Understanding Water Softener Grains Capacity
All over the internet, in every big box store, and at the local Mom & Pop water treatment store you'll find water softeners that are described by their grains capacity. To those who aren't in the industry this is a foreign term, and it's often quickly glossed over by salespeople who probably don't understand its implications in choosing a water softener that's sized correctly for their customer.
Grains capacity is simply the amount of hardness that can be removed by a water softener before it must regenerated. Water softeners are a type of ion exchange technology. Ions of calcium and magnesium (aka 'hardness') are grabbed onto by the water softener, and exchanged for ions of sodium. The grains capacity of a softener is the weight of calcium and magnesium hardness compounds that can be removed from the water before the softener is saturated and must be regenerated. A grain is defined as approximately 65mg - about the weight of a cereal grain such as wheat or rye.
What is so confusing about grains capacity, and why it really is not a good way to talk about water softener capacity, is that the grains capacity of any given water softener is variable. That's right - a water softener described as a 32,000 grain softener could also be called a 20,000 grain or 25,000 grain softener. But how?
Well, the assumption made by consumers, and understandably so, is that the grains capacity of a softener refers to the amount of resin it contains in the softening tank. Surely, the logic would go, that the amount of softening that a water softener can achieve must be dictated by the amount of resin, right? What is unfortunately never, or very very rarely, talked about by dealers and consumers alike, is that the amount of resin in the softening tank of a softener is only half responsible for determining the grains capacity of the softener.
It turns out the the amount of softening that a given quantity of resin can achieve is a function of the amount of resin in the softening tank and the amount of salt that is used when the softener is regenerated. To illustrate this point, we'll look at a very commonly sold water softener - a 32,000 grain system:
A 32,000 grain water softener is much more accurately described as a 1.0 cubic foot water softener. This is because the softener is built with 1.0 cubic feet of resin. A 1.0 cubic foot quantity of resin can be regenerated with various differing amounts of salt, to achieve different grain capacities:
6 pounds of salt = 20,000 grains
9 pounds of salt = 25,000 grains
15 pounds of salt = 32,000 grains
So why is a 1.0 cubic foot softener called a 32,000 grain system? Well, at some point along the line the marketing people that make and sell softeners decided that 32,000 sounds a lot better than 20,000 or 25,000. The bigger the number, the better the softener, right.
What gets lost in this approach is the efficiency rating of the system. If we return to our example above you'll see that to achieve 32,000 grains of softening from a 1.0 cubic foot softener, we need to use 15 pounds of salt. So, the amount of softening that can be achieved by each pound of salt used is 32,000 grains / 15 pounds = 2133 grains per pound of salt. To maximize the efficiency of a softener we want it to remove the maximum number of grains for the minimum amount of salt used. A much more efficient way to regenerate that same 1.0 cubic foot softener, is to use 6 pounds of salt to generate 20,000 grains of capacity: 20,000 grains / 6 pounds = 3333 grains per pound.
So, should this system be called a 20,000 grain or 32,000 grain system? You see the dilemma. There are two big problems with calling this system a 32,000 grain system. The first issue is that all of the 'water softener sizing' calculators that exist on the internet assume that softeners will be set up based on the maximum grains capacity that the unit can generate. This means that consumers buy a softener and are forced to operate the softener in the least efficient way possible.
The second possible outcome is that a consumer buys a softener based on it's maximum (and highly inefficient) potential grains capacity, and then realizes after purchase that in order to run at that max capacity the softener is going to have to use a massive amount of salt. At that point, the consumer could make changes to the programming of the softener to make it run more efficiently, but would then have a softener that is undersized (capacity wise) for their home.
So what's the solution to this? The solution is to only buy a water softener that states its capacity and it's efficiency. Don't purchase any softener that can't achieve at least 3333 grains of softening per pound of salt. And ideally, look for a very high efficiency softener that can achieve 5000 grains per pound of salt like the high efficiency Aquatell Citymaster softener.