In article m, John
writes

But is that what it does when it's heating? Does it chuck cold air out of
where it would put out warm air when it's cooling (IYSWIM)?

Exactly right, hence the term "Heat Pump".
The down side is that they generally don't work at low outside
temperatures.

John

No they don't!. The one we have is fine except when it gets down to say
less than 2-3 deg c when it spends a lot of time defrosting itself which
means that its taking quite a bit off the mains in order to so that, but
anything above those temps, its fine.

If you could imagine its working in reverse to what its doing in the
summer months.. its trying to "cool" the outside air and get rid of the
heat inside the room!...
--
Tony Sayer