Ideally, you would have a suitable feed direct from main fuse board. This wouldn't be an expensive or big job for an electrician to do.
I run mine from a 13a socket on a timer via a heavy duty extension cable. NOTE- the extension cable must be FULLY unwound, not coiled up etc. Timer has a max load of 3120W. This is my 3rd winter with it & it's been a life saver.
Next year though, I'm going to get a dedicated line from the fuse box to one socket.