Richard wrote:

Does anyone have a rough idea of how many kw a large storage heater is
set on number 5.

The biggest normal domestic storage heater is 3.4 kW (giving 24 kWh
'charge' in 7 hours).

The 'setting' (input charge control) is just an on-off thermostat, and
doesn't affect the power consumption, except in the sense that the
latter will be either zero or 3.4 kW.

--
Andy