Great idea, however the feasibility of a 5.5KW supply is at least doubtful in most places.
I have a similar setup using a 3phase heater, so heat settings can be changed as needed by turning individual (3) elements on and off. Say 2, 4 and 6KW.
The heater can be directly attached to a 1.5" NTP adapter and has a screw in type option for the electrical contact cover.
http://www.ebay.co.uk/itm/2719475258...%3AMEBIDX%3AIT