I was going to put a return to the diplay tank from a sump. When choosing a pump do I also have to include the height of display tank in calculating the pump size? The return line will be going over the top edge of the display tank.
The vertical height you feed to the calculator should be measured as the difference in height between the water level in the return section of your sump and the water level in your display. As an example, the water level in my display is 57.5" above the floor and the water level in the lowest chamber of my sump is 8" above the floor. Thus, the static head my pump works against is 49.5" or 4' 1.5".
I can't quite tell from Scuba_Dave's post, but it looks like he is including the height of the return piping. When calculating static head, do not include the height of your plumbing if it goes over the back wall of the tank. The only thing that matters is the height differential between the two bodies of water. Your return pipe could go through the roof and then back down and the static head would not change. All the extra pipe would increase the dynamic head but that is a different animal all together.