/ Home & Energy, Money

For and against smart thermostats

Cat on radiator

Smart thermostats are the latest trend in home heating. But do they really help to heat our homes more efficiently? Two Which? staffers put them to the test…

Lisa Barber says:

Lisa BarberYou might think that getting a smart thermostat – which controls your heating from an app on your phone – would cause your energy bills to rise. After all, surely it’s far too tempting to keep yourself cosy by turning up the heating from the comfort of your duvet or sofa?

However, I find I actually spend my time turning my heating down. As I haven’t got to fiddle with the overly complicated control panel on the old thermostat, I’m much more likely to keep on top of making sure we only use the heating when we really need it.

Plus, my smart thermostat lets me control individual radiators. This means that when I’m in front of the TV of an evening I can spend a minute switching off radiators in any rooms I’m not using.

Being able to see the temperature in individual rooms is rather handy, too. It’s much easier to demand that your family put jumpers on if you know it’s already over 20°C. Whereas with our old thermostat, which lived in our draughty hallway, we never really knew what the temperature was and whoever was coldest would usually sneakily turn up the dial.

So for me, having a smart thermostat has definitely reduced the amount of energy I use.

Amy Hupe says:

Amy HupeI was tempted into getting a smart thermostat – not so much to cut my energy bills, but because of the added convenience. That said, I was interested to see if greater control and feedback about my consumption would encourage me to use less – it has not.

I really feel the cold, always seeming to be several degrees chillier than everyone else in the room. The ability to switch my heating on when I leave work, so the house will be cosy as soon as I walk in the front door, has proved stronger than my desire to reduce my heating bills.

My other half and I both have the app installed on our phones, and when we first had our smart thermostat installed we set out with firm resolve to remember to switch our heating off when we went out for the day at the weekend (when our heating is set to 20°C by default).

Sadly though, with nothing to remind us, we only tend to remember about half the time – the same as when we had a standard thermostat. While I feel motivated to turn my heating on when I’m cold, there’s little to remind me to switch it off when I don’t need it.

All in all, while I think it’s been great for convenience, I’m just not as engaged with my energy use as I am with my comfort, and getting a smart thermostat hasn’t changed that.

What do you think of smart thermostats?

If you already have a smart thermostat, tell us more about it – particularly if it has smart learning, as we want to know more about whether this actually works. If you don’t have a smart thermostat, do you think one would work for you?


We went for the Hive earlier this year and really regret it. I should say they have a new model now, so our experience is based on the old model and I would be interested to know if the new model works any better.

Before the Hive, we left the radiators on 24/7 in the middle of winter. The radiators by the entrance doors were turned up full, the rest turned down to maintain reasonable temperatures in the other rooms i.e. low in the bedrooms, a bit higher in the bathroom and living rooms. The downside to leaving on 24/7 was the boiler kicked in every few minutes whether it was needed or not but we were comfortable. We also had a very handy 1 hour boost for hot water or heating with one press of a button.

So having heard about the Hive we decided to go for it. We now go hot, cold, hot, cold, hot, cold………..

The boiler works nearly non-stop until the temperature is reached then stops but the hot radiators continue to heat the room for a while. Then the radiators go cold before the Hive thinks it needs to start up again and the temperature drops a little more before it starts heating again.

The cold weather is only just starting but we are going to try lowering the radiator in the living room where the Hive thermostat is to see if that will maintain a more comfortable temperature.

All the fancy software around a smart thermostat is not much good when the end product i.e. heating does not work properly. We do seem to be using less gas though.

I see my comment has had 2 thumbs up so must agree with me.

It would be good if those people could give their experiences as I would really like to hear them.

Noel says:
18 October 2015

We have a hive but don’ have the thermostat in the living room. It is in the entrance hall away from any radiators. We set the temperature to 18C so it doesn’t heat the whole house too warm but keeps the living rooms at a nice steady 20-21C. So where you place the thermostat is critical and depends on your house design.

Noel, we thought we would try your suggestion of the front hall. It is the area that heats up and cools down the fastest so the Hive does cut in more often.

By turning the temp down to 16-18C and keeping the hall door shut, the rest of the house is maintaining a better temperature overall.

We are still fiddling with the temperatures but there is an improvement.

