We have a woodburning fireplace that is original to the house. We had gas logs and a nice set of doors installed probably 20 years ago but we basically never used it. It sucks all the warm air from the house up the chimney. The hearth is floor level and we prefer something that has a raised hearth. And we did re-work the bookcases and the tile around the fireplace, but we weren't really happy with the way it all looked after the remodel but we just ignored it. We also finally realized that the mortar between the fire bricks is gone in lots of places, so a fire in the chimney is a real risk, so we stopped using it altogether. It was sort of a dead-feeling area in the living room.
Anyway...
Costco has freestanding electric fireplaces and we finally found one that we liked and ordered it. It fits perfectly in front of the fireplace and in between the bookcases that flank it. We either have to cut down or build a custom mantel, as the one that comes with it is too wide to fit the available space. But that's not a big deal.

It doesn't have the mantel on it right now but you can get an idea of how it looks. Because it fills the entire space and sits up higher, it totally changes how the room looks and feels.

It has LED flames and you can even turn on the embers. Bunch of colors and you can adjust the intensity. It's amazing how cozy the space feels.

So here's my question for this thread....the unit also has a space heater. We only plan to use it with the LED "fire" which doesn't draw much current at all. The unit is rated at 1500W. Most portable units have two or three heat settings plus a thermostat to turn off the heater when the room reaches the desired temp, as @steve-miller explained.
This unit only has a thermostat with a temperature setting. Lowest setting is 71 and it goes up from there. There doesn't seem to be a way to select hi/med/lo. I'm kind of assuming that it's always running at 1500W and it only goes on/off based on what the thermostat is set for. Does that seem reasonable? I turned it on briefly to be sure that it does actually work, but turned it off before the thermostat kicked in and did it for me.
Here are the specs for the insert. When I turned it on I could see the quartz elements at the top of the firebox insert, and a fan went on.
https://www.realflame.com/landscape-vividflame-electric-firebox
@steve-miller - BTW, the instructions with fireplace insert simply say you need a 15A circuit. It even says it's preferable to have a dedicated circuit, but not a requirement. That surprised me, as I'm on the same page you are with respect to space heaters.
And of course they say if your breakers pop, well then you need to do something. We have the Ting gizmo, so it might catch a potential problem.
As I said, we don't plan to use it as a space heater, so this is mostly an academic exercise. If I did want to use it for heat, I would get our electrician in and have the circuit that this thing is on separated out and create a new 20A circuit so it could be used without having to be concerned about it.