Vessel 27.1 to 38.3 in · resin 10.0 to 20 ft³ · capacity ≥ 238 kgr/run · backwash ≤ 40 gpm
peak-month day = 18,000 gal (2.5× the 7,200 gal annual-average day) · effective hardness 226 mg/L · target 1-day run at peak
Click a row to select it. Duplex vessels are each full size, not half size. In alternating service only one is flowing and it must pass the whole flow. Two half-size tanks is the single most common duplex sizing error.
Three independent checks, never one status light. They measure different things and can legitimately disagree.
“Does the second tank cost me more salt?” No. Salt per kilograin delivered is 0.556 lb/kgr, set by dose and reserve, identical for all four arrangements. Same water, same hardness, same salt. What arrangement buys is continuity and flux control.
Sites, systems, and saved comparisons arrive with accounts. The result stays on screen either way.
How this works · three flows, each used exactly onceOpen +
Instantaneous flow sizes the vessel diameter against the flux windows (5 to 10 gpm/ft² green; below 4 is channeling, hardness leakage on a bed with capacity to spare). Peak-month average-day makeup sizes capacity and regeneration frequency, never the annual average; a heating plant’s January runs about 3× the mean. Annual-average makeup prices salt and regeneration water only, and never touches sizing.
Sources & assumptions: capacity curve, typical 8% DVB SAC data (verify vs. Purolite/DuPont sheet and cite); flux windows per standard ion-exchange practice; standard FRP tank dimensions with typical resin fills (confirm with supplier); backwash 5.0 gpm/ft² at 55 °F, temperature-corrected; regen duration default 1.5 hr (sanity-check vs. typical cycles); seasonal multipliers are starting estimates, compute peak month ÷ 12-month average from real data when you have it. The calculator estimates; the field measures.