On Jan 20, 12:06*am, wrote:
Right, the equivalent of putting the radiators on outside walls.

Then the remaining question is- do I blow it back AT the wall (the register is on the ceiling, against the wall) or sideways along the wall?

It's not the equivalent. Radiators or registers are put along
outside walls because those AREAS, near outside walls, need
the most heat. The intent however is not to heat the wall
itself, rather the air near the wall. With a radiator you don't
have choice in where the air is directed. With a register, you
do. And heating the wall above room temperature just means
you're going to lose more heat out that wall. I've seen a lot
of registers and I've never seen one where the air was
directed at a wall and not into the room.