Thanks for the comments.
The 100mm celotex insulation was installed last week so no option to change now.
Heat load with a internal temp of 22C and external of 0C is less than 1.8 Kw/hr
I have also found this unit which has an inverter drive and a remote controller Ebay 295373873999
Would seem that controller would offer better control of living area temperature as it has a timer function.
Im sizing the radiators on a water temperature of 45C.