The most elegant and diverse new fireplaces may burn liquid ethanol or cans of thickened isopropyl alcohol. You have to refill the fuel by hand. The label "ventless" indicates that a fireplace produces little heat, though it looks warm and may even "crackle" like a wood fire. These fireplaces are truly portable only when nothing's burning, even for the tabletop models with flames about the size of a pillar candle.
Though their cabinets and insides tend to look more traditional, electric fireplaces have no flames. Most of them generate about as much heat as conventional space heaters of similar wattage, and burn the same amount of electricity. They may use flickering lights to suggest dancing flames, and some models allow for watching without generating heat. Some electric fires are truly portable and require no attention while operating, in fact offering remote controls.
All of the new fireplaces can be used outdoors as well. You could place a ventless fire encased in glass beside the swimming pool for just the beauty of it. Or set up an electric fire outside for warmth when you've stayed in the water too long.