Please use the calculator to give you a rough idea of the nominal heat output in kW needed to obtain a room temperature of 210C, when the outside temperature is 00C.
For example a room with width 4m x length 5m x height 3m = 60m3 volume
For a new build house with very good insulation divide the volume by 25 e.g. 60/25= 2.4 kW
For a house with average to good insulation divide the volume by 15 e.g. 60/15= 4 kW (the value given by the calculator).
For a house with poor insulation divide the volume by 10 e.g. 60/10= 6 kW
If you have two rooms with an arch in between, normally it is advised to treat as one room, but the arch will stop the heat from travelling – it will convect across the ceiling, and quite a high proportion will be stopped by the top of the arch.
For open staircases, add 10-20%.