ID1

Thanks - that is an interesting option. According to the specs it's a bit bigger than the inside unit of a small split system and a bit noisier. But it does avoid the ugly box outside & it's a simpler installation so definitely worth thinking about. That is the sort of running cost I was hoping might be achievable.

I have been retired for a while but have always been frugal. I have traditional gas central heating in my 1990s 3 bed detached house with cavity wall insulation. The heating only comes on for 4 hours in the evening (apart from periods of sustained sub zero temperatures but we have not had a winter like that for some years). When at home I spend most of the day based in my small study (3m x 3m) and dress up warmly. It's not just about economy, it's also an incentive to keep active and not spend the day on the sofa. As I am getting older I am becoming less tolerant of colder temperatures and so last winter, when the study temperature fell to about 12C, I resorted to a small fan heater (1kw - on about 50% of the time). There are also an increasing number of days in the summer when the heat is uncomfortable. As I get older I think I will increasingly want heating & cooling. I am usually quite comfortable between 17.5 & 24C and this would probably be my target for the study. My study has a suitable outside wall for an air to air heat pump. However, given the small size of the room, is it unrealistic to think that a mini split air pump could be efficient?