Pool Pump & Filter Calculators

The pool industry's filtration story is mostly wrong in the same way, and the four calculators in this cluster correct it in sequence. You don't need to run your pump eight hours a day. Bigger isn't better for pumps. Filter media don't compare on raw square footage. And the textbook 75 % variable-speed saving isn't real. Reading the hub in order takes about three minutes and saves owners a pump replacement they didn't need.

The arc starts at run time, because that's where most over-spending happens. The conventional answer is “one turnover a day” — about eight hours for a typical pool — and the conventional answer is wrong on its own terms: one turnover doesn't filter 100 % of the water. It filters about 63 %, by the exponential mixing law (1 − e⁻ⁿ), the same law that says you can't fully clear a stirred tank in finite time. Most pools at one turnover with adequate chlorine stay clear. Most pools running eight hours are wasting most of those hours.

The sizequestion follows, and it's where the industry's horsepower habit causes most of the cost. A pump doesn't deliver its nameplate flow; it delivers the operating point — where the pump's curve crosses your plumbing's resistance curve. Bigger pump barely helps: +18 % HP only delivers +9 % more flow on the same pipes. But bigger pipe wins twice — +15 % flow and less water-power — because Hazen-Williams friction scales with pipe diameter to the 4.87 power. The field sells pumps; the physics sizes to the system, and usually smaller.

The filter question is the mirror image — same site, opposite truth. Where a bigger pump is usually worse, a bigger filter is genuinely better: more area means slower flow through the media, finer particle capture, and longer cycles between cleanings. The integrity wedge here is the 48× area spread between sand and cartridge at the same flow — both correctly sized, by completely different rate physics — which is why filter-shopping by raw square footage is the universal mistake the calculator corrects.

The costquestion closes the cluster. A variable-speed pump's saving is real but not 75 %. Two corrections stack: real pipe friction is flow^1.852 not flow², capping the saving at 72.3 %; and static head — the gravity lift the pump can't avoid — doesn't scale with flow, pulling the real saving to about 60 % on a typical pool. Still enormous: a $32 monthly pump bill drops to $13. Two-corrections honest, not marketing magic.