Sizing, I'm sure the forum is tired of these questions...

Discussion in 'Water Softener Forum, Questions and Answers' started by mooch91, Dec 15, 2010.

  1. mooch91

    mooch91 New Member

    Dec 1, 2010
    I've pored over water softener sizing information for the past week. For what it's worth, I'm a chemical engineer by profession and am having a little trouble making the right conclusions.

    Here are the specs:
    • Hardness - between 185 and 242 mg/L (as reported on two different tests; I used the higher value).
    • Iron - none
    • Manganese - none
    • pH - 7.3
    • Family of three (maybe 4 eventually) with high water usage (wife and I shower in AM and bathe in PM, lots of dishes and car washing); no special fixtures.
    • House with kitchen sink, scrub sink, 2 baths (1 shower, 1 tub), clothes washer, dishwasher, and three hose bibs.
    • Water is supplied by well (25 years old) - pressure between 35 and 60 psi - flow measured at bathtub around 10 gpm (if I remember correctly).

    A vendor spec'ed me a 32000 grain system but suggested I could upsize to 40000 grains. Suggested was a Fleck 2510 at 40000 grains because of the 1" internal valve (1.25 cu ft resin).

    Gary Slusser's calculator confirms about 27000 grain system but suggests a 1.5 cu ft softener size. Not sure if this is resin volume or softener size, but this would suggest a 48000 grain softener if it's resin volume (the 30K setups I've seen are 1.0 cu ft, 40K are 1.25 cu ft).

    Where I get even more lost is at the SFR calc (and I have studied Gary's page)... If my well is putting out about 10 - 12 gpm, I'm somewhere between a 1.25 and 2.0 cu ft unit per Gary's page. If I add up all my fixtures and randomly pick a plumbing code to determine SFR sizing, this has me at 2.0 cu ft+.

    Last edited: Dec 15, 2010
  2. Gary Slusser

    Gary Slusser That's all folks!

    Aug 31, 2004
    Wherever I park the motorhome.
    The K of capacity of all softeners is adjustable.

    Softeners are sized by the cu ft of resin in the tank, that cu ft dictates the size of the tank used and the salt dose in lbs dictates the K of capacity per regeneration.

    The 32, 48, 64, etc. etc. is basically inaccurate because you regenerate 1.0 cu ft to the maximum K of capacity (30K) with 15 lbs. So a 2.0 is a max of 60K @ 30 lbs. 60,000/30 = a salt efficiency of 2000 grains per lb. @ 6lbs/cuft = 12lbs you get 40K, or an efficiency of 3333 grains per lb. which is much better salt efficiency. You say you need 27K, and in a 1.0' you would need 14.5 lbs for 27K, in a 2.0 only 8 lbs. That's 6 lbs saved every 8 days or so.

    A 2.0 has a constant SFR of 13 gpm. A 1.0 has 9 gpm and a 1.5 has 12 gpm. Exceed that flow rate and the softener can not remove all the hardness.

    You should use 75 gals/person/day instead of 60.
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  4. Akpsdvan

    Akpsdvan In the Trades

    Dec 29, 2009
    Business owner/service and sales
    Some say 75 gallons per day per person.. some say 60 gallons per day per person... every person is different, I have people that use less than the 60 and some use more than 75.. it is a starting point and often with older washers, shower heads, toilets etc.... so water usage will be higher but if one is changing to newer then the number will go down.

    For years I have been using 1.5cubic units with 9lbs.. 31k along with 2-4 people and the units are still doing very well and no problems with staining or hard water past the units.

    After a unit goes in and the meter was set for say 1200 taking 300 off for buffer if the water quality is good ,, ie 0 hardness and 0 iron then maybe cutting down on the buffer by 50-100gal... as I said every family is different in water usage and there is no right or wrong in usage, just a starting point and working from there.
  5. Gary Slusser

    Gary Slusser That's all folks!

    Aug 31, 2004
    Wherever I park the motorhome.
    I think that the reason that works for you is due to the large buffer you use.

    I was taught to use a 24 hr reserve, and 60 gals/person/day. That was about 25 yrs ago. In this case since the OP and his wife shower in the morning and then have a bath in the evening, I said 75 but 75/person/day that is very rare from my experience. I say that due to the last 6.5 yrs using a control valve that recorded actual water use gallons for the last 21 days.

    BTW, since we're here.... it also recorded the highest gpm run through it daily for the last 6 days and then the highest gpm ever since the day it was installed. So far I have not heard that I got the SFR wrong, close, within a gallon or 2 but not over. Most dealers pay no attention to the peak demand of the house and thereby the constant SFR gpm size of the softeners they sell.
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