Determining the right grain capacity for your water softener is an important decision that requires considering several factors like water hardness, household size, and water usage. This article provides a detailed guide on how to calculate the ideal grains per cubic foot (gpg) for your home’s water softener.
What is grain capacity?
Grain capacity refers to the amount of water hardness minerals, measured in grains, that a water softener can remove before it needs to be regenerated. The standard measurement used is grains per cubic foot (gpg).
Hardness minerals like calcium and magnesium dissolve in water and are measured in grains per gallon (gpg). When water flows through a softener, these undesirable minerals are removed through an ion exchange process. Over time, the exchange media becomes saturated with hardness minerals and needs to be recharged to continue softening water.
The total grain capacity indicates how many hard water grains a softener can remove before it becomes exhausted. A higher grain capacity means the softener can treat more hard water before it needs to regenerate. This impacts how frequently regeneration is required.
How is grain capacity calculated?
A water softener’s total grain capacity is calculated by multiplying the system’s resin volume (in cubic feet) by the resin capacity (grains per cubic foot).
For example:
Resin volume: 1.5 cubic feet
Resin capacity: 30,000 grains per cubic foot
Grain capacity = 1.5 x 30,000 = 45,000 grains
So for this water softener, the total grain capacity is 45,000 grains before requiring regeneration.
Factors impacting ideal grain capacity
There are several important factors to consider when determining the right grain capacity for your household:
Water hardness level
Areas with harder water need a softener with a higher grain capacity, as more hardness minerals need to be removed. Hardness is measured in grains per gallon (gpg):
- 0-3 gpg = soft water
- 3-7 gpg = moderately hard water
- 7-10 gpg = hard water
- 10+ gpg = very hard water
For hard or very hard water, a capacity of at least 35,000 grains is recommended.
Household size
The number of people in your household affects water usage. More people means more water used, which translates to more hardness minerals to remove. Larger households need a higher grain capacity.
Peak water usage
Your peak water usage, during activities like showering, laundry and dish washing, also impacts grain needs. More water used means more grains to remove. Understanding your peak demand informs capacity needs.
Resin material
Standard softener resin removes around 20,000 – 30,000 grains per cubic foot. “High-efficiency” resin can remove 35,000 – 45,000 grains per cubic foot. High-efficiency resin increases capacity without needing a larger tank.
Recommended grain capacity by household size
The table below provides general recommendations for softener grain capacity based on household size and peak water usage. Use this as an initial guideline but calculate your exact needs based on your specific water hardness and usage.
| Household Size | Peak Water Usage | Grain Capacity Needed |
|---|---|---|
| 1-2 people | Low to moderate | 25,000 – 30,000 |
| 3-4 people | Moderate | 30,000 – 40,000 |
| 4-6 people | Moderate to high | 35,000 – 45,000 |
| 6+ people | High | 40,000+ |
Calculating your specific grain capacity needs
To precisely calculate the ideal grain capacity for your home, follow these steps:
- Test your water hardness – Use a test kit or ask your municipal water supplier for a report to get your hardness level in gpg.
- Estimate daily water use – Review water bills to estimate your average and peak water usage in gallons.
- Calculate peak grains to be removed – Multiply peak water use (gallons) by hardness level (gpg) to get grains that must be removed daily.
- Determine regeneration frequency – Most aim for once every 3-5 days. Budget for peak demand days.
- Calculate total capacity needed – Multiply grains to be removed daily by regeneration frequency. Add at least 10% more as a safety factor.
Using this approach provides a customized grain capacity target for your home. Also consider possible changes like adding family members or increased usage.
Other softener sizing considerations
When purchasing a new system, also factor in:
- People – Allow for at least 75 gallons per person daily for sizing.
- Water pressure – Ensure the softener you select is rated for your water pressure.
- Peak flow rate – Choose a softener that can adequately handle peak household flow rates.
- Water pH – Very acidic water requires special resin. Test your water’s pH before selecting a softener.
A professional can help select the right softener taking all these factors into account.
Special cases
In some situations, you may need to adjust the grain capacity guidelines:
- Very hard water – With levels over 25 gpg, increase capacity by 50%.
- Water with iron – Iron requires 2-3 times more capacity. Oxidizing filters can pretreat iron.
- Tannins in water – Tannins foul resin faster, needing more frequent regeneration. Use resin cleaners.
- Keep existing softener – With an existing unit, test its output to see if it meets capacity needs or install newer resin media.
Checking your softener’s capacity
Once your water softener is installed, check that it is performing adequately and meets your household needs. Here are some ways to test your softener’s grain capacity:
- Install a hardness test kit after the softener to verify the water is softened.
- Calculate the total water used between regenerations and compare to the rated capacity.
- Measure the total hardness removed by testing the drain water after a backwash cycle.
- Check that you have soft water even during peak demand periods.
If tests show your softener consistently reaches capacity too quickly, a resin cleaner may help. But you may need to upgrade to a higher capacity model.
Conclusion
Choosing the right grain capacity helps ensure your softener provides an uninterrupted supply of softened water. Consider factors like hardness level, household size, and peak usage when sizing your system. For whole home softeners, a minimum of 30,000 grains is recommended but larger households and harder water may need 50,000 grains or more. Perform tests after installation to confirm your softener’s grain capacity meets your household water softening needs.