I’ve had a nest (US import) since before the UK launch, and replaced it with a ‘proper’ UK nest shortly after – it’s great, the “Auto Away” feature has reduced our gas usage by about 20-30% compared to our previous thermostat. The ability to control the heating when away is great too, making sure the house is warm for when you’re home without needlessly wasting energy when out.

Nest is also quite clever in it’s ability to determine how long heating will take to reach a specific temperature, it learns this so if you ask for the house to be *at* 19ºC for when you wake up, then it will automatically turn the heating on earlier taking into account how long it should take to heat up.

Only negative point I’d have is that the UK version of Nest is very basic compared to the US counterpart, and cannot control air conditioning.

I’ve had a similar experience Ross, the Nest is very good at what it does.

From what I’ve read of it all, Nest led the pack, others followed. Perhaps in some measure better but overall I think you’d struggle to beat the Nest, especially as it can talk to other systems, albeit limited for the time being depending on what’s been written for it software wise.

The auto-away is utterly genius, saves running heating when nobody is in the house and I reckon that’s paid for the Nest and then some over the past year os so alone, probably a couple or few times over.

The best bit is, you don’t need to do anything, just let it work it out for you as you say, it figures stuff out so you don’t have to, it just saves burning heating when it’s not required and has proven extremely effective in that.

And, it’s as easy as easy can be for anyone to operate, even total technophobes.

It’s actually hard to find a downside to it.

Previously I used an X10 based stat and have a Z-Wave one that’s never been installed because Nest launched in the UK. So, I’m no stranger to more “intelligent” control and most are an order of magnitude harder than the Nest is to both install and use.


I don’t have what most people consider a smart thermostat, I have a modern Worcester Bosch thermostat. It monitors the temperature in and outside of the house to automatically adjust the various programmes we have set for our weekday and weekend routines. As such we don’t have to remember anything and we don’t need an app to constantly fiddle with the heating. Set it and forget it but stay warm economically .

I have the hive, and upgraded to the new one, I can say I have loved the new feature of boost, most of the time the heating is off, but if it gets a bit chilly I can press the boost button, from a hour up . and it does the job. I would like the smart thermostats if I thought they would be better than the ones I have , but I have always liked the hive, but I must be honest that I do forget I have the app on my phone, but the settings are easy to set, and it has enabled me to heat my home a lot more efficiently, as the dial on my heating was a waste of time . so we had to have it on full blast to turn it on , but having the hive solved that and now I would not live without it. and I must also say that if I have had a problem, and I have rang the help team, they have sorted it out for me. so for me hive was a great addition to have .

Do you get a constant temperature unlike our experience I described in the first post above?

Jimbo says:
17 October 2015

We have the Honeywell Evohome system and have been running it for 18 months now, and are off grid so have an oil combi boiler. We have found the system fantastic and have reduced our oil consumption by around 20% mostly because of the zoning feature withe the smart radiator TRVs. If you are loooking at these systems you need to differentiate between smart thermostats that have clever radiator valves and those that dont. All have apps you can adjust the timings for have an older house with many rooms but I have heard mixed results about Nest etc – how does it actually know you are not still in the house just because you havent walked past it in an hour or so??

For us the ability to only heat the rooms that are occupied (ie bedrooms in the morning and night) together with the app to switch off the heating when not needed, or boost rooms when required is where the savings and convienience come from.

We use tado, version 1. It has a wall controller sited where the old programmer was and a solar powered mobile thermostat which works around the house. Each of my wife’s and my android smart phones run a tado app which allows control of the system and shows a log of heating over time. The phones also report our positions to the controller so the heating switches off when the last person leaves home. The controls and sensors are not zoned though this now offered.
We’ve had the system for nearly 2 years. For better and worse, I’d say we have been part of its development. The programming system has improved and now meets our needs. One of its great strengths is that once it’s been set up you can just leave it to run, summer and winter. The underlying algorithm is usefully complex taking into account the heating inertia of the house and local weather conditions. For exception needs the program can be overridden either from the wall controller or from either of the phones.
The only problem we have is that the phones don’t always report our home position accurately. I think this is because we are in a weak cellphone signal area.

