"Kuldefall" : where to place my electrical heater

When I moved in here, two and a half months ago, this electrical heater was standing in the corner, just like now.
It should be mounted on the wall, but I was trying to decide exactly where.
In the meantime I bought two freestanding radiators, keeping my apartment and me warm.

So where should I put the heater on the photo?
I thought I should keep it away from the windows because of the curtains.
In my imagination curtain and heater means fire.
I was seriously contemplating using one of the "free" inner walls, with no curtains.

Now one of the locals told me, the heater should go under one of the windows.
He explained that cold air "falls" from the window down to the floor,
and the heater prevents that from happening.
He said the curtains will not catch fire.

So now I have switched on another heater under my kitchen window (below).
Originally I thought I would have to shorten the curtains first.