Set your thermostat to 17-21°C
Have done this
Category: Home Efficiency
By programming your thermostat to reach a high of 21°C during the day and 17°C while you're away from home or sleeping, you could save about 2% on your heating energy consumption every month. It's that simple.
All you need (and probably already have) is a programmable setback thermostat. Program it so that your temperature reductions start before you go to bed and end before your alarm goes off in the morning.
Our Home Energy Retrofit Accelerator (HERA) may have a rebate for smart thermostats.