Wow, I read 17 and 18 degrees Celsius!
During Winter that is too cold. The thermostat is on 20.5. It switches on at 07:00 and off at 11:00. Then on again at 17:00 and during weekdays off at 23:00. I shut the heating all toghether late March, early April. Not needed anymore. I also wondered about the difference between 18 degrees in Summer and the same 18 degrees in Winter, which feels a lot colder
Humidity levels perhaps?