That's an interesting idea, 2 units one at the top of the house for cooling, one at the bottom for heating,...........hmmmI think that the warm air from downstairs flows up the top of the stairwell to the bedroom with the cool air flowing underneath it, a bit like a thermosyphon. The effectiveness of this is such that I've not yet seen the need to fit another unit in our living room, although I am still thinking about it.
Desp