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, robust |
| 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.
