Pool Filter & Pump Sizing Question?

[zooba72]

I have an 18 x 36 T shaped pool, approximately 42K Gallons. I currently have a Purex Triton FNS Plus 180007
36 sq. DE Filter ... with a 1.5 HP Hayward Super Pump. I'm considering replacing my filter with a Nautilus NS 36 Stainless Steel Filter. Any comments on whether that filter is too small for this pool? I have both filters at my disposal and prefer Stainless Steel.

Any thoughts on this? Thanks in advance.

[mas985]

For a 42k gallon pool, NSF recommendations are for a 60 sq-ft filter. However, a 1.5 HP Superpump should not deliver more than 70 GPM on 2" plumbing, which means that you could probably get away with a 36 sq-ft filter but to make sure that you are below the 2 GPM/sqft limit, I would leave at least 25% margin and go with a 45 sq-ft filter.


But just to make sure, can you describe the following:

Height of pump relative to the water level
Suction pipe diameter (e.g. 1.5" 2", 2.5")
Number of individual suction pipes from the water to the equipment
Average length of suction pipes
Number and type of suction side valves
Filter PSI reading at the desired valve settings and pump's highest speed setting
Heater - yes or no

[zooba72]

Thanks for the response. The reason I'm asking is because I've always preferred the Stainless Steel filters. For some reason about 10 years ago, all of the pool service companies seemed to have replaced the stainless steel Nautilus with the FNS filters. I never understood why? ... It almost seemed like thievery. Anyway, I've been looking for a used Nautilus NS filter and finally found one for a reasonable price. According to the manual the NS36 will filter 43,200 gallons in 10 hours, where my current FNS filter does 43,200 in 8 hours. I was thinking just run the pump longer and I would be good. Before starting to type this response I learned that the used Nautilus NS 36 has a few tears in the grid system, so I think I'm going to pass on it anyway. I agree that the NS48 would be ideal. Thanks for the response.

- I would estimate the pump to be between 18" - 24" above the pool waterline.
- Pipe diameter is 2"
- Suction Pipes (I have two skimmers and a main drain feeding water to the filter system). I would estimate them to be an average of 20FT.
- I currently do not have a two speed pump, but filter pressure is usually between 18 - 20 PSI
- No heater

[mas985]

Filter pressure is a little high which indicates fairly high return head loss so I am estimating flow rate somewhere around 53 GPM. You could get away with the a 36-sqft filter but a larger filter is going to need less cleaning which is always a plus.

As for materials, fiberglass-reinforced polypropylene is strong, stands up pretty well to chemicals and it is cheaper than SS so I think that is why they don't make many SS filters anymore.

[Orion]

Zooba, I tried to reply about the stainless setup, but my post never appeared...not sure why...

[zooba72]

No problem. I decided to pass on that unit because it had some cracked grids. I'm still looking for a used Nautilus NS48. Thanks