BBN2 wrote:

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It's -2C outside your caravan - would you buy a 400W fan heater to keep you warm?

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I am far from recommending one of the Kings units but suggest your example is not quite right. 

The power draw of an air conditioner is very different from the output. The promotioinal specs show 600 watts power draw, while further down it says 600-900 watts. Which is it? However the specs say 5100btu output, which is about 1500 watts. If heating, that would be reasonable for a caravan fan heater. 

My van has an Ibis rooftop air conditioner rated at 3.2kw output, and it does a good job. An air conditioner with less than half that capacity, as with the Kings would help, but probably only drop the temperature a little. The losses due to the ducting would be part of the reason, coupled with the difficulty of exhausting the hot air outside.

Parked in the shade, or at night maybe it would be OK but in my opinion not much good otherwise. I did not see any specs on noise levels, which is pretty important in a small space.

Also, with air conditioners, the hotter it is the less well they work. This one has a pretty low efficiency (600 watts to produce 1500 watts) which is on the low performance side. Maybe on a baking hot day it would still try to produce that 1500 watts of cooling, and that is when it ramps up to 900 watts. Note the quoted startup power of 1200-1800 watts if intending to run from an inverter. But you would need some pretty substantial battery capacity.