handful of established names, each with a different emphasis. tado°'s range works with the heating systems already installed in most homes, comes in wired and wireless versions, and integrates with smart home systems via Matter and smart speakers¹⁰. Included with any tado° product at no additional cost are remote control via the app, Smart Schedules, full smart home and voice assistant integration via Matter, Multi-Room Control, Room Link and step-by-step DIY installation guides¹⁰. Its AI Assist subscription adds Geofencing, Open Window Detection, Preheat Before Arrival, Weather Adaptation, Adaptive Heating, Holiday Mode and full Energy IQ insights¹⁰. From 2 September 2026, the tado° Energy Savings Promise applies to all tado° X heating products purchased on or after that date¹⁰.

Google Nest offers two distinct models. The Nest Learning Thermostat (Gen 3) is a modulating and learning thermostat that can control hot water, with frost protection, GPS tracking, a motion sensor, program modes and a child lock, and professional installation is recommended¹¹. The Nest Thermostat E is also a modulating and learning thermostat with frost protection, GPS tracking, a motion sensor, program modes and a child lock, but it has no hot water control and is listed for self or professional installation¹¹.

Hive recommends professional installation of its smart thermostats¹¹, and its app-based system is one of the most widely installed in the UK. Worcester Bosch's EasyControl Smart Thermostat was listed at £170¹², and the Habi Wireless Smart Thermostat at £62¹², showing how far device prices now stretch. Netatmo's wireless products work with modern combi boilers¹⁷, and its Smart Thermostat requires a Wi-Fi connection to work¹⁷. Which? tests smart thermostats in a temperature-controlled chamber, measuring how accurately they record the temperature and how quickly the relay responds¹², which is the kind of independent testing worth looking for before choosing. Brand-by-brand detail is in the pages on tado°, Hive, Google Nest and Netatmo.

What still relies on Wi-Fi, apps and the supplier

A smart thermostat reduces dependence on wasted fuel but adds dependence on other things, and a household should be clear-eyed about the swap. The thermostat needs home Wi-Fi for its connected features¹, and some models state a Wi-Fi connection as a requirement¹⁷. If broadband drops, the schedule usually keeps running but remote control, geofencing and app-based changes stop until it returns. The features that save the most money, such as location-based heating and remote switching off⁸, are the ones that need the connection most.

The app and its maker are a second dependence. Features sit behind subscriptions for some brands¹⁶, and a maker can change what the app does, what it charges for, or how long it supports a given model. The security and data side of smart heating controls and the question of cloud dependence are covered in full elsewhere on this site.

What a smart thermostat does not lock you into is your energy deal. The thermostat helps to control how much energy you use, but won't be a barrier to switching your actual energy deal⁷. If the household also has a smart meter, cross-compatible SMETS2 meters keep their smart functions across all energy suppliers, using the purpose-built national network, and are now the meter type for any new smart meter installation²²; the Energy Ombudsman confirms a smart meter will keep its smart functions across all energy suppliers, so if you switch supplier the meter carries on working²². Consumers can switch easily and quickly between energy suppliers without any disruption to smart service²³, and SMETS2 meters allow seamless switching because they are connected to a nationwide secure smart meter network²⁴. A smart thermostat, in short, is a tool for using less, not a contract.

Free Nest thermostats in Wales via ECO schemes

Depending on where you live and your circumstances, a smart thermostat or a wider heating upgrade can come free through a scheme. In Wales, the Warm Homes Nest scheme is the main route. The Welsh Government offers free energy upgrades through the Warm Homes Nest Scheme for houses with a poor Energy Performance Certificate (EPC) rating²⁵, and the scheme makes Welsh homes warmer and more energy efficient places to live²⁶. Nest provides free, impartial energy advice to help you lower your energy bills and improve your health and wellbeing²⁷, and free expert energy advice is available to all householders in Wales via the Nest helpline²⁸.

What Nest funds goes beyond advice for eligible households: replacement of a boiler or electric storage heaters to ensure you have a safe and reliable heating system²⁹, and eligible households can get free energy advice and a suite of home energy efficiency improvements³⁰. The Welsh Government describes the scheme as offering free energy efficiency advice and improvements to low-income Welsh households³¹.

In Great Britain, the ECO scheme is the equivalent route. Smart thermostats appear in the ECO4 measures table as the measure type Smarttherm¹⁹, meaning they can be funded through the scheme where a household and property qualify, and ECO4 Innovation has approved measures such as the Homely Smart Thermostat, which must only be installed where the homeowner already has a Wi-Fi connection¹⁸. Eligibility in every case depends on circumstances such as benefits received and the property's energy rating, so the practical first step is the Nest helpline in Wales or an ECO supplier survey in England and Scotland. For the rules around rented homes, see heating controls in rented and social housing.