Does anyone know if I can use the figures in this thread to size my DIY overflow box? I assume the horizontal flow numbers are the most applicable, since it won't have the height to achieve the vertical flow numbers.
I did some quick calculations and it looks like the flow rate is fairly consistent - around 7.96 gallons per minute per square inch of cross-sectional area. I'm using a Quiet One 5000 at around 5 feet of head, which should output about 900GPH. I'm not sure how much extra flow I should allow for. Would 25% be enough? That would require an overflow box capable of 1125GPH or 18.75GPM.
If everything else is right, that would mean I would only need 2.36 square inches of cross-sectional area in my overflow box. That doesn't sound like much. Is there any detriment to building the oveflow box far larger than it needs to be?
This guy suggests that the outer section of the overflow box should be lower than the inner section but he doesn't provide any solid reasons for it. Almost all the overflow boxes I've seen have the inner and outer sections at an equal height. As far as I can tell, the flow would be the same in the uneven configuration (if not lower). Am I missing something?