How to size a water softener

2006-02-28T13:01:00.000-08:00

When choosing a water softener, you must know your water analysis, i.e. hardness levels, dissolved iron and or manganese. Hardness is usually measured in "Grains per gallon", and iron and manganese is usually measured in "Parts per million". Since most softeners are rated by "grain capacity" it makes everything much easier to understand when sizing a system.

Iron and manganese (if any) also has to be taken into consideration when sizing a softener. Since these two are 3 times harder to remove than hardness, the standard rule of thumb is to multiply the iron content times three, then add it to the hardness which is "compensated hardness"

You must also know how much water you will use per day, or at least estimate this based on how many people live in your home. 75 gallons per person per day is standard.

The idea is to choose a softener that will not have to regenerate too often, but not too infrequently. A regeneration every 3 to 6 days is ideal.

Lets say you have a family of 4: 4 people x 75 gals per day= 300 gallons per day usage

Lets say you have 20 grains of hardness and no iron.

20 grains of hardness x 300 gallons = 6000 grains of hardness removal per day

In this case you would want at least a 32,000 maximum rated softener set to yield 24,000 of usable capacity. ****This is where it can get confusing. Manufacturers usually never set up a system to operate at maximum capacity because it's less salt efficient to do so. The capacity is dictated by the salt dosage used when the system regenerates.

For example: (With 1.0 cubic feet of water softening resin)
15 pounds of salt will yield about 32,000 grains of hardness removal (2133 grains/pound)
10 pounds about 27,000 (2700 grains/pound)
8 pounds about 24,000 (3000 grains per pound)
6# about 20,000 (3333 grains/ pound)

So you see how we actually get a higher return of grains of hardness removed per pound of salt with the lower salt setting?

You really want to be in the 3000 range and above for the best salt efficiency.
If you would rather skip all that, here is a link to a "cheat sheet" for sizing a water softener borrowed from www.softwaterdeals.com scroll down the homepage to view the sizing chart.

water-softeners

How to size a water softener