The size of an electric boiler is measured in kilowatts rather than physical size. The higher the KW the more powerful the boiler. As a rough rule in addition to providing hot water (if needed) each radiator requires 1.5KW to heat, therefore if there are 8 radiators then a 12kW electric boiler will provide sufficient central heating.
• 4 Radiators – 6KW
• 6 Radiators – 9KW
• 8 Radiators – 12KW
• 10 Radiators – 15KW
Before purchasing seek professional advice from a qualified installer.