Helpful Guide To Water Softener Sizes. Selecting A Softener To Match Your Home Conditions.

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Ion-Exchange Water Softeners Sizes

Salt-based ion-exchange water softeners are classed in sizes according to the capacity of the resin beads to remove ‘grains’ of water hardness.

Each grain of water hardness is equal to 17.118ppm (or mg/L), and each cubic foot of standard 8% cross-link resin beads is generally rated at being able to remove 32,000 grains of water hardness. In metric terms, each liter of resin beads can remove 1,130 grains, or 19,344.55milligrams, of water hardness ions.

How Much Should A Resin Bean Last?

Resin beads for water softeners are usually supplied in units of cubic feet or half cubic feet, although smaller quantities can be purchased. Resin beads should last for between 8 and 15 years before they need to be replaced, so if you have problems with your water softener within that period you should look at issues such as chlorine and iron levels in your household water supply.

These can be avoided when you re-fill your ion-exchange tank with fresh resin beads by either using an iron treatment on the resin on a once-yearly basis, or installing a pre-filter to reduce levels of other chemicals such as chlorine. Using 10% cross-link resin beads will increase capacity to remove iron.

Symptoms of the loss of capacity in the resin beads include a loss of water pressure, a salty taste to the water after re-filling the brine tank with salt, or small particles of resin flowing out of faucets with the water.

These can be avoided when you re-fill your ion-exchange tank with fresh resin beads by either using an iron treatment on the resin on a once-yearly basis, or installing a pre-filter to reduce levels of other chemicals such as chlorine.

Using 10% cross-link resin beads will increase capacity to remove iron. Symptoms of the loss of capacity in the resin beads include a loss of water pressure, a salty taste to the water after re-filling the brine tank with salt, or small particles of resin flowing out of faucets with the water.

Ion-exchange water softeners are available in a wide range of sizes. Standard water softener capacities are 32,000 grains, 48,000 grains, 64,000 grains, 80,000 grains and 96,000 grains of water hardness removal, implying one cubic foot (1 cuft), 1.5cuft, 2cuft, 2.5cuft and 3cuft of resin beads respectively.

How Big Should Be My Water Softener?

As was noted in earlier sections, the average volume of water used per household member in the USA is estimated to be 75 gallons (284 liters) per day.

From this figure, multiplied by the number of people in the household and the water hardness in grains per gallon (gpg), you will be able to determine the quantity of grains of hardness per day that needs to be removed from your household’s water supply. 

Multiply the resulting figure by 7 days, and you will know what size your water softener will need to be in order to regenerate at the recommended rate of once per week.

​For example, a 5-person household with 25gpg of water hardness will need to consider a system of at least 5 x 75 gallons x 25gpg x 7 days = 65,625 grains capacity.

Bear in mind, however, that regeneration generally only re-activates about 94% of the resin beads’ capacity, so the required capacity to achieve consistent removal of 65,625 grains would be close to 70,000 grains, and this requires massive amounts of salt.

Using the efficiency factor discussed earlier, the grain capacity will need to be increased by 38% to cater for regeneration losses. Thus, the recommended water softener size for the example would be 1.38 x 65,625 grains = 90,562 grains.

So, the recommended size of water softener to be purchased for the household in the above example would be a 96,000 grain system (using 3 cubic feet of resin beads).​

Dual Tank or Portable Water Softener?

As was also discussed elsewhere, it is possible to purchase dual tank systems to avoid having to bypass the softener with hard water during the regeneration cycle.

​Some water softener suppliers do, however, manufacture systems that use non-standard capacities such as 20,000 grains, 30,000 grains and 40,000 grains, as well as 22,000 grains, 31,000 grains, 34,000 grains, and 42,000 grains.

Portable water softeners designed for use in RV’s are available in sizes such as 15,000 grains and 16,000 grains (half a cubic foot).

Salt-free water conditioners are usually rated in expected lifetime periods such as 4 to 6 months or two years, or in anticipated conditioning volumes, such as 600,000 gallons, or a combination of the two.

These are extremely generalized figures, however, and they do not take into account the number of people in a household or the hardness levels of the water.

For instance, the filter cartridge for the 3M Aqua-pure AP904 (buy on Amazon) water filter with scale inhibitor is stated as needing to be replaced “once a year or after 100,000 gallons, however, the filter may need to be replaced sooner depending on your water quality”.

So, What's The Verdict?

Whatever your water softening needs, you will be able to find a system that will cater for you and your household.

Whether you live in a small household or a large mansion, whether on a boat in a marina or travelling the country in an RV – there are so many types and sizes of water softeners, you never have to do without softened water.