Methodology

Every calculator on this site shows its formula in a "see the math" panel. This page collects the sources and assumptions in one place.

The reference conversion (default numbers)

The conversion calculator's defaults come from a documented 15,000-gallon residential conversion: a 700 W single-speed pump running 10 h/day plus weekly chlorine was replaced with a variable-speed pump (80 W at scheduled speed) and a salt chlorine generator. Measured outcome: electricity $766.50 → $87.60/yr, chemicals $930 → $253/yr — $1,355.90 saved per year against $1,515 upfront, a 13-month payback. Your numbers will differ; that's what the sliders are for.

Salt dosing

Salinity in ppm is milligrams of salt per liter of water, so the dose is a pure mass balance: lbs = gallons × Δppm × 3.78541 L/gal ÷ 453,592 mg/lb. No lookup tables, no rounding to the nearest 500 ppm.

Pool volume

True geometry: surface area × average depth × 7.48052 gal/ft³. Round pools use π/4 × d², ovals use the ellipse area π/4 × L × W. For constant-slope bottoms the midpoint average depth is exact; hopper bottoms will read slightly high (a safe direction for dosing).

Pump energy

kWh/yr = W ÷ 1000 × h/day × 365, priced at your utility rate. The large savings from variable-speed pumps follow the pump affinity law — shaft power scales with the cube of impeller speed — so moving the same daily water volume at lower RPM for longer costs a fraction of the energy.

What we deliberately leave out

• Inflation and financing on payback math (add ~1 month per year of payback at today's rates).
• Salt-cell replacement (~every 3–7 seasons, $200–$700) — it lengthens long paybacks slightly.
• Regional water chemistry effects on cell life; consult your cell manual.