DarthKermit: A friend of mine has a heat pump in his lounge and a duct to suck the warm air from the lounge and into the hallway and one bedroom.
He said that it's very inefficient at transferring the heat from one place to the other.
From what I have read this isn't the best solution as the heat from the heat pump isn't hot enough to make it worthwhile. vs say a fire that will be something like 20+kw i.e. 50 degrees+ vs high 20s. (not an expert opinion just how I undestood it)