Help with flow rate and picking out a new pump.

[mikemurph6]

I have a old hayward 1HP super pump which was running fine last year but its about 20 years old. I just purchased and I am in the middle of installing a new pool heater, Raypak 336k BTU NG to replace the 25 year old and broken 185k BTU NG heater.

My pool is 25k gallon inground pool. I have calculated my total length of pipe to be about 130 feet, 1.5" flexible pvc pipe. Pump is 2 feet higher than level of the pool. I have a DE filter. There are 5 90-degree elbows that I know of and one 3-way diverter.

My question is do you think I need a higher powered pump? Based on all my calculations I need a 2.5HP Hayward super pump...is this correct?

The whole system confuses me, we just moved in last year and the pool ran great and stayed clean and balanced with help from this forum but based on the pump size and heater size it seems like the whole pool was incorrectly setup and undersized.

 

[JamesW]

You don't need a bigger pump. A 1 hp total should be plenty.

A two speed or variable speed pump is recommended for most people.

 

[mikemurph6]

You don't need a bigger pump. A 1 hp total should be plenty.

A two speed or variable speed pump is recommended for most people.

Great, thank you. How did you determine that?

 

[JamesW]

You really don't need more than about 40 gpm, at most.

Trying to get a lot more flow by increasing the pump size would mostly just waste energy and over pressurize the system.

 

[mikemurph6]

With 40 gpm and a 25,000 gallon pool I would need to have my pump on for 10 hours a day then right?

Also how did you calculate that my rate would be 40gpm with the 1HP pump. I tried figuring out my total head but I don’t think I did it correctly.

 

[ajw22]

Please read Determine Pump Run Time - Trouble Free Pool

Pool turnover is a myth and 1 HP is plenty unless you have exceptional water features. Head calculations are not needed in most simple pools.

 

[mikemurph6]

Please read Determine Pump Run Time - Trouble Free Pool

Thank you, very helpful article. I appreciate it.

 

[JamesW]

Head loss through a system is not a single number. It varies depending on the flow rate.

The faster you want to push water through the system, the more pressure (head loss) it takes.

The pressure increase is exponential as is the power usage.

Here is the head loss through 100 feet of 1.5" pvc pipe:

Gpm.......ft/sec..........head loss in feet
20.............3.2...................2.6
30.............4.9...................5.5
40.............6.5...................9.4
50.............8.1.................14.3
60.............9.7.................20.0

So, if your system was equivalent to 100 feet of 1.5" pvc pipe, you could graph the above numbers for gpm and feet of head on a graph to display the "System curve ".

You would then graph the published pump curve on the same graph as the system curve to see where the pump curve crosses the system curve.

That point is called the operating point.

Typically, you should limit suction to a velocity of about 6 feet per second and return to about 8 feet per second.

If your suction is a single 1.5" pvc pipe, you would want to try to stay below about 40 gpm for best efficiency.

The heater will be relevant to the flow rate as most require about 35 to 40 gpm minimum.