an ethanol fire is an ornament, not a heater, because it makes quite a lot of water vapour, which you have to ventilate out, or it will cause condensation and damp. Having the window open probably means the room will be colder than if you didn't have it.
Somebody better at chemistry can work out how much water it makes per litre of fuel.
I don’t have experience but I did look into bio ethanol fires, from memory they were incredibly expensive to run - like £50 a time or something as the fuel costs so much - so you’d only do it occasionally. Things may have changed since but worth checking.