No, he meant what he said. If all spaceheaters dumped 1 BTU into the room for every .0002928 kWh they sucked out of the wall, they'd all cost the same to run per BTU. So, cost comparison would be stupidly simple: Buy the cheapest one in the size you need.
Kind of like 100% efficient. We all know full-well it's impossible, but you can calculate things to say anything you want if you ignore context and hence, what the numbers really mean.
Not true, some things make you feel warmer than others, for example the radiant dish style heaters that heat only you and not the air. A heater with a fan will not warm you the same as a radiant heater, it will heat the room more even though.
Anyway back to the original posters delima.
Make sure the fins on the baseboards are clean and the units themselves are in good shape. Make sure the electric wiring is in good shape, so that you aren't sending electricity into a ground somewhere
Just like a radiator they can be sending heat out the wall, so some sort of radiant barrier between them and the wall can help reflect heat into the room and not through the wall. I really like the silver foil bubblewrap like radiant insulation sold at Lowes.
Reflectix Inc. | Do-It-Yourself | DIY Behind Hot Water Radiator
Above all seal air leaks, insulate everywhere you can, get some heavy curtians to close at night.
I'd also recommend a small kerosene heater for those really cold days and to have around for emergency heat.
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