And the 10 kW is the same as the 12 kW I believe. So if your installer has done a good heat loss, in theory you have some "headroom".

BUT there plenty of well informed people who prefer the 10kW version. It’s quieter because its two fans run slower.

Defrost cycles need extra power so the 10kW is best for that too.

@realevil Fwiw I have the 7kW model with which I'm, very happy.  There is a 'warts and all' review on this forum, written by me. 

It's not perfect, but I don't know of a perfect machine at the current tine.  However it's pretty good on all major measures and has a good control system, much better than many competitors, as well as performing well.  If I were buying again, I would buy another Vaillant.

BUT there plenty of well informed people who prefer the 10kW version. It’s quieter because its two fans run slower.

Defrost cycles need extra power so the 10kW is best for that too.

Any thoughts on this (larger) heat pump? Was main recommendation from a local heat Geek and certainly seems like a solid unit. The 7kw model is too small for the heat loss.

I guess my main thoughts are around noise for this twin fan unit and also if the 2 fans help or hinder defrost cycles?

It will be outside a kitchen window so noise a worry though no bedroom has a window facing it.

Thanks!!