The absolute most important thing you need to understand with heat pumps is that they are at their most efficient when the flow temperature through either the uf loops or radiators is the lowest possible. Many heat pumps are left at factory settings and are not optimised and while you may well have a nice warm house you will pay a fortune on your esb bills. And the only real way to optimise is by trial and error by reducing the flow temperarure every couple days until you feel cold, then you've gone too far and set it back to the last setting where you were comfortable.
You need to do this for at least two outdoor temperatures, one mild and one cold.
Also remember it is a false economy to shut down rooms which you're not using, keep all room heated and allow the hp do what it does.