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2 December 2021

How to buy the best smart thermostat

Our expert buying advice: find out whether you could save with a smart thermostat and which is the right one for your home
Sam Morris
Smart thermostat communicating with boiler via smartphone

Smart thermostats offer greater flexibility then other heating controls, allowing you to remotely control your home's temperature and heating schedule. 

They also have a wide range of different features, so you'll need to decide which ones you need the most. 

Keep reading for our expert buying advice. Or go to straight our smart thermostat reviews to compare and find the right one for your home.

Video: how to buy the best smart thermostat

Why buy a smart thermostat?

Like other boiler controllers, a smart thermostat allows you to schedule your heating, with the aim of saving you money on your heating bills and reducing your boiler's environmental impact.

With a smart thermostat, you can control your heating remotely via the internet, using either an app on your smartphone or a webpage. For example, you could turn your heating on when you're on your way back from a weekend away. Or, if you've had to pop out unexpectedly and realised you've accidently left your heating on, you could turn it off using your phone. 

Like a smart meter, most smart thermostats can show you how much heating you're using – letting you keep a closer eye on your heating bills. 

Some smart thermostats also monitor how you heat your home and learn your routine, allowing you a more hands-off approach to scheduling your heating. 

There are several brands of smart heating thermostats on the market and each works in a slightly different way. Take a look at our Best Buy smart thermostats to see which ones are accurate and have user-friendly apps. 

The smart thermostat features to look out for

Compared with other boiler controls, smart thermostats often have many cost/fuel saving features built into the one device. Although not every smart thermostat is the same, so knowing what the common features are, and which ones you want, can really help to narrow down your search for the best.

All our smart thermostat reviews highlight if they have these common features. 

Hot water control

Some smart thermostats can be used to control your hot water, as well as your central heating. Being able to use an app makes turning on the hot water much more convenient. If you've switched it off because you've had a weekend away, for instance, and fancy a nice hot shower when you get back, simply use your smartphone to turn it on again before you get home. 

Not all smart thermostats with hot water control include it as standard, though, and some charge you extra for it.

If you have a combination boiler, which provides hot water instantly when you turn on the hot tap or the shower, then you won't need a smart thermostat that does this.

Best thermostat for hot water control

  • 75%

    This smart thermostat has great features, it's easy to use and it's incredibly accurate. But did it perform well enough to get a Best Buy recommendation?

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App and PC functionality

Many smart thermostats can only be controlled by an app and don't have a standard website that can be accessed from a laptop or desktop computer. 

If you don't have a smartphone, you'll need to pick a thermostat that also has website control functionality. 

Multi-room control or zonal heating

Some smart thermostats let you set different temperatures in different parts of your home from the same smartphone app. This would be particularly useful if you have a larger property and where parts of it often aren't being used while people are elsewhere.

For example, if you have a dedicated office room, you can heat it during work hours and them turn the heating off in that room after you clock off.

Or, if you usually watch TV in the evening, you can keep your living room nice and cosy while you turn the heating down or even off in any rooms you're not using. 

To use this feature, you'll need a thermostat that supports zonal heating and you will have to buy either an extra thermostat or another connected device such as a smart radiator valve. With two thermostats you could have different settings upstairs and downstairs. With smart radiator valves, you can control each rooms temperature and schedule individually. 

The extra devices are often not cheap, though. Some cost as much as the first thermostat you buy. You'll need to weigh that cost against the potential energy bill savings you could make by not heating parts of your home that don't need heating.

If this is a feature you want, read our smart radiator valve reviews to find the best brand to set up for multi-room heating.

Best thermostat for zonal heating

  • 70%

    The Honeywell Evohome wi-fi connected thermostat pack can create and individually control 12 individual heating zones. It's claimed to be easy to use and suitable for all boilers. We sent this smart thermostat to our test lab to see how easy it is to install, how accurate the thermostat is and whether it keeps your data secure. Read our full review for our verdict.

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Some smart thermostats claim to be able to learn your routine and preferred temperatures, and program themselves accordingly. 

This saves you the trouble of having to program a schedule yourself, potentially offering you savings without you having to do much extra work. But it does reduce the amount of control you have over your heating.

However, learning functions can be turned off. So if you don't like the schedule the smart thermostat has come up with, you can switch back to manual control and program it yourself.

Best smart thermostat for learning

  • 74%

    Launched in 2017, The Google Nest Smart Thermostat E is claimed to help save you energy and to be very easy to install, adjust and schedule. We sent it off to our lab to see how accurately it maintains the temperature, how easy it is to use and whether it keeps your data secure. Read our full review to find out.

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Motion sensors and GPS tracking

The purpose of both of these features is to detect when you enter and leave the your home and adjust your heat settings accordingly, turning the heating down when you've left, and pre-heating your home when you're on your way back.

