Water softener sizing for family of 7

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Pocatello, Idaho
Hi, I have a family of 7 (2 adults and 5 kids) in Pocatello, Idaho. We are on a municipal water supply with an average of 21 gpg of hardness. I am replacing a 20 year old Culligan water softener. My local plumbing supply houses carry NuGen (https://www.consolidatedsupply.com/Product/1130711) water softeners which are using Clack valves. I am not sure which size would be best for my family. My oldest son graduates from high school this year and my daughter will graduate next year, at which point there will only be 5 of us in the house. Over the last year during non-irrigation months my average water usage per day was 359 gallons per day which seems low compared to what the "average" (75 gallons per person) is . My highest month had an average of 437 and my lowest was 338. We have 2 showers, a tub/shower and 4 toilets in the house. My plumbing is 3/4".

My questions are:
1) Should I get the 70,00 grain or the 60,000 grain water softener? Will it make much difference having the extra capacity? Will salt usage be dramatically different between the 2? There is only a $200 price difference between the 2.
2) Will a whole home filter system be worth it? I currently have an RO for drinking water. The whole home costs about $1,400. Our water is chlorinated, but it does not appear to be much. .

Any insight and help would be greatly appreciated. Thank.


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Fort Lee, NJ
Funny I'm providing advice, when I'm looking for advice. lol.
This is from a website to determine which grain level to purchase.

But even if the grain level required is lower, you have to consider the GPM speed of the water softener tank you purchase.
ie. 32000 grain tank can be 6gpm which is super slow. The guy on the phone told me I should purchase the same size tank as the carbon filter tank. Here's the formula they provided on their website. So I'm in a bit of a conundrum myself, where I only need a 32000 grain 9"x48" tank, but due to the GPM limitations, I'll buy the much larger 12"x52" tank b/c it can handle I believe 14GPM. I hope that makes sense. BUT it would be nice if a plumber can explain. lol

Sizing Your Softener:

Water hardness can be reported in "grains per gallon" (gpg), "parts per million" (ppm) or "milligrams per liter" (mg/l). Most of the industry calculates softener size using gpg. You can divide ppm and mg/l by 17.1 to obtain your hardness value in grains per gallon.

You will also need to account for the iron and manganese in your water, and a quick way to get this value is to multiply your iron and manganese concentration (in ppm or mg/l) by a factor of 4. Add this number to the hardness value you determined above. The resulting total value is similar to a "compensated" hardness value, and will better serve to size your softener.

In the example below we will use 4 people in the home and a hardness value of 10 grains per gallon, and iron concentration of 2 ppm.

Multiply 4 people in the home x 75 gallons water usage per person per day x (10 grains hardness + (2 ppm iron x 4)) = 5,400 grains of hardness to be removed per day. So with a 32,000 grain system, set capacity would be about 26,000 grains (20% lower than actual - reserve capacity), and a metered unit would regenerate approximately every 5 days (26,000 divided by 5,400), which is acceptable.

Use the formula above to adjust for the number of people actually living in your home, and your specific water hardness.

With normal to low levels of iron in your water, you can size your softener to regenerate between every 5 to 10 days. With higher levels of iron (5 mg/l and higher) and manganese (1 mg/l and higher), it's better to size a system to regenerate more frequently, in order to keep the resin bed free of accumulated deposits. In this case, a regeneration every three to five days may be required. If you have very high iron levels in your water, please contact us by email or telephone for a sizing recommendation.


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Ontario, Canada
I'm sorry I didn't see this thread when it was originally posted.

With low flow toilets and faucets, and efficient appliances now being mainstream, unless the user knows how much water is actually being consumed per month, water consumption estimates are now typically estimated as 60 gallons per person per day.

Most Water softener controllers maybe programmed for increased salt efficiency. When 100% of the resin's total capacity is depleted, the amount of salt needed will be excessive and extremely inefficient, equaling 20 lbs per cubic foot (ft3) of resin. As 1 ft3 of softening resin will typically possess 32,000 total grains of hardness reduction capacity, the maximum salt efficiency will then equal 1,600 grains per pound of salt (32,000 / 20).

Because increased salt efficiency requires a compromise in lower useable capacity and lower water quality (due to increased hardness leakage through the resin bed), the usual recommendation to achieve the best balance of efficiency, capacity and water quality, will be to base sizing estimates on using 8lbs salt to regenerate 24,000 grains capacity per ft3 of resin (=3,000 gr/lb efficiency).

Hardness settings should not be based on average hardness as stated by most municipal water suppliers. Municipal water is often obtained from multiple sources, so the hardness usually supplied to your home, maybe higher than average, resulting in the softener's capacity becoming more greatly depleted than will be regenerated each cycle. Either the hardness amount will need to be measured using a water sample obtained from your home, or the highest possible hardness will need to be programmed. Since 21gpg is the average, it's possible that hardness from one of the sources is 24 gpg or greater.

Because municipal supplies are chlorinated, any ferrous iron and manganese present at each water source, will be oxidized to a ferrous state, and will no longer consume softener capacity.

To achieve regeneration water efficiency, as there is no problematic iron or manganese present, the usual recommendation will be to size the system using efficient settings, to achieve 7+ days of capacity before regeneration is required.

Estimating 52 gallons/PP (359 gals / 7 ppl) X 7 ppl X 24 gpg (estimated hardness) = 8,736 grains daily softening load.

A softener equipped with 2 ft3 resin (=64,000 total grains capacity), will provide 48,000 grains of useable capacity when regenerated with 16 lbs of salt each cycle.

48,000 / 8,736 load = 5.5 days - 1-day reserve = an estimated regeneration frequency of 4-5 days, which is less than the 7-day recommendation.

A softener equipped with 2.5 ft3 resin (80,000 grains total), will deliver 60,000 useable grains capacity when regenerated with 20 lbs salt.

60,000 / 8,736 = 6.8 days - 1-day reserve = 5-6 day estimated regeneration frequency.

A softener equipped with 3.0 ft3 resin (96,000 grains total), will supply 72,000 useable grains when regenerated with 24 lbs salt.

72,000 / 8,736 = 8.2 days - reserve = an estimated regen frequency of 7-8 days.

With the 7-8 day regeneration frequency meeting the usual 7+ day recommendation, then a 3ft3 softener would be the usual recommended minimum size for your current water usage and estimated hardness level.
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