bobscott wrote:...Aircon which can be made to heat as well as cool is an option that has been discussed on this forum before. I always thought it an expensive way to heat rooms, but one or two people say that's not true...
It depends what you are comparing it with and also what type of aircon.
As Martin pointed out a good quality aircon unit could put 3.5 kW of heat into a room but only consume 1 kW of electricity to do so. A normal electric heater, e.g. oil filled radiator, radiant fire, fan heater would put 1 kW of heat into the room for the same consumed energy. Thus an aircon unit is much much cheaper to run. Compared to a wood burner or oil fired central heating it is probably more expensive. I would guess a central heating system running on olive waste is probably the cheapest to run.
Not all aircon units are as efficient as the figures Martin quoted. I had some ordinary ones installed when I first built my house because they were cheap and I wasn't sure how much I would use them. They are nowhere near as efficient as a good quality inverter type and hence more expensive to run, although still cheaper than other electric heaters. I found I rarely used the bedroom ones but quite often used the living room one on the hotter days in summer, i.e. if internal temperature gets over 30 C, so I changed the living room one to a higher powered, high efficiency inverter type. I've never used them for heating.