Only if you want them to do any good.
All heating vents need to go under or at least as close as possible to all windows and door opening.
You have cold air coming in and falling, the heater preheats that air and convects warm air up into the room.
Why would you not want it under the window? Will it not fit for some reason?
Then can go any place but as stated are best under a window.
They also make ones that are more square and have built in fans.