Household water softeners are rated by the number of grains of hardness they can remove through a specific volume of resin in the tank, and the amount of salt needed to regenerate the resin.
Many retailers and product websites provide conflicting information about how to calculate the appropriate size of softener for your household needs. Note that most, if not all, retailers in North America quote U.S. measures for weights and volumes.
To find the right size of softener for your household you’ll need two things:
Multiply your household’s average daily water use as calculated in step one, by the grains of hardness in your water found in step two. The full formula to calculate your daily hardness removal requirement is:
Number of people in your home
Average indoor daily water consumption per person
Grains of hardness in your water
Grains of hardness to be removed daily
Most suppliers recommend people buy a water softener that could potentially remove hardness from the water for seven days before needing to regenerate. Simply multiply your daily hardness removal requirement by seven to calculate the suggested water softener size. Although water softener sizes vary, the table below gives some of the more typical sizes of softener available for a range of daily grain requirements.
|Daily Grain Removal Requirements||Suggested Softener Size|
|0 – 3,500 grains per day||24,000 grain capacity|
|3,501 – 4,500 grains per day||32,000 grain capacity|
|4,501 – 5,750 grains per day||40,000 grain capacity|
|5,751 – 6,850 grains per day||48,000 grain capacity|
Research shows that some ion exchange water softeners work more efficiently than others. The Region of Waterloo and City of Guelph work with experts in the field to develop higher performance benchmarks for water softeners in order to reduce salt, water and energy use. You can make an informed decision about which water softener to buy by following these steps:
This is a voluntary certification that states, when the softener is set to operate efficiently, that it will remove a minimum of 3,350 grains of hardness per pound of salt used. At the same time, it will not use more than 5 U.S. gallons of water per 1,000 grains of hardness removed. This should be considered a minimum standard. Many softeners on the market are even more efficient.
To meet the NSF/ANSI 44 Performance Standard, suppliers must make salt efficiency information available with the machine. This information can be found in the owner’s manual, on a separate sheet of paper, or on the internet. Below is an example of how the performance information about a softener may be presented:
Model No.: XXXXXXX
A. Capacity – Grains: @15 lbs/cu.ft: 30,000
B. Capacity – Grains: Factory @10 lbs/cu.ft: 27,500
C. Capacity – Grains: @6 lbs/cu.ft: 20,000
The longer a water softener is allowed to run before regeneration, the less efficient it becomes. This happens because it takes proportionally more salt to recondition exhausted resin beads. The above example shows how much salt the softener would use at three different settings. You’ll want to select your water softeners most efficient setting for maximum savings. Here’s what these settings mean
A. Capacity – Grains: @15lbs of salt/cu.ft: 30,000
This means it will take 15 pounds of salt to regenerate a 30,000 grain capacity water softener (containing one cubic foot of resin) if it were to run to complete exhaustion. If you divide 30,000 grains by 15 pounds, you’ll get a removal capacity of 2,000 grains per pound of salt used. At this setting, the softener will not meet the minimum requirement of the NSF/ANSI 44 Performance Standard.
B. Capacity – Grains: Factory @10 lbs/cu.ft: 27,500
The softener (with one cubic foot of resin) comes factory set to regenerate with 10 pounds of salt after it has removed 27,500 grains of hardness. At this setting, the efficiency has improved to 2,750 grains of hardness removed per pound of salt used, but it still does not meet the NSF/ANSI 44 Performance Standard.
C. Capacity – Grains: Factory @6 lbs/cu.ft: 20,000
This setting is the most efficient one for this softener. The softener (with 1 cubic foot of resin) is set to regenerate when 20,000 grains of hardness has been removed, and will require 6 pounds of salt. This equates to a removal of 3,333 grains of hardness per pound of salt used. This setting would pass the NSF/ANSI 44 standard because it is within 10 per cent of the target 3,350 grains removal per pound of salt. Note that at this setting, the softener will regenerate more often and will not run the resin to exhaustion.
Unfortunately, the NSF/ANSI 44 standard does not require suppliers to give the regeneration water consumption figures and this data is often missing from published information. This is something the Region of Waterloo and Guelph are asking NSF to change. In the meantime, you can at least compare the salt efficiencies of water softeners.
The Region of Waterloo and City of Guelph do not endorse specific brands of water softener, or provide a list of the best performers on this web site. For a list of NSF–certified water softeners, go to www.nsfconsumer.org or call 1-800-673-8010.
Now be sure to set your water softener to its most efficient setting!
To select the right salt, read about how water softeners work.