I have the tado system as well, a recent update give much more flexibility on times and temperatures. The morning temperature and heat up of the house works well and it maintains a good even temperature at other times of the day. One of the reasons for going with tado is that they have an app for a Windows phone, which I have. The only gripe is that my wife’s cheap android phone doesn’t always update it’s location so I sometimes find that the heating’s still on as it thinks she’s at home when she’s not.

I have a pretty good heating automation system but I’ll not mention which so that my comments are not seen to be hidden advertising. Suffice it say that it gives me some experience with which to offer the following opinions:

Firstly some of the comments above highlight one particular issue – namely that being able to remote control your heating whether it be on a whole house basis or individual room might be convenient but eventually you will tire of having to be on top of it all the time and you will forget to do or undo adjustments. This means you could regularly end up using more energy or feeling uncomfortable. I think most people will probably end up in this category. In order to aspire to energy savings without losing comfort you need automation and automation that doesn’t make too many mistakes.

Secondly – the ability to zone your heating is important. A single temperature sensor whether it be on your old hallway thermostat or on a Nest type product will be well outperformed by a system which can regulate individual rooms and particularly so if you have a habit of keeping doors closed.

People tend to base a lot on what the absolute temperature reading is saying but don’t realise that this in itself depends on where you put the sensor (to say nothing of intrinsic sensor accuracy). A 20C measurement next to a wall or near a radiator will not necessarily mean it is 20C where you are sitting, and even if you avoid the obvious ‘next to radiator’ pitfalls you can have all sorts of other influences – some seasonal. So it is probably better if you can just arrive at a temperature setting profile which you feel comfortable with for your particular set up and environment. Humidity and direct sunlight are other factors but I’ll not go into that…

Automation based on geo-location sounds good but is quite crude. Sure it can work for some people under certain conditions but not for others and not at all times. Don’t get caught up by hype – find out exactly how it works and use common sense to decide how often it will be effective for YOU. The propensity for mistakes is high. If these affect you then you may not notice straight away because heating has such a slow dynamic but your bills or comfort will likely suffer over time. BTW even a well known thermostat provider admitted their product was causing increased energy usage earlier this year and rolled out a software update to ‘improve performance’ – I think probably because enough time had passed for things to become more evident… If you have someone at home most of the time then geo-location will count for less (zoning will have far more effect) and the significance of mistakes is likely to incease.

At the end of the day you can always save 100% of your heating bill by simply switching off the heating altogether. You might even imagine that a particular product might deliberately tweak down the actual setting from what the user has demanded – on the basis that they may not notice being a little bit cooler but it will give the product a good energy saving credential – who knows, that might actually be a good idea if it works.. But anyhow lets not lose sight of the point that aside from having some nice gadgetry, the longer term point of having a smart heating system is not just to save you energy but to do so without compromising your comfort.

Like Jimbo, we have the Honeywell Evohome system. It was only installed recently as we have only been in the house 6 months. I will not be able to do comparisons but I like the zone control and smart TRVs. A quick glance at the controller as we go out reminds me to turn it off if we are going to be away. Then I can turn it back on from my phone an hour before we return. This winter will be the test now we have installed double glazing and roof insulation.
From the research I did the Hive didn’t do what I wanted, i.e. no individual room zones, and I didn’t find the Nest.

I have the Evohome the system as well and have found it very good. Another feature I like is the heating comes on early in individual rooms depending on how cold the room is.

For the second Which? reviewer she could just set a location based reminder on her phone so when so is away from home it reminds her to turn off her heating? Sounds like the ones with geo location are a better bet.

I don’t have one of these fancy gizmo’s, but It seems without doubt that nearly everyone is saving energy. If it makes you think energy, then that’s a good thing; but will the cost of purchasing and installing all these different sensors etc actually save any money? Somehow, I doubt it.

I don’t know if I am unusual but I change my room thermostat several times a day. After eating I feel warmer, particularly if I’ve had a glass of wine, and I tend to turn up the heating if I’m tired after a day out. I know where the thermostat is and it shows the room temperature, but I would not like to mess on with a mobile phone to control the heating. Several times a week I play hunt the mobile, which usually turns up in a jacket or trouser pocket or in the door pocket of the car. Maybe there is a smart thermostat operated by a landline. I have four cordless handsets and a wired one, so no playing hunt the phone.

