Sauna Heater Electrical Supply Calculator: Plug, Fuse and Cable Size

Before you buy a sauna heater, the question that trips people up is not the price, it is the wiring. A small heater plugs into a normal socket; most bigger ones do not. This calculator takes your heater's kW rating and supply voltage and tells you the current it draws in amps, whether it will run off a standard 13A plug or needs its own hardwired circuit, and the fuse and cable size an electrician is likely to fit. Anything over a 13A plug must be wired by a qualified electrician, and in the UK this is notifiable work under Part P of the Building Regulations.

The current in amps is simply the power divided by the voltage. A 13A plug on a standard ring main can carry up to about 3kW continuously, which is why so many plug-in saunas stop at 3kW. Above that you need a dedicated radial circuit run from the consumer unit, sized so the cable and protective device can carry the load safely. The cable sizes below are typical for a short run in a domestic setting; the actual size depends on the run length, the installation method and any derating, which is exactly what your electrician will assess.