This document describes a proposed technology for highly efficient water heating using magnetron effects. It begins by providing background on previous work exploring this approach. It then describes the operating principle of a magnetron, how electrons move and interact with electromagnetic waves in the presence of electric and magnetic fields. Experimental results are presented showing increased heating efficiency in a "sub-critical mode" providing confirmation the approach is viable. Finally, it outlines proposals for further developing the technology, including patenting, designing prototypes from 1-100kW, and eventually industrial-scale heaters of 100kW or more.