What Size Water Softener Do I Need?

C.E. Larusso
Written by C.E. Larusso
Updated December 8, 2021
Father and little son doing laundry together
Photo: wavebreak3 / Adobe Stock

Highlights

  • Determine your family’s weekly softening requirement and opt for a system with a suitable grain capacity 

  • Most 3–4 person households opt for a 32,000 GR unit

  • With programmable systems, grains/pounds of salt is a more reliable indicator than peak grain capacity

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Goldilocks sometimes gets a bad rap, but her approach is necessary when you’re sizing a water softener. You need a device that has just the right capacity; too little and it could lower the water pressure in your home, wear out quickly, and fail to soften the water to the extent you require; too much and you’ll end up spending more money for a less efficient system. 

Water softeners serve to excise the scourge of hard water from your family’s pipes and taps. The majority of models use a process of ion exchange to remove calcium and magnesium—the minerals that make water hard—and swap salt or sodium in their place. Here’s how to know what size water softener to get. 

Daily Water Softening Requirement 

Adding a water softening system to your home can improve the taste of your tap water, make for more comfortable and cleansing bathing, and improve the lifespan and efficiency of your household appliances. 

The good news is that there are precise formulas for determining the water softener capacity best suited to your family’s specific needs. The bad news is that this requires gathering a lot of information and doing some math. We’ll walk you through the process to make it as painless as possible.

To size your water softener, the first thing to figure out is your daily softening requirement—or the amount of water-hardening minerals the softener will be removing each day. 

Water Hardness

To start, you need to know the hardness of the water coming into your home. There are a few different ways to determine the hardness of your local water supply. If you live in a city, you can most likely get the information through the municipal government. You can also search and find this information online—but it is not always accurate or up to date, so make sure it’s a source you can verify. 

If the water hardness data isn’t easily available, or you wish to more precisely measure the hardness of the water coming through your taps, you can purchase a home test kit. 

There are two different common metrics for water hardness. The industry standard for water softeners refers to grains per gallon (GPG), while municipal water hardness data most frequently provides the data in milligrams of dissolved calcium per liter of water (mg/L), or parts per million (ppm). To convert the measurement, divide the mg/L by 17.1 to get the GPG. 

If you live in an area with iron in the water, you need to adjust your calculation upwards, adding 3 GPG to the hardness total. 

Water hardness is rated at four different tiers: 

  • Soft: 10–50 ppm/0–3 gpg 

  • Slightly hard: 50–100 ppm/3–7 gpg 

  • Hard: 100–200 ppm/7–11 gpg 

  • Very hard: 200+ ppm/11+ gpg

Daily Water Consumption

Once you’ve determined the hardness levels, you need to compare it with your household’s daily water consumption. Your water bill should show your household’s per gallon consumption for each month. 

Ideally, you should take a look at multiple bills from a year-long period, since usage tends to vary seasonally, to find a monthly average, and then divide that by 30.5 to get your daily average. 

If you don’t have access to multiple bills, the most recent one will give you a close enough idea. If you don’t have access to recorded monthly usage at all,  you can multiply the number of people in your house by 90 gallons, the average individual consumption level in the United States.

Calculate the Daily Softening Requirement

To calculate the daily softening requirement, multiply the daily water use total by the hardness number. 

Let’s say your water hardness is 9 GPG, and your family of four uses an average 360 gallons of water per day. 360 times 9 GPG is 3240 GR—your daily softening requirement, or the number of grains the softener will need to remove each day. 

Water Softener Capacity

Holding glass and filling it with tap water
Photo: New Africa / Adobe Stock

With your daily softening requirement, you can start to compare your needs to the capacities of the water softeners on the market. 

When manufacturers describe the capacity of their softeners, they are referring to the number of grains the system can remove before it requires regeneration. Model sizes are typically marketed in terms of grain capacity (GR), with the most common options falling between 24,000 and 80,000 GR. 

