Calculating optimal pump size for my system?

[Phillbo]

What do I need in order to calculate the best size pump to buy for my system ?

Current pump is a 1.5hp.
Filter is DE - size ?
PVC Size ?
21K gallon in ground pool.

Do I need anything other than the filter / PVC sizes ?

I'll be converting to salt, i'm sure that needs to be factored in as well.

[duraleigh]

Hi, Phil,

Filter size is probably the single most important element. You should be able to find a gpm rating for that filter on the man. web site. Take that rating, say it's 70 gpm, and look for a pump with a curve that will push about 50-60gpm through the filter. In other words, size your pump so it's somewhat smaller than the filter's capacity.

Find the pump curve, again, on the man. web site. To interpret the pump curve, you'll need to know tdh (head). For most pools that don't have anything extraordinary, 50 seems pretty close for head.

To my knowledge, salt has nothing to do with your pump size.

[Phillbo]

Alright .. the filter is a Purex Triton Nautilus FNS 48. The flow rate on the sticker says 144 (3gpm/FT2) whatever that means but I found a site with some specs that quote a 96 GPM flow...

current pump is a 1.5, can I get away with a more modern small pump ? Any suggestions ? I'm looking for both quiet and efficiency ;)

[mas985]

Do you have a spa, water features or a vacuum style cleaner that requires high HP?

If not, you could probably go down to a 3/4 HP full rated high efficiency pump. If you do, then you might consider a two speed pump (1 HP full rated or 1.5 HP uprated).

[Phillbo]

no spa but I do have a Hayward Pool Vac like this .. http://www.intheswim.com/Automatic-Pool-Cleaners/Hayward-Automatic-Pool-Cleaners/Pool-Vac-Ultra-Automatic-Pool-Cleanerby-Hayward-/

[mas985]

3/4 HP may be enough if you have a dedicated vacuum line and valves to isolate it into the pump. I cannot say for sure. However, you may want to stick with a 1 HP full rated two speed. In the end, you may save more energy with the 2 speed anyway since you can run it on low most of the time and on high only when vacuuming.

Too learn more about pump sizing, check here:

http://poolplaza.com/pool-pump-sizing-2.shtml
http://www.poolspa.com/publications/sin/stories/pumps.htm

[Phillbo]

I live in Arizona.. my hayward runs when the pump is on. currently it's an after thought and is plugged in to the skimmer. THe pool has pop up heads on the bottom that do not work worth a darn. During the replaster I am having a decicated suction line run so it will draw through the skimmer while the hayward runs as well.

I'm not sure what to do with the pop ups in the bottom. Too expensive to run a bunch of return lines so most likely they will stay.

[mas985]

Didn't know about the floor cleaners. That changes the situation somewhat if you want to use them. You will need pretty high flow which will lead you toward a higher HP pump. You need to find out what flow is required for each cleaner and make sure the pump can supply the total. I would lean more towards a 2-speed pump so that you can have the high speed for cleaning and low speed for general circulation.