Sizing a Water Softener – Calculator, Formula & Chart
If you are looking for a water softener, then you should make sure to understand the sizing for water softener. Generally 32,000 grain units ( 1 cubic foot of resin) is really good capacity for your home, but it is possible if you have a large family ( 6 or more), large house ( 41000 sq ft+) or very hard water ( over 16 grains).
Ideally water softener should be sized so that it does not generate any more often that every 3 days you waste water and salt, also not should go longer than 15 days before regenerating. 7 days b/w is probably best – especially when you water is coming from a well where iron is present.
Calculation for Sizing a Water Softener
- Multiply the number of people in your family times 70 (gallons of water used per day, national average).
- Multiply the answer by your water hardness in grains per gallon (to convert mg/l or ppm to grains, divide by 17.1). If iron is present, add 5 grains for every ppm (mg/l) of iron (iron MUST be dissolved iron – it appears clear from the tap but leaves reddish-brown stains).
- This is your “grains per day” number. Divide this number into each of the softener capacities until you find the best size.
Note: With Logix computer-control valve, it is possible to program it for more efficient use of salt by setting the capacity at a lower amount. For example, a one cubic foot softener has a peak capacity of 32,000 grains at a salt setting of 18.5 lbs. per regeneration. This provides 1729 grains of softening per pound of salt (32,000/18.5). You can program this for a capacity of 24,000 grains at a salt setting of 8.5 lbs. of salt. This would provide a more efficient 2823 grains per pound of salt, nearly doubling the efficiency. Granted, it will regenerate slightly more often, but since it only uses about $0.10 of water per regeneration, this is not really a major consideration. This being said, the following capacity options list both the peak and the efficient levels to make a better decision.
1.0 cubic foot of resin – 32,000 grain peak, 24,000 efficient
1.5 cubic feet of resin – 48,000 grain peak, 32,000 efficient
2.0 cubic feet of resin – 64,000 grain peak, 40,000 efficient
5 people in home, 10 grains per gallon hardness.
- 5 people X 70 gpd = 350 total gpd
- 350 gpd X 10 grains = 3500 grains per day
1 cubic ft. @ 24,000 grains / 3500 = 6.8 days between regenerations
1.5 cubic ft. @ 32,000 grains / 3500 = 9 days between regenerations
2.0 cubic ft. @ 40,000 grains / 3500 = 11 days between regenerations
The best choice would be the 1 cubic foot unit (closest to 7 days).
High Salt-Efficiency Water Softener Sizing Guide