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Selecting the Correct Size Water Softener

Reserve capacity

Our softeners are factory set to normally regenerate at 2:00 AM (although you can change this). So, if there is some water usage at (for example) 2:15 AM, and the softener determines that a re-generation is necessary, the unit will not regenerate until the following night at 2:00 AM. You need to make sure that in this case you have the extra capacity (reserve capacity) to carry you through the next day, and also have a little extra capacity for when the softener resin loses some of it's fresh activity years down the road. For this reason the industry standard is to recommend that you determine the size of your water softener using a value that is 20% less than it's actual capacity. Use the values in the reserve column below to size your softener.

Actual Softener Capacity

With 20% Reserve

24,000 grain capacity


32,000 grain capacity


48,000 grain capacity


64,000 grain capacity


Sizing your softener

Water hardness can be reported in "grains per gallon" (gpg), "parts per million" (ppm) or "milligrams per liter" (mg/l). Most of the industry calculates softener size using gpg. You can divide ppm and mg/l by 17.1 to obtain your hardness value in grains per gallon.

You will also need to account for the iron and manganese in your water, and a quick way to get this value is to multiply your iron and manganese concentration (in ppm or mg/l) by a factor of 4. Add this number to the hardness value you determined above. The resulting total value is similar to a "compensated" hardness value, and will better serve to size your softener.

In the example below we will use 4 people in the home and a hardness value of 10 grains per gallon, and iron concentration of 2 ppm.

Multiply 4 people in the home x 75 gallons water usage per person per day x (10 grains hardness + (2 ppm iron x 4)) = 5,400 grains of hardness to be removed per day. So with a 32,000 grain system, set capacity would be about 26,000 grains (20% lower than actual - reserve capacity), and a metered unit would regenerate approximately every 5 days (26,000 divided by 5,400), which is acceptable.

Use the formula above to adjust for the number of people actually living in your home, and your specific water hardness.

With normal to low levels of iron in your water, you can size your softener to regenerate between every 5 to 10 days. With higher levels of iron (5 mg/l and higher) and manganese (1 mg/l and higher), it's better to size a system to regenerate more frequently, in order to keep the resin bed free of accumulated deposits. In this case, a regeneration every three to five days may be required. If you have very high iron levels in your water, please contact us by email or telephone for a sizing recommendation.

Visit our General Information  page for more information on factors that affect water softener performance

Typical Specifications for CAI Residential Softeners RESIDENTIAL SOFTENERS








7" DIA. X 44"

18" DIA. X 33"




8" DIA. X 44"

18" DIA. X 33"




10" DIA. X 54"

18" DIA. X 33"




12" DIA. X 52"

18" DIA. X 33"



* Unit size refers to softening capacity using highest typical salt usage setting for unit regeneration cycle. Unit capacity varies with salt consumption. Increased capacities can be achieved by using higher salt consumption and/or more frequent regeneration intervals. Sizing and salt consumption is approximate, please E-mail with any questions.
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