Whitewavemark2 For over 55 years, and in 5 different houses have ever only had our CH on from 6.00am - 9am in the morning and 4.00pm - 10.00pm in the afternoon, most of that time in houses built befor 1900, including the last nearly 30 years in a 550 year Listed Building, which means loft insulation but limited double glazing or wall insulation. Yes, we too have thick lined curtains that are drawn as soon as the heating comes on, or lights are turned on
Our thermostat, is, and has always been set at 18.5 degrees. We do not fiddle with the thermostat, although in bitterly cold weather - like now, we will sometimes put the heating back on after lunch. We find the temperature in our house as comfortable as ever.
Whatever the recommendations, I find houses with temperatures set for 20 degrees or more, stifling hot. Despite its age our house holds the heat and the internal temperature does not fall dramatically during the day.
DH generally wanders round the house in a T shirt, and always has, I feel the cold so will usually have a sweater over a thermal vest - and always have.
I have in the past suffered from hypothermia, I know it and recognise it, but never in the house.