I was simplifying the calcs. 85% efficient is the boiler efficiency. I went with 50% line losses to account for all other losses. .5 times .85 is .425. I think you will find that my final answer is around the correct number even though I didn’t do it the right way. I didn’t expect there would be anyone on this thread that would be bothered by my shortcuts. Next time I will show every little loss in every device between the coal fire and the extension cord. sheesh.
A boiler isn’t a power plant.
Looks a lot more like just making stuff up to me.