[Khledar]

By vertical do you mean the surface area that is exposed is perpendicular to the ground (the air flows horizontally) or that the exposed surface area is parallel to the ground (air flows through vertically). Slightly confused but I believe most people run their radiators "standing up" or perpendicular to the gound. If you're running the radiator so that its surface is parallel to the ground the only thign to watch out for is that since heat rises pushing the air down through the radiator might be slightly less efficient than pushing the air up through the radiator. Other than that *slight* issue, i think both ways are equally do-able.