overflow question

[scottallert]

I have a supreme mag 9.5 pump that is going in my sump that pumps 950 gpb
but the guy at the lfs said it will only pump 740 gph due to the fact it has to pump vertically,
im making an overflow box(not really a box, more like pvc pipes)
ok the question should i go with 1.5'' pipe or 2'' or something else?

 

[natclanwy]

He is right your flow rate will decrease significantly based on the amount of verticle pipe you have and slightly for any horizontal lengths and extra fittings. Also the diameter of the return pipe will effect the flow rate significantly.
I think 1.25 pipe would be enough to handle the drain but I'm not familiar with the flow rates on these types of overflows. Normally for a HOB overflow a 1" pipe will drain 600gph, 1.25":900gph, 1.5:1500gph.