Softener Grains Capacity vs Cubic Feet of Resin
There are two ways to describe the 'capacity' of a water softener. Historically, softener capacity has been described in Grains Capacity which is a description of the amount of softening that a water softener can accomplish, before it needs to regenerate. The other way of describing water softener capacity is by Cubic Feet of Resin. This is a description of the volume of resin the softener is built with. The more resin it's built with, the more softening it can accomplish before needing to regenerate.
So which way is the RIGHT way? To answer this question, we need to dive in a little deeper. But first, a quick lesson on how water softener resin is regenerated:
When a water softener regenerates (aka recharges) salt brine is pushed through the resin bed. This causes the resin to release the trapped hardness minerals and prepares it to do more softening. It's very important to note, that the amount of salt that is used to regenerate the resin, determines how much softening capacity the recharged resin will have.
The Grains Capacity method of describing water softener capacity fails to show that in order to achieve the stated capacity (32,000 / 48,000 / 64,000 etc) the softener needs to use an enormous amount of salt. In other words, the stated grains capacity numbers are the absolute maximum that the resin can deliver, and to achieve this max capacity, the softener needs to use the maximum amount of salt. Buying a water softener when they're described like this, will obligate the user to operate the softener in the least efficient manner possible. This means much more salt to buy, use, and discharge.
The Cubic Feet of Resin capacity-naming method simply looks at how much resin the softener is built with. It allows a much more transparent comparison of one softener to another because there's no interpretation required. It's the way that all softeners should be described, and it's how we do it at Aquatell.
However, knowing the cubic feet of resin doesn't tell us anything about how much softening the machine can accomplish. This is where the Softener Efficiency Rating or SER comes into play. The SER describes how much softening the machine can accomplish per pound of salt consumed. You can learn more about SER in Aquatell's Ultimate Guide To Choosing A Water Softener.