Smart thermostats promise to cut your heating bill. Some do. Many save less than the marketing claims, and a few save almost nothing in homes that were already well-controlled. The honest answer depends on your starting point, and what you replace the thermostat with matters more than the brand.
What the real savings look like
The Energy Saving Trust’s headline figure for smart thermostat savings is 2 to 9%. Where in that range you land depends on what you replaced:
| Starting point | Likely saving with smart thermostat |
|---|---|
| No thermostat, heating on a fixed schedule | 7-9% |
| Old mechanical thermostat, no schedule | 6-8% |
| Programmable digital thermostat, basic schedule | 3-5% |
| Programmable thermostat with TRVs and good schedule | 1-3% |
If you have a well-set programmable thermostat with thermostatic radiator valves already, a smart thermostat saves you almost nothing, what it gives you is convenience, not bills.
Brand comparison
| Brand | Typical fitted cost | Subscription needed? | Strengths |
|---|---|---|---|
| Hive Active Heating | £199 | No | Simple app, British Gas integration, solid |
| Google Nest Learning | £249 | No | Learns your patterns automatically, beautiful design |
| Tado V3+ | £169-£249 | Optional £24.99/yr | Best geofencing, room-by-room zoning, weather adaptation |
| Drayton Wiser | £139 | No | Cheapest mainstream option, multi-zone capable |
| Honeywell evohome | £399+ | No | Best for multi-zone properties, expensive |
Which? testing across these brands shows energy performance within 1 to 2% of each other in standardised tests. The difference is interface, ecosystem fit and zoning capability.
When a smart thermostat is genuinely worth it
- Irregular schedules. If you work from home some days and the office others, geofencing pays for itself quickly.
- Multi-zone properties. Drayton Wiser, Tado and Honeywell evohome allow per-room control. A four-bedroom home where bedrooms only need heat for a few hours a day saves meaningfully.
- Heat pump homes. Heat pumps work best with weather compensation, adjusting flow temperature based on outside conditions. A thermostat that supports this (Hive Heat Pump, Tado with the heat pump adapter, native heat pump controls) avoids 10 to 20% efficiency loss versus a basic on-off thermostat.
- Older homes with poor insulation. The longer your heating runs, the more value precise control delivers.
When it is mostly hype
- Small flats with electric heating. Most electric heaters have built-in thermostats; a centralised smart thermostat does little.
- Homes with already-disciplined heating habits. If your gas bill is under £500 a year, the saving will not pay for the device.
- Rented homes where you do not control the heating system. Many landlords’ boilers do not pair well with modern thermostats.
Installation and compatibility
Most modern combi boilers (post-2010) work with mainstream smart thermostats. The thermostat replaces your existing wall control and either wires into the boiler directly or connects via a wireless receiver near the boiler.
Installation costs:
- Self-install: £0 if you are comfortable replacing a thermostat (most modern thermostats include a “no extra wiring” option). The unit cost only.
- Installer fitted: £80 to £150 on top of the device cost.
- Boiler integration with OpenTherm: Add £40 to £80, but worth it for modulating boilers, gives 5 to 10% extra saving on top of headline figures.
Zoning matters more than the thermostat
If you want real heating savings, zoned control beats any thermostat upgrade. A four-bedroom home where the kids’ bedrooms are only heated 7-9am and 6-8pm saves more energy than any single-zone smart thermostat. The cost-effective route is smart TRVs (thermostatic radiator valves) on a few rooms paired with a basic smart thermostat, total cost around £300 to £450 versus £800+ for a fully zoned system.
Sources
- Heating controls and thermostats, Energy Saving Trust
- Best smart thermostats, Which?
- Programmable thermostats, US Department of Energy
Frequently Asked Questions
For homes with no existing thermostat or only a basic mechanical one, yes, Energy Saving Trust data shows 7 to 9% bill reduction. For homes already using a well-set programmable thermostat, the saving is much smaller (1 to 3%).
The native control supplied with the heat pump is usually the best option, it understands weather compensation properly. If you want a third-party app on top, Tado supports heat pump integration.
Hive, Nest and Tado all include a hub or receiver as standard, which plugs into your router. There is no separate purchase. Drayton Wiser uses a Heat Hub that comes in the basic kit.
For multi-bedroom homes with variable occupancy, yes, smart TRVs deliver zone-by-zone control that delivers more saving than the thermostat itself. Cost £50 to £80 per radiator; payback usually three to five years.
