3 Steps To Sizing A Water Softener


What Is A Water Softener?

The minerals that are responsible for causing hard water are generally not hazardous to health but are in fact essential nutrients. These minerals commonly include calcium and magnesium but may also include iron. However, they can cause dry skin and brittle or dry hair and nails. They also result in the build-up of mineral deposits in water pipes, faucets and drains and can cause serious damage. These deposits cause blockages that can be difficult to remove.


A water softener is a unit that is attached to the water supply in order to remove ions or minerals that are responsible for causing hard water. In effect, a water softener softens hard water. However, in order for the water softener to be effective, there are many factors that need to be taken into consideration. One of the most important of these is the size of the unit.


Why Is It Important To Size A Water Softener?


It all comes down to efficiency. A water softener that is too small will require much more salt to be effective than a unit that is properly sized. An efficient water softener should require an average of 300 pounds of salt in order to operate per year. An improperly sized unit can however use up to 2,000 pounds of salt in a year.


Less salt means less cost and also saves on the time and effort it takes to replace the salt regularly in order to ensure a constant flow of soft water. Efficiency is also important to the environment as less salt is expelled during the water softening process. Inefficiency may lead to a unit that malfunctions or that is more prone to wear and tear. An efficient unit that is sized correctly should provide an extended period of operation without failing.


How To Size A Water Softener?

There are 3 main calculations that are needed in order to determine the correct size water softener for a specific home:

- The size of the property that the water softener unit will be serving, how many people are living in the household and each person's average water consumption to calculate the total water consumption.

- The concentration of mineral deposits in the water to determine the grade or hardness of the water.


1. Calculating Average Water Consumption

The simplest way to calculate average water consumption is to look at a monthly water bill. The consumption for the entire household should be reflected in the bill. It is recommended to use the following calculations to determine an average:

  1. Add up the water consumption for each month in a year reflected on the water bill. Divide the amount by 12 months to determine the average household water consumption.
  2. If it isn't possible to use 12 months of water bills, simply divide the sum of the amount reflected by the amount of water bills that are available. For example, if there are 8 water bills, add the consumption on each bill together and then divide the amount by 8 to determine the average. It is not recommended to use this calculation for a period of less than 3 months and it is ideal to calculate an average over 12 months.
  3.  If water bills are not available, then the calculation can be made according to the size of the property and the amount of people in the household. In general, each person uses 75 to 80 gallons of water a day. So if there are 5 people a day, 80 gallons of water multiplied by 5 people equals a consumption of 400 gallons. Multiply this figure by 365 days and it should provide an estimated annual average water consumption.
  4. Taking daily water meter readings can also help determine how much water the household consumes. Do this for a period of 1 month to arrive at a more accurate calculation. Add each daily reading together and divide by the amount of days over which readings were taken then multiply by 365 days to calculate the average water consumption for the household for one year.

Once the average annual water consumption has been determined, simply divide the amount by 365 (days in the year) to arrive at the average daily water consumption.

* The most accurate calculation is measuring water consumption for a period of 12 months. Household water consumption may increase in the summer months and calculations that are made in the colder months may not be as accurate as taking every season into consideration.


2. Calculating Water Grade Or Hardness

There are a variety of different ways in which to test for hard water. The DIY options will determine whether hard water exists or not but will not provide a grade for the water. There are home-testing kits that can be purchased for a nominal cost but these are not always accurate.

It is highly recommended to have water laboratory tested in order to provide an accurate grade to properly size a suitable water softener. There are a range of different companies that provide water testing.


Depending on the company used, the test results may be in milligrams per liter. However, the water softener industry uses a different measurement called GPG which measures the grains per gallon of water. If the results are reflected in mg/L, simply divide the amount by 17.1 to arrive at the GPG measurement.


With City Water, lab testing is not necessary and the grade or hardness level should be available from the local water utility company. Testing is normally conducted once a year and published online where results can be viewed. It is recommended to check the readings or measurements regularly to ensure that there have been not significant changes relative to location.