I can see the point of being able to change your thermostat if the house is regularly empty and your hours of return are a bit irregular. However you will need to remember to use your app each time – what would be worse than arriving home on a cold day having forgotten? Or if you had no signal? Brrrrr.

We are more regular and use the programmable controller to make sure the house has heat when we need it. I admit that if we go away for a day or two an app would be handy. We just turn the thermostat down to 15 and it then doesn’t take long for the house to recover. Always a fan heater if necessary.

As for changing the thermostat if the house feels a bit cool can be just as easy to put on a cardigan.

🙂 🙂 Most of our landline calls must be to find a mislaid mobile.

We use a pc not a mobile to set the controls of the Hive.

Paul says:
17 October 2015

As an experienced heating engineer of many years experience I personally don’t feel the need for this level of control, I am naturally more aware of how my heating is performing and use a smart “learning” thermostat centrally located in my home. I regularly adjust thermostatic radiator valves to suit occupancy and otherwise just leave it to do its thing. Over the years the only product that struck me as invaluable is the controlled radiator valves that allow individual control of each room from a central location, as someone has previously said I have to question if the actual savings for the app style (once the novelty has worn off) will justify the purchase and maintenance of the system. And such is the pace of progress these days most will be outdated or superseded very quickly. My biggest advice to anyone is insulation, insulation and more insulation, keep your home as draught proof as possible (if cold air is coming in warm air is going out) and that will prove to be a wiser investment in the long run. I am more or less energy self sufficient with solar panels and a wood burner, the energy payments received for the solar panels more than covers my combined energy costs and the wood burner heats my home in the colder months throughout (4 bed semi with loft conversion) The biggest investment I have made since moving to my house is insulation, even stripping a dormer roof and walls to get access to fit celotex. As I am south facing and with the sun out enough solar gain comes in to keep the heating off all day and well into the night. As an “oldie” I am not that driven to complicate my life more than I have to and stick with the “keep it simple” school of thought (within reason) but horses for courses, if these control systems encourage energy use awareness then its no bad thing. Just not for me, thanks.
Whatever next, WI-FI kettles, oh wait!!!! there are!!

I still see people talking about adjusting their heating on a regular basis in order to achieve the savings and other comments that it makes you energy conscious . No. I’m sorry to say but I think with the best will in the world most people will tire of doing manual adjustments and will forget at times, and from what I’ve seen of energy meters not so many people look at them after a few months. The idea of getting your phone to remind YOU to turn off/down the heating when you are away is funny. The best solution is a zoned system with proper automation. Meaning automatically makes the adjustments by knowing which zones are occupied (and by extension if the house as a whole is occupied) and catering for external conditions – including other subtleties like adjusting water temperature to optimise boiler efficiency for condensing boilers, and may even go as far as accounting for humidity for example.

I agree wholeheartedly that the first line of defence should be insulation, heat exchangers, and making the best of solar gain. If you still need heating beyond that then the second line of defence should be a PROPERLY automated heating system which you rarely need to interact with. Does such a thing exist? Yes, I have one as part of a wider scale home automation system which BTW also automates lighting amongst other things – saving a bit more energy. But saving energy was not the motive it just happens without my thinking about it which I think has to be the best way for real human beings.

If I had to choose between one of the dumb systems based on its energy saving potential then I’d say go for one which gives you zoning. It will probably cost more, so depends on whether your motive is cost saving or planet saving.

Houses that are occupied most of the time don’t need “smart thermostats”.

Hi I’m an heating engineer of a good few years. I personally agree with some of the comments in that if you turn it on you will have to pay for it sooner or later. I just put on a thermal jacket. And insulate then insulate some more. Then comes the control’s. I think open therm should be more available and standardised. For those that don’t know what it is. A magine a pan on the hob at full pelt, you turn it down to a simmer. That is opentherm as I understand it. It controls the boilers burner directly. Also there is no on and off as with a normal room stat so there’s less wear and tear.

