Maximum Flow Rates for PVC, Schedule 40 Pipe
Pipe Size in Inches	Suction (GPM)	Return (GPM)
1	22	27
1 1/4	37	47
1 1/2	51	64
2	84	105
2 1/2	119	149
3	184	230
4	318	397
5	499	624
6	720	901
8	1248	1559
10	1966	2458
12	2791	3489

Maximum Flow Rates for Copper Pipe, Type K
Pipe Size in Inches	Suction (GPM)	Return (GPM)
1	19	19
1 1/4	30	30
1 1/2	43	43
2	75	75
2 1/2	116	116
3	166	166
4	291	291
5	452	452
6	646	646
8	1126	1126
10	1749	1749
12	2507	2507

This chart illustrates the pump's size and their GPM ability:

Maximum Flow Rates for Copper Pipe, Type K
Pump Size (hp)	GPM	PVC Pipe Minimum Pipe Size Suction - In Inches	PVC Pipe Minimum Pipe Size Return - In Inches	Copper Minimum Pipe Size - In Inches Suction / Return
1/2	70	2	1 1/2	2
3/4	80	2 1/2	2	2 1/2
1	85	2 1/2	2	2 1/2
1 1/2	100	2 1/2	2	2 1/2
2	110	2 1/2	2 1/2	2 1/2
2 1/2	120	3	2 1/2	3

If the pump is oversized for the plumbing system, you will pump less water than a smaller hp pump because the larger pump builds up too much friction and actually slows down the water flow. An example is a ¾ hp pump with 2" suction and 2" return will pump more water than a 2 hp pump with the same pluming because the plumbing is sized too small for that pump.

What we've found happens is a pool service or maintenance person will sell the owner a bigger pump, touting it as a "better deal". But it's actually a dis-service as the pump has to work harder, longer, wears out faster, uses more electricity and pumps less water. This only costs the owner more in the long run.

Does your house cleaner know how to stucco your walls? Does your house cleaner know the correct primer to use under the final coat of paint?