Some smart thermostats use it slightly differently. For example the Hive's geolocation feature alerts you when you’ve left the heating on and you’re away from home, or when you’re coming back and the temperature’s set lower than you’d like. But it won’t adjust the settings automatically.

This feature is most useful if you're in and out of your home at irregular times, as otherwise you can just rely on the schedule.

Best thermostat for GPS tracking

  • 71%

    This is a very good smart thermostat that we're happy to recommend. Although the app can be confusing, it's easy to control the device manually or through the web portal. It also reads temperature accurately and is easy to install.

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Weather-responsive fuctionality

Smart thermostats with a weather-responsive function can adjust the internal temperature according to the forecast and the temperature outside. 

So if a cold snap is on the way or the sun is about to come out, the thermostat can raise or lower the temperature settings respectively to reflect the fact that the temperature is about to change.

Professional installation

Many smart thermostats require professional installation, which can add significantly to the cost. But some, such as the Tado V3+ smart thermostat or the Netatmo thermostat, can be installed by a competent DIYer.

Check out our smart thermostat reviews to find out which smart thermostats have the features we've talked about here

Is it worth getting a smart thermostat?

If you don't already have a boiler controller installed, then you should definitely consider getting a smart thermostat, as you're likely to save money on your heating bills.

For those who already have a boiler control (like a thermostat or timer), then there are several factors to consider when deciding whether installing a smart thermostat will be worth it. This includes which brand you choose to install, how will you take advantage of the different features it offers and if it will actually save your further money on your heating bills.

What are the pros of a smart thermostat?

  • You can control your heating remotely Through your smartphone, you can control your heating from anywhere in the world, offering greater control and flexibility than other boiler controls.
  • You can see how much heating you're using Most let you view and monitor how much energy you're using, making it easier to see where you could save money.
  • You can create multiple heating zones. Using multiple smart thermostats, or a smart thermostat with smart radiator valves, you can control the temperature on a room-by-room basis and make further energy savings.
  • It can learn your routine to automate your heating Some will learn your routine (such as when you're out of the house or when you go to bed) and can automatically adjust the temperature for you. This means after a week or so after installation, you could start saving on your bills and use less fossil fuels without having to think about your heating again.
  • Voice control If you have Alexa, Apple HomeKit or Google Home and want to integrate your home heating into your smart home setup, get a smart thermostat that works with your device.

What are the cons of a smart thermostat? 

  • Price Although they are coming down in price, smart thermostats generally cost more than non-smart heating controls. This goes up even more if you're also getting smart radiator valves. It will take time to recoup this extra upfront cost through saving on heating bills.
  • Locked into a brand Most smart thermostats are only compatible with that brand's other connected heating devices such as smart radiator valves. If you think you'll want to add smart radiator valves in the future, you'll most likely be locked into the smart thermostat brand that you buy. 

If you're less tech-savvy, or not a confident smartphone user, a smart thermostat will be a bit of a learning curve in order to get the most out it. You can make this easier by getting an engineer to install the thermostat and help set up the schedule for you, or going for one that can learn your routine.

Be aware that a smart thermostat doesn't solve underlying lifestyle choices or poor property insulation issues. While a learning thermostat can help, if you're likely to forget to use the app, or want your heating on full blast all the time, then you're unlikely to save money with a smart thermostat. Similarly, if you have a poorly insulated property it may be better to improve the energy efficiency of your home first.

How do smart radiator valves work? Read our expert guide to see if adding these to your heating system is the right call for you

Will a smart thermostat save you money?

Many smart thermostat manufacturers claim big savings on your energy use and heating bills after installation.

For instance, Tado says you can 'reduce you energy consumption by 31%', while British Gas claim its Hive smart thermostat 'could save you up to £110  a year on your heating bill'.

But the amount you can actually save depends on several factors, including how you currently use your heating. If you already have heating controls, and already monitor how much energy you're using, you'll probably save less switching to smart heating.

Company savings estimates make several assumptions, such as how much energy you use (for example, the British Gas estimate above assumes an annual usage of 16,489 kWh) and that you left your heating set to maintain a constant temperature during the day. 

So if you already turn off the heating when you leave your home, you're unlikely to save as much as the manufacturer's claim.

In short, be wary of the big headline savings claims made by smart thermostat companies. Unless you're in the habit of leaving the heating on while you're out of your home, the savings you make aren't going to be large enough to save you hundreds of pounds a year.

Who will save more with a smart thermostat?

  • Those who want to make a lifestyle change A smart thermostat lets you see exactly how much you're spending, and some even suggest where you can save, empowering you to make those changes.
  • Those comfortable using smartphone apps If you're tech-savvy, you'll get the most out of the different energy-saving features a smart thermostat offers.
  • Those with a busy, irregular lifestyle It will let you control your heating remotely, making sure the boiler isn't on when you're out and letting you adjust the schedule on the go.
  • Those who are likely to stay in the same property for several years You'll recoup the cost of installation through savings on your heating bill.

 Who will save less with a smart thermostat?