I have experience of both the Owl system and the Tado system.
The Owl system can be fitted as a hard wired system with the thermostat directly wired to the boiler or as a wireless system with a relay unit controlling the boiler. I have installed both types in different properties. In my instance the hard wired system was simple to install as it was a straight replacement of an existing thermostat (installed in under 30 mins). The previously installed time clock is simply left in ’24hr on’mode and the system is now controlled by the Owl system. I am very pleased with the performance and I like the ability to monitor the performance of the system through the website and to be able download the data for further analysis. I am not convinced by the system’s claimed ability to adjust the starting time based on the outside temperature and the thermal performance of the property. This rarely reaches the target temperature at the set time – this may be influenced by my boiler being a bit small for my house. This system seems to be reducing my oil consumption – principally from the ease of turning the system off when the house is empty and the ease of heating the house before I get home.
The wireless installation has been installed in a holiday property in the French Alps. It is there principally to give frost protection – I do not understand why the Which report does not acknowledge Owl’s frost protection ability as it works perfectly in this application. The ability to switch the system on and off remotely is a real boon in this application.
I have also installed a Tado system in my daughter’s property. This has proved to be successful although she did have problem with the Geo-tracking system switching the system on whilst she was at work – Tado thought this was due the close proximity (1 mile) of her work to her home. The system also switched the heating on full during the summer when she had a problem with her internet router. This system operates reasonably well and has been improved by a recent update that allows different temperatures at differing times of the day – although the Owl system is far more flexible in this respect. Again, despite Which reporting that it does not give frost protection, it has this facility. The Tado system for anticipating the time to turn the heating on to hit the target temperature seems to work reasonably well in this application.
Overall I would recommend both of these systems. The Owl system has a lot more flexibility but is a bit more ‘hands on’ . The Tado works pretty seamlessly.

Andy says:
26 October 2015

Having got a 7day 6 time thermostat that I can move around the house plus TRVs on all my rads I don’t see the necessity of extra control. Geolocation sounds good but not sure it would cope in a family environment with 4 mobile phones to keep track of and I “worry” the kids would come home to a cold house or that it would keep turning it on before its needed as we move around the local area. So I can see the advantage for e.g. Single people or couples who work irregular hours etc but not so much for a family that’s already got pretty good controls…

I’m uneasy about the way “smart thermostats” are being promoted and discussed. The latest Which? article rather skates over whether they are ‘value for money’, making no comment on the snake-oil salesman style of “could (get-out #1) save you up to (get-out #2) £150…” – an utterly meaningless claim by British Gas. The next page does cite a British Gas report which (I’ll paraphrase) concludes that if you’ve normally used your common sense previously then their Hive will actually cost you more to run than not having it.

And there’s an elephant in the room which is daft to ignore – the cost of installation.
So , a gadget costs say £150 (and that’s on the low side).
It requires “professional installation” – let’s guess at £150 on top.
Oh! And the ‘multi-zonal’ facility – such an alluring buzzword that many will see it as a ‘must-have’. The Honeywell wireless radiator thermostat is available right now online at either £60 or £100 supposedly an rrp of £150! Let’s be generous and say £60 per radiator. My house (an ordinary family home) has 18 radiators, so that’s an extra £1080 for the gizmos plus installation, say £10 per radiator (not forgetting the ongoing need to replace 18 batteries every so often – it’s bad enough remembering to do one smoke alarm never mind 18 scattered all over the house).
So this new toy costs not £150 but £1560 – and the claims for savings being made by the industry are utterly unachievable over the lifetime of the product.

I agree with the contributor who says that most people will quickly tire of this new plaything – if it doesn’t break first. I conclude that these gadgets are a waste of money as replacement devices.

We had the Hive installed for £140 although it was on special offer at the time.

