Ask a professional engineer about the energy used by the heating systems they design. Their response is almost guaranteed to apply to the “fuel” energy (e.g., natural, gas, propane, oil, pellets, etc.) used by the system’s heat source(s).
With the exception of systems using electric boilers or heat pumps as their primary heat source, few heating pros give much thought to the electrical energy used in their hydronic systems. Perhaps they view such energy as trivial in comparison to fuel energy. They might regard it as a “parasitic” necessity for delivering heat produced by the high-efficiency heat sources they specify.