  • Those who won't use the smart features If you're forgetful and, for instance, likely to forget to use the app to remotely switch their heating on or off.
  • Those who already use heating controls well Getting a smart thermostat as well could offer further savings, but if you already use a timer to schedule your heating you'll save less than someone who doesn't.
  • Those less confident with using smartphone apps Alhough you can opt for a learning thermostat, such as Nest, that can remember your routine.
  • Those with a poorly insulated home Installing loft insulation or double glazing will improve the energy efficiency of the property, offering greater savings than by just installing a smart thermostat. Find out how to buy double glazing and how much loft insulation costs.
  • Those planning to move property in the next couple of years You may not have time to recoup the higher initial costs of a smart thermostat. 

Is a smart thermostat better for the environment?

In short, yes. Smart thermostats enable you to reduce the amount of energy you use. If yours runs on fossil fuel, such as a gas or oil boiler, it will reduce your carbon emissions, heating your home in a more environmentally friendly manner.

However, like any tool, it's how you use it. If you leave your heating on when not in the house, or have the thermostat set to 30°C all day, then there is still room for you to use your smart thermostat in a more sustainable fashion.

Here are some tips from the Energy Savings Trust to the best way to reduce your carbon emissions with your smart thermostat.

  1. Turn the thermostat down, for every degree you turn your thermostat down, you can save around £55 a year and reduce your carbon footprint by 300kg.
  2. Set your thermostatic radiator valves to the best temperature for each room. This is typically 3 to 4 for most, or 18 to 21°C for smart radiator valves.
  3. Turn the heating off when not in your home, or on frost protection mode (about 7°C) in winter if you're away for a while and there's a possibility of freezing.
  4. Don't turn the thermostat up to try and heat your home quicker. Turning the thermostat up doesn't heat it faster – it will just keep the heating on for longer and waste more energy and cost more money.

Heat pumps advice If you're looking to replace your boiler with a more environmentally friendly option, see if this low-carbon alternative is right for you

Can you have a smart thermostat if you're renting?

Yes, but you should always seek the landlord's permission before installing a smart thermostat in a rented property, and in this situation get a professional engineer to carry out the installation.

There are other factors to consider before installing a smart thermostat if you rent:

  1. Will you make your money back? Unless the landlord pays for the installation, you'll lose money if you pay to install a smart thermostat and then aren't in the property long enough to recoup your costs through savings on your heating.
  2. Can you easily reset the smart thermostat? If you leave, you won't want the next tenants to be able to access your account or data. So make sure the smart thermostat you install can be easily reset and you can delete your account from the smartphone app. 

What to do with your smart thermostat if you move home

When you move home, you can either take your smart thermostat with you or leave it behind.

In all our smart thermostat reviews, we test how easy it is to reset the device and how easy it is to remove the device from your app account. We then also check if a new user connects to the smart thermostat, that they can't see a previous users information or data. 

This means you can be confident (whether you keep or leave your smart thermostat) that the next tenant or homeowner can't access your information, and conversely if you move into a property with a smart thermostat, that the previous owners can't log in a tinker with your heating schedule.  

Taking your smart thermostat with you if you move home

  1. Check that your new home's heating system is compatible with your smart thermostat If it isn't, it will probably easier to leave it behind, then buy and install a new compatible smart thermostat in your new property.
  2. Reset the smart thermostat Some devices have dedicated buttons or come with clear instructions on how to reset the thermostat, while others you have to restart the setup process.
  3. Remove the thermostat from the app
  4. Uninstall your smart thermostat and re-install it in your new home In general, you should have this done by a professional installer, unless you're a competent DIYer and the thermostat states that it can be self-installed, with clear instructions on installing and uninstalling.
  5. Add your smart thermostat back to the app For some, learning smart thermostat apps (such as Nest) you may need to select a new home in the app, so it knows the thermostat is connected to a new heating system and can re-learn your schedule.

Leaving your smart thermostat behind if you move home

  1. Remove the thermostat from the app
  2. Reset the smart thermostat Some devices have dedicated buttons or come with clear instructions on how to reset the thermostat, while others you have to restart the setup process.
  3. If needed, delete your account If you aren't going to be using the app with a device in your new home, it's best to delete your account. For some brands you can do this from the app, but for others visit the website or contact the manufacturer to do this.

Getting a smart thermostat professionally installed

While some smart thermostats describe themselves as being able to 'self-installed', our tests have found that some don't have clear enough instructions or diagrams for this to be the case. Unless you're a component DIYer, or if the smart thermostat instructions don't say it can be self-installed, we would recommend getting a professional electrician to do it.

A Which? Trusted Trader will be reliable and trustworthy. All traders have passed our assessment process carried out by our trading standards professionals. Use the tool to find a professional electrician in your area. 

How we test smart thermostats As well as ease of decommissioning, see how else we put smart thermostats through their paces

Tables last updated 2 December 2021.