The problem I had with space heaters is many didn’t last more than a winter. You can’t repair them. I’ve tried a bunch of different varieties and I think they are designed to fail after a few months.
Don't listen to this nonsense. The most efficient heater is the one that heats up room the fastest or retains heat the longest! They’re all basically cost the same per hour if they have the same wattage. So you save money by not needing it on as much as possible. Best bet is a smart heater that is set to turn on till you hit the right temp and then turns on when it goes below a set temp. Better still if it has some kind of thermal mass to hold onto heat.
The laws of nature state that you can not create or destroy energy. You can only convert it from one form to another form. Every single watt used converts to the same amount of heat. One heater can not magically do that any different than another.
