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Filter area, media performance, pump duty and heating load are not four separate decisions — each one narrows the next. These are the working charts we size against, with every assumption stated on the page rather than buried in a spreadsheet.
Every chart on this page is live. Enter your own figures and the curves redraw against them. Nothing here is a rule of thumb — each curve is drawn from a stated formula or a published dataset, and where a figure is estimated rather than measured, the chart says so on its face.
Enter the pool volume and the turnover you are designing to. That fixes the circulation flow, and everything after it is a trade: less filter area means higher velocity through the media, and higher velocity means the water leaves the filter dirtier. Move along the curve to see where a given area lands you.
| Pool type | PWTAG (UK) | MAHC (US CDC) |
|---|---|---|
| Competition pool, 50 m | 3–4 h | 6 h max |
| Public / hotel pool up to 25 m | 2.5–3 h | 6 h max |
| Leisure water over 1.5 m deep | 2–2.5 h | 6 h max |
| Leisure water 1–1.5 m deep | 1–2 h | 2 h max |
| Teaching / learner / training pool | 30–90 min | — |
| Hydrotherapy pool | 30–90 min | — |
| Children’s water 0.5–1 m deep | 30–75 min | 1 h max |
| Children’s water up to 0.5 m deep | 10–45 min | 1 h max |
| Domestic / private pool | 4–8 h | not covered |
| Diving pool | 4–8 h | 8 h max |
| Spa — commercial | 6 min | 30 min max |
| Spa — domestic | 15 min | not covered |
| Interactive water feature | 20 min | 30 min max |
PWTAG figures are Table 2 of the Code of Practice for the Management and Treatment of Swimming Pool Water, August 2019. MAHC figures are the maximum turnover times in the CDC Model Aquatic Health Code. PWTAG states a range to design within; MAHC states a ceiling not to exceed. Neither is enforceable in India, and where the two disagree the shorter figure is the safer basis for sizing.
Filtration area (m²) against filtration velocity (m³/hr/m²), coloured by the removal efficiency the selected media achieves at that velocity.
| Vessel diameter | Area each | Vessels needed | Installed area | Actual velocity | Removal efficiency | Clarity band |
|---|
Standard pressure filter diameters, and how many of each it takes to reach the area at the cursor. Because vessels come in whole numbers, the velocity a pool actually runs at is rarely the one it was sized for — the last three columns are the real figures.
The dataset behind the colour on chart 01, shown directly. Particulate removal efficiency falls as filtration velocity rises, and glass media stays ahead of silica sand at every velocity band — but the gap only becomes decisive once the medium-rate threshold is crossed.
Particulate removal efficiency vs. filtration velocity — glass media vs. silica sand. Hover over the chart for exact readings.
Sand-curve shape and the 25 m/h threshold reflect PWTAG's published filtration rate guidance (low-rate ≤10 m/h, medium-rate 10–25 m/h, high-rate 25–50 m/h; high-rate ≈10–25% as effective as medium-rate). Source: pwtag.org. Glass-media curve reflects directional industry consensus on finer particle capture, not a single controlled study.
Every rated flow figure in every catalogue is quoted at a reference head of around 8 m. Almost no pool runs at 8 m. Fix the head your system actually imposes, then read across: the curve is the horsepower needed to deliver each discharge at that head. This is why pump counts derived from rated flow under-deliver once installed.
Pump rating (HP) against discharge (m³/hr) at the selected head. Faint grey curves are the same relationship at 5, 10, 15, 20 and 25 m for comparison.
| Pump tier | Discharge at this head | Shut-off head | Rated point | Data confidence |
|---|
These are the points the curve is drawn through. A tier past its shut-off head delivers nothing and drops out of the curve entirely.
A pool's heat-up load is fixed by water volume and temperature rise, not by a rule of thumb. Enter the volume and the heat-up window, then read the required capacity at your ΔT. A 3°C-ambient equipment derating and a covered-outdoor-pool heat-loss buffer are already built in, so the number read off the curve is the nameplate rating to specify.
ΔT (°C) vs. required heat pump rated capacity (kW). Hover or tap to read the exact capacity at any ΔT.
These charts describe constraints, not quotations. Bed depth, hydraulic balance, pipe sizing and plant room layout all sit behind them, and a number that reads acceptable here can still be wrong on a specific site. If you are working on a scheme and want the figures checked against the actual drawings, we will do that.
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