I own the OWL, overall I am happy with it, I am not able to say if it has saved me money due to so many upgrades to the house happening at the same time and trying to compare it with a completely different previous system.
I installed it on a brand new heating system at the start of September 2015, the house previously had electric radiators, I chose it as it has the ability to control heating and hot water and be hardwired and or wireless (I forgot to install a cable for upstairs thermostat) unfortunately the wired stat (which can be used wirelessly with the addition of a receiver) also uses battery’s to power it. There is apparently a cabled powered stat available but this was not made clear by the manufacturers website or the various suppliers so I only discovered it once I received the units and looked on the packaging, so I was unable to ensure that I got exactly what I wanted, I would rather not need to change battery’s. I purchased an additional stat and wireless receiver off of a well-known online auction sites saving myself roughly 40%. For me price was a significant factor and I could not justify the radiator based system for the functionality it gave, owl was my second choice system, my first though could not operate wirelessly and I was unable to identify a simple way of enabling an alternative to a dedicated hardwire link.
If you can follow wiring diagrams then the owl can be installed by a home owner, it is no more complicated than a traditional stat and controller based system. The system was easy to set up and I also purchased the energy meter that uploads info to the web via the same hub.
Each wireless receiver can pair with 4 stats, so you can monitor a larger area of a zone to ensure you get a more even temperature, this gives you a max of 16 stats in a house over 4 zones, and I use simple rad TRVs to prevent overheating. My main downstairs stat is in a room with large thermal gain and large thermal mass (deliberately built so when extending and renovating), this room is the main living area during the day. There is only 1 set of wiring connections on a receiver so it can only be linked to one zone.
For me I like the ability to specify the different status temperatures, like a previous poster stated, it does have a frost protect function for when you are on holiday, it then has a standby temperature which I set a temp which requires you to be active, I then set high temps for times when we are most likely to be less active i.e. evenings. Upstairs I set a higher temp first thing in morning to make getting out of bed easier and a lower temp at night to encourage sleep. The owl is not turning the boiler on and off for set periods of time it is adjusting the temperature for differing times of day and differing statuses so the boiler fires whenever as necessary, this is good as it takes more energy to raise the temperature than it does to maintain it. The system does do some form of weather compensation based on online forecasts and your location.
The owl product is supposed to learn how long it takes your house to warm up and adjust itself appropriately, it the time you set for a temperature is the time you wish the house to be at that temperature.
I have dry lined the house and I am in the process of upgrading roof insulation foil faced pir type to improve efficiency, I have insulated under all the floors and sealed as many drafts as I can, whilst maintaining under floor ventilation. We also have multi-fuelled stoves.
You can adjust the temperature of the system temporarily up at any of the stats.
I would like the ability to do more via the app, this could be provided in the future with an updated app. It would be useful if the energy monitor could work with the Gas system as well although I can see how this is a bit more complicated. I miss not being able to actually see the temperature on each of the stats.
My main issue is signal strength, I have weak signal between base station and the HW controller and the receiver and upstairs sensor. Unfortunately although you get a 4m cable with the temp sensor for HW this can still limit the siting of the controller so in my instance the tank sits between the controller and the base station, moving the base station with router etc. to centre of the house has not improved this, I believe the tank and distance affect the signal strength between the upstairs stat and receiver. Some form of repeater unit would be useful that I can install in a position that does not have the tank between it and the various devices.
I do not really miss the relocation feature but can see how the system could be upgraded to incorporate it, I also can see that the system is modular and therefore expandable, i.e. a module that can be connected to the house alarm that automatically sets the system into away mode if it was set.
An upside of the system is that Owl publishes the API and stats which standards it uses so that 3rd party users can make products that interface with and can control the system, it also means that if Owl ever stopped or changed the service the system could be controlled via a Raspberry pi or similar.
I note how similar one of the devices in one of the other systems which is reviewing.

Jerry says:
2 November 2015

PLEASE DO NOT BUY THE NETATMO FOR SMARTPHONE based on the premise that it is easy to install yourself. The issues are as follows.

1. The back box is not compatible with UK wall boxes (i.e. the screw holes are at the four corners of the Netatmo back box and not in the normal position to screw directly into the wall box that the old Thermostat came out of.

2. The Netatmo compatibility checker stated that it was compatible with my boiler and the Heatmiser Thermostat I was replacing. When I received the Netatmo I found that the wiring diagram only supported volt free switching whereas my boiler is configured for 230V switching.

3. There is no support line available for Netatmo, only an email address so it is not possible to talk to anyone while you are installing (Heatmiser have a technical hotline and when I installed my old Thermostat five years ago they were extremely helpful). I emailed Netatmo over a week ago with a picture of my wiring, the wiring diagram supplied by Heatmiser for my old Thermostat and I am still awaiting a reply from them.

So based on these issues and the abysmally poor level of customer service I would not describe the Netatmo as possible to installed without thorough research first.

On paper the feature for the Netatmo are extremely good, including support for Windows phones, but when buying you really should consider the costs of getting it professionally installed unless you are happy replacing your old wall box yourself and you are confident that your boiler is already set up to support volt free switching.

I am very disappointed.