Thermostat settings that actually save money

The room thermostat: one number, left alone

Most homes settle somewhere between 18 and 21°C. Within that band, comfort is personal; below it, health starts to argue. What matters financially is the increments: each degree lower saves up to about 10% of the heating bill, so drifting from 21 to 20 is a real saving, while 23 as a default is an expensive habit.

The thermostat is a target, not an accelerator. Setting 28 does not heat the room faster; the boiler works at the same pace, cruises past your actual comfort point, and bills you for the overshoot. Pick the number, leave it, and let the timer do the switching.

Timers beat the leave-it-on-low-all-day theory in most housing. Heating empty hours costs more than reheating from a setback in all but the best-insulated homes, so schedule warmth for when someone is there, with a cooler setback (around 15 or 16°C) overnight.

TRVs: heat rooms, not the house

A TRV (thermostatic radiator valve) senses air temperature and throttles its own radiator, which lets every room run its own climate. The numbers map roughly onto temperatures: 3 is about 20°C, and each step either way moves things a few degrees. They are cheap to add where missing, and they earn points toward a better EPC rating too.

That last row is the one everyone gets wrong. The radiator sharing a room with the wall thermostat should run unthrottled, because if a TRV shuts it down early the wall stat never reaches target and keeps the boiler firing for the whole house.

The free win: turn the flow temperature down

Condensing boilers only earn their name when the water returning to them is cool enough to condense the flue gases, roughly below 55°C. Many leave the factory set to flow at 70 or 80°C, hot enough to spend much of their life out of condensing mode. On a combi with radiators, dropping the flow temperature to 60 or 65 keeps the boiler condensing, and the saving is real: around £70 to £100 a year as a guide.

Two caveats. This is combi advice: if your hot water lives in a cylinder, the stored water must stay at 60°C or above, and the cylinder guide explains which dial controls what. And heat pump homes already run low flow temperatures by design, so leave those settings to the installer.

Smart thermostats, assessed calmly

A smart thermostat saves money in exactly one way: by changing behaviour. Schedules that match your actual life, geofencing for erratic households, and enough visibility to nudge the target down a degree. If you already run a tight schedule on a basic timer, the upgrade buys comfort and data rather than savings. If your heating currently runs on guesswork, it can pay for itself.

Controls can only save what the system can deliver. Radiators half-full of air respond sluggishly whatever the dial says, so bleed them each autumn, and take faults to the complete boiler guide. For the whole-house view of savings ranked by payback, the energy bills guide runs the numbers.