Water Softener Sizing Calculator

Inputs

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Occupants, residents or equivalent fixture users for a usage estimate.
Average softened water use per person per day. Use meter data for better sizing.
gal/person/day
Raw water hardness in grains per gallon. 1 gpg is about 17.1 mg/L as CaCO3.
gpg
Dissolved ferrous iron. Ferric iron, bacteria and fouling need separate treatment.
mg/L
Rule-of-thumb added hardness per mg/L of dissolved iron.
gpg per mg/L iron
Desired service interval before regeneration.
days
Extra grain capacity held for high-use days and meter uncertainty.
%
Expected peak softened-water flow through the softener.
gpm
Approximate continuous service-flow allowance per cubic foot of resin.
gpm/ft^3
Approximate usable capacity per cubic foot at the selected salt dose. Dealer nominal ratings are often higher than efficient operating capacity.

Results

Default result
Edit inputs
Recommended resin volume(V_resin)
1.5ft^3
Pass

capacity and regeneration interval govern the resin size

Also computed

Usable grain capacity(C_use)Pass36,000grains

24,000 grains/ft^3 usable at the selected salt setting

Estimated regeneration interval(d_actual)Pass9.259days

Compensated hardness(H_c)Pass16.2gpg

measured hardness plus iron allowance

Daily grain load(G_day)3,888grains/day

Daily softened water use(Q_day)240gal/day

Gallons between regenerations(G_regen)2,222gal

Water softener sizing preview: 1.50 cubic feet resin, 36000 grains usable capacityWater softener sizing previewCapacity, service flow and regeneration interval from hardness load.resin tank1.50 ft^3Sizing demandCapacity-driven resinFlow-driven resinRegeneration interval9.3 days at entered water useUsable capacity36,000grains at selected salt settingSalt per regen12.0 lb39.4 lb/month estimateCompensated hardness 16.2 gpg; service flow capacity 12.0 gpm.
Method notes 3 notes
  • Compensated hardness is H_c = hardness_gpg + iron_mg/L x iron allowance. Daily grain load is H_c x gallons/day.
  • Resin is sized by both grain capacity and service flow, then rounded up to a common resin volume. Usable capacity varies strongly with salt dose.
  • This is a sizing screen for softener capacity, not a full water-treatment design. Verify raw water chemistry, iron form, manganese, tannins, pH, turbidity, chlorine, control-valve pressure drop, drain flow, brine settings and local plumbing requirements.

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