Originally Posted by Roger Chapman

asalcedo wrote:
I am going to place a new radiator in a new room in the house.

Because of access constraints, the flow and return valves will be
located on the same side of the radiator, one above the other.

I am going to place the flow at the bottom and the return at the top,
is that correct?

No, you want the return at the bottom where the cooler water ends up.

Putting the return at the top just gives an easy return path for hot
water that hasn't been given much chance to give off any heat. Most of
the radiator would remain cool as the incoming hot water rises close to
the side of the radiator and exits out of the top.