Your softener should ideally be able to handle a week’s worth of household water consumption before regenerating. If the device has to regenerate too frequently, the resin will quickly wear out and need replacement. If the capacity is too large for your needs, the regeneration cycle will use more water and salt than necessary, wasting resources and money. 

The choice should be pretty simple then, right? Returning to our example above, a household with a daily softening requirement of 3,240 GR has a weekly requirement of 22,680 GR and should thus opt for a 24,000 GR system to have their softening needs met with one regeneration cycle per week. 

In practice, however, it’s not quite so straightforward. 

The grain capacity numbers listed by manufacturers are imprecise. They do not describe the number of grains removed before regeneration is required in standard usage, but rather the maximum number of hardness grains that can be removed under ideal lab conditions. 

The true capacity under real-world conditions must then be adjusted downwards a bit when making your calculations. The industry standard calculation is to shoot for 30% higher capacity than your calculation indicates is required. 

In other words, if your weekly softening requirement is 22,680 GR, you should add an additional 6,804 grains and opt for a machine that advertises no less than a 30,000 GR capacity. This puts you right in the range of the most common softener size for households with 3–4 members: 32,000 GR. 

You will get a more precise sense of the unit’s true capacity by disregarding the stated grain capacity, and looking instead at the resin quantity to understand what size water softener you need:

  • 32,000 peak grain capacity is equal to 1.0 cubic feet of resin

  • 48,000 peak grain capacity is equal to 1.5 cubic feet of resin

  • 64,000 peak grain capacity is equal to 2.0 cubic feet of resin

Consider Efficiency

For the majority of homeowners, the work ends there. If, however, you want to be absolutely certain that you’re removing the maximum number of grains at the lowest possible cost, there exist high-efficiency water softeners that include precise controls, allowing you to get more softening bang for your salt refill buck. 

Achieving the peak grain capacity touted by manufacturers requires you to use a specific amount of salt for each regeneration. For a system with 1.0 cubic feet of resin to remove 32,000 grains per cycle, for example, you may have to use 18 pounds of salt each time you regenerate it. 

With efficiency controls, you can set the same sized system to regenerate before it has reached maximum capacity. The same system that requires 18 pounds of salt to regenerate after 32,000 grains of use may only need 6 pounds of salt to regenerate after 20,000 GR—since the brine works less efficiently on totally exhausted resin beads. 

Over time, using a model on this setting will save a significant amount of money and conserve resources. 

If you’re shopping for a model touting the NSF/ANSI 44 Performance Standard, peak grain capacity or resin quantity will not be the only factors to consider in properly sizing it for your household. The packaging or the owner’s manual should also display efficiency information at three different settings in terms of grains/pounds of salt

You may very well discover that a system with 1.5 cubic feet of resin and a peak grain capacity of 48,000 can more efficiently meet your 30,000 GR requirement than the smaller model. The initial costs might be a little higher, but over time you’ll save on significantly reduced salt refills. 

How Do Water Softeners Work?

The water softener you’ll be purchasing for your home is a tank with a built-in filter composed of resin beads coated in negatively charged sodium molecules. Since calcium and magnesium ions are positively charged, the minerals are attracted to the beads and bind to the resin, causing the negatively charged sodium ions to replace them in the water that flows through your house. There are a variety of different water softener salts you can use in different systems. 

With enough usage, the resin gets depleted of sodium ions, requiring a regeneration cycle to continue softening the water. Regenerating the resin involves flushing the system with a sodium chloride—in other words, salt water—in a form highly concentrated enough to displace the ions of the hardness-causing minerals and replace them with negatively charged sodium ions.

In doing so, the system adds about 750 milligrams of sodium to each gallon of water, an amount deemed unproblematic for most by the FDA but enough to give pause to anyone trying to maintain a strict low-sodium diet. 

For those who must say “nah” to Na, there are softeners that use potassium instead, but this makes for steeper ongoing costs.

How Much Do Water Softeners Cost?

For a standard sodium ion exchange softener, expect to pay between $500 and $2,000 total for the system and installation by a water softener professional. Models that use potassium rather than sodium typically run between $800 and $4,000.

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