We have three heat pumps in our house. Two were installed some years ago high up on the wall in adjoining rooms, with the heat pumps virtually back to back, and running off the same outside system. It hasn't been the most successful approach, and the person who came to put in the third pump a couple of years ago pooh-poohed the way things had been done. By which time it was a bit late, of course!
The result of having both the pumps running off the same system, and of both of them being a bit underpar for the work they're supposed to do, is that in the room we use as our main sitting room, it can be warm up around your head, but cold around your feet. It always seems a bit ironic to be paying for a heat pump to function when we have our legs encased in blankets. Still keeping warm is the prime thing, especially as the winter draws on.
I was talking to one of my colleagues at work yesterday and she was saying that they have a heat pump up on the wall in their house too - it's common practice, of course. On the weekend they were experiencing the same problem as we have: hot heads, cold feet. Her husband went and got the dehumidifier, plugged it in, set it going, and voila! it drew in the cold air and allowed the hot air to move around the room.
Result: warm feet. Now, do we want to go out and buy a humidifier? And is the extra drain on the power bill going to be worth it?
The third heat pump that I mentioned above is installed in the hall, which, because of the nature of our house, is the coldest area in winter. When that heat pump is going, however, not only the hall but the adjoining rooms warm up. It's down near the floor, for one thing, and it's a bigger model for another. I guess in a way it acts in a similar fashion to the dehumidifier: it pushes the cold air around and pulls the warm air down (well, I'm sure that's not technically what happens, but it's something along the lines of what happens).
I'm thinking about these things more at the moment, because we've run into a cold patch, and as well, in three days I retire, and won't get the benefit of my workplace's heating during the day...!