Still confused about sizing cartridge filter to my system

[CGannon]

I've read the forum posts and stuff on the web but I'm still a bit confused by the way it's being explained.

I've got a 33.5k gallon pool, a 1 1/2hp Hayward sp2610x15 pump and giant sand filter that I'd like to swap out for a cartridge filter. And the piping is 2" PVC and about 30 feet of head (10' vertical from main drain, 20' horizontal).

Based on the the math, I'm coming out with a desired 8hr flow rate of ~69 gpm. However, according to the manual, the actual flow rate is 85gpm.

I'm looking at the Hayward Star Clear 90 cartridge filter which has a Flow Rating of
90 GPM and an 8hr turnover rate of 43200 gal. Which doesn't seem sufficiently "over sized" to do the job.

Or should I go with the Hayward Star Clear 120 Flow rate of 120 gpm and 8hr turnover of 57600 gal. Which, if I'm reading things right, IS sufficiently oversized to do the job.

Not married to these choices. So, if you have a better suggestion, I'm all ears.

TIA!

CG

 

[jblizzle]

Flow rate is not important to filter sizing. The pool size and season length are what is important. Determining head loss and flow rate is not nearly as straightforward as you seem to be trying to make it. Turnover rates are also meaningless and are more a function of the pump and not the filter anyway.

For a cartridge filter, the bigger the better.

For a pool your size, I would suggest a filter up around 450 sqft. What you are looking at are WAY too small.

 

[duraleigh]

Most folks that start with a big filter, really like it. What don't you like about your sand filter? I know that's not your question but it helps us to get lot's of anecdotal information about filters.

 

[CGannon]

For a pool your size, I would suggest a filter up around 450 sqft. What you are looking at are WAY too small.

Thank you for your reply! So, how do you come to 450 sq feet? What's the math I should be using?

@duraleigh: Sand filter is reaching end of life, broken laterals, sand needs replacing. Also, want to get away from backwashing as it runs into neighbor's yard. Old neighbor didn't care. New neighbor does. Need to repair/replace either way.

 

[jblizzle]

Go to the filter sizing section of this sticky: Hydraulics 101 - Have you lost your head?
You can see a minimum size for your pool volume that is assuming some turnover rate. Based on forum experience, we roughly double that size for Cart and DE filters just due to the hassle of cleaning them.

The filter recommendations I make are more based on a frequency of cleaning than on flow rates, etc. You can go smaller, but you will have to clean it more often.

(Note I have a different table that I use to look up filter sizes, I need to re-find the source of it as it is a little different than the link above).

 

[CGannon]

we roughly double that size for Cart and DE filters just due to the hassle of cleaning them...

Ah! Makes sense! Thanks again. Now considering Hayward Swimclear Cartridge Filter 425 Sq Ft..

 

[jblizzle]

That would be a better choice IMO

 

[duraleigh]

@duraleigh: Sand filter is reaching end of life, broken laterals, sand needs replacing. Also, want to get away from backwashing as it runs into neighbor's yard. Old neighbor didn't care. New neighbor does. Need to repair/replace either way.

Thanks, that makes good sense, too! Appreciate the input.