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Calculate required ion-exchange water softener grain capacity based on household family size, water hardness in grains per gallon (GPG), and iron content.
To size a water softener: multiply household members by 75 gallons/day to get daily usage, multiply by compensated hardness (GPG + 5 per PPM iron) to get daily grain removal, and multiply by 7 days for weekly capacity. A family of 4 with 15 GPG hardness and 1 PPM iron produces 6,000 grains of daily hardness, requiring a 48,000-grain water softener.
Adjust inputs for real-time results
Test kit reading. 1 GPG = 17.1 PPM / mg/L.
Add 5 GPG per 1.0 PPM of dissolved clear-water iron.
Recommended Softener Capacity
Note: Sizing for a 7-day regeneration cycle prevents bacterial fouling and maximizes salt efficiency.
Hard water scaling destroys heating elements and cuts tankless water heater efficiency by 30% in just 18 months.
Common questions regarding this calculation and code compliance
A family of 4 with moderate to hard water typically needs a 32,000 to 48,000 grain capacity water softener.
