Zoeller Pump Co. information reccomends figuring GPM as follows: basement sq ft divided by 100. take the result and multiply by 1.25 (for clay soils)…so 768/100=7.68. 7.68 times 1.25 = 9.6 or approx. 10 GPM. Does this sound correct? Next I’ve looked at sump pumps and they list 1000GPM at 0 head…down to say 300GPM at 15′ head.
I think your 1000 GPM might be 1000 GPH, which =’s 16.6 GPM the 300 GPM should be 300 GPH =’s 5 GPM. The pumping rate in GPH, which gives big numbers, is a marketing thing. The Zoeller model 53 does 43 GPM at 5 ft and 19 GPM at 15 ft. The Zoeller estimating tool you made reference to is just that it is an estimating tool and what you get in your basement may be a lot more or less than than that what you estimate.