It is very important to have accurate water hardness or grade readings. Not only will it determine a suitable size water softening unit but it will also need to be programmed into the water softener in order for it to operate optimally and efficiently. Guessing the grade will lead to insufficient water softening and inefficiency.

- A GPG of less than one relates to soft water.

- A GPG of between 1 and 3.5 is slightly hard.

- A GPG of between 3.5 and 7 is moderately hard.

- A GPG of between 7 and 10.5 is hard.

- A GPG of over 10.5 is very hard or like a stone.

It is generally recommended to get a water softener for water that registers anywhere from slightly hard to very hard.


3. Calculating Water Softening Requirements

Once an accurate calculation of average daily water consumption and measurement of water hardness has been determined, these two amounts need to be used to determine the water softening requirements for the household.

Simply multiply the GPG by the average daily water consumption for the household. For example:

GPG = 10

Average daily water consumption = 400

Water softening requirements = 10 x 400 = 4,000

In essence, the water softener will be required to remove 4,000 grains of minerals every day.

These 3 calculations are actually very simple. However, it is important to reiterate the importance of accuracy and avoiding guesswork. Also be aware of online calculators that only use one of the two factors to calculate the daily water softening requirements.


How To Select A Suitably Sized Water Softener?

Water softeners are generally designed to regenerate every 7 days or once a week. There are two main reasons for this:

- To reduce wear and tear on the valve and other working parts of the water softening unit.

- To lower water consumption that takes place during regeneration. A water softener uses on average 50 gallons of water when it regenerates which equates to around 200 gallons per month on a weekly basis.

In order to determine which size water softener to select, it is necessary to convert the daily water softener requirements into a weekly measurement. Simply multiply the daily requirement by 7 which will provide the amount of grains that the water softener regenerates over one week.

Using the example above where the daily water softener requirement was 4,000, the weekly requirement will be 24,000 for the household:

Weekly water softener requirement = 4,000 x 7 = 24,000

The household will therefore require a minimum of 24,000 grain system water softener.


Water Softener Grain System Categories

Water softeners commonly come in 24,000, 32,000, 48,000 and 64,000 grain systems. It is recommended to select a grain system that is in excess of the weekly water softener requirement.

In the example above where the weekly water softener requirements are 24,000, a 24,000 grain system should be sufficient. However, it may be recommended to select the 32,000 grain water system for greater efficiency. There are 3 main reasons for this:

  1. The salt that is required to regenerate a 24,000 grain system equates to 27 pounds. The 32,000 grain system should therefore effectively require 36 pounds of salt per regeneration. However, the 32,000 grain system only requires 6 pounds of salt to regenerate 20,000 gallons of water making it far more efficient than the 24,000 grain system.
  2. Although the 32,000 grain system is slightly more costly than the 24,000 system, the savings in salt costs will quickly make up the difference and continue providing savings well into the future.
  3. The 32,000 grain system is sufficient to meet the water softening requirements of most households.

Water Softener Capacity

Last but not least, it is important to understand a little more about the capacity of a water softener unit in order to determine its efficiency.

The capacity is measured by the amount of softening resin (in cubic feet) in the unit relative to the amount of salt that it requires.

0.75 cubic feet resin = efficiency capacity of 15,000 grains.

1 cubic foot resin = efficiency capacity of 20,000 grains.

1.5 cubic foot resin = efficiency capacity of 30,000 grains.

2 cubic foot resin = efficiency capacity of 40,000 grains.

In order to achieve the greatest efficiency from a water softening unit, is therefore necessary to take into account the capacity relative to the cubic feet of resin.


So in the example that was used above for water softening requirements of 24,000 grains per week, it may be best to select a unit with between 1 and 1.5 cubic feet of water softening resin.

It is highly recommended to get an expert to provide assistance in calculating the water softener requirements for a specific household that would provide the greatest efficiency. However, it is just as important to ensure that all the above-mentioned factors are taken into account in selecting the most suitable system.

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