Advanced options
The honest caveat: a smart thermostat saves by heating LESS when you're out or asleep: if you already run tight schedules and turn things down, it has little left to find. The free alternative captures most of it: each 1C off the thermostat cuts heating ~10% (worth ~GBP 90 on a GBP 900 bill). Smart TRVs on individual radiators add room-by-room control at GBP 30-70 per valve.
What The Smart Thermostat Savings Calculator Works Out
- Saving per year: your annual heating bill multiplied by a realistic saving percentage. Manufacturers' headlines and independent trials converge on high single digits for the typical household: about 9% of a GBP 900 bill, an GBP 80 year.
- Payback: the installed cost divided by the yearly saving. A GBP 200-odd device pays back in two to three winters for the average home, faster for the chaotic, slower for the already disciplined.
- Where the saving comes from: schedules that finally match the household's real week, geofencing and occupancy sensing that notice the empty house the old programmer heated faithfully, weather compensation trimming the morning pre-heat, and the app friction that makes "just whack it up" slightly less automatic. The device saves behaviour, not physics.
- Custom saving percentage (advanced): set your own figure. Homes whose heating runs on schedules set once in 2011 find double-digit savings immediately; a household that already runs tight timings has left the algorithm little to harvest.
- Smart radiator valves (advanced): the number and price of smart TRVs (GBP 30 to GBP 70 each) that turn the spare room and bedrooms into zones on their own schedules, plus the extra percentage they save. The largest wins live in the biggest, least-used rooms.
- Subscription or app fees (advanced): any yearly charge for premium features or cloud services, netted off the saving.
- Saving per month (advanced): the yearly saving divided by 12, though in practice it lands almost entirely in the heating months.
- Net saving over the years you keep it (advanced): the combined yearly saving after fees, multiplied by the years, minus the cost of the thermostat and valves. Compatibility matters at the boiler end: OpenTherm modulation versus simple on-off switching decides how much finesse the thermostat can apply, and heat pumps mostly prefer steady running to clever setbacks.
- Free alternative (advanced): each 1C off the main thermostat cuts heating by around 10%, a free intervention that often outperforms the gadget it accompanies. Decent insulation and draught-proofing outrank any control system in the retrofit order.
Context: Energy Saving Trust on heating controls.