Ours is just 17.5 all the time. If it feels a bit chilly its A jumper and/or burn something.
TBH heating has been used more to keep damp away as opposed to cold in recent months.
We had a few frosts in December, it was actually icy a few mornings in places, but it didn't last and didn't cut deep as the ground temp is so high, and wet.
Feb/March seems to be the new winter, if at all. Goodwood members meeting is a good gauge of when it'll snow.
Days are getting longer...