Water softener sizing

Discussion in 'Water Softener Forum, problems, installation and r' started by KMW, Dec 8, 2013.

  1. KMW

    KMW New Member

    Messages:
    6
    Location:
    MN
    I've been through a few sizing calculators and I think I know what I need for resin capacity, but I have concerns about SFR.

    My house has 3/4" copper. Family of 4, 3 full baths, 15gpg hardness, virtually no iron. No showers with multiple heads right now, but plans for one in the future. Typical usage - dishwasher, washing machine, showers daily, etc.

    Interweb seems to agree on 75 gallons per person, so that puts me at 4500 grains per day or about a 32,000 or 40,000 grain system.

    The bathtub test gives me 15gpm.

    I am considering a Fleck 7000 SXT with 1.5 cubic feet of resin (48,000) to give me enough flow. The SFR is 12gpm. Is that enough considering my bathtub test is 15gpm? How do I size it right? I've read about constant SFR vs peak. I'm guessing that peak would be around 20gpm and constant around 12gpm, but I'm really not sure how to determine that. I just sort of guessed based on what might be in use at the same time.
    Last edited: Dec 8, 2013
  2. Gary Slusser

    Gary Slusser That's all folks!

    Members of the American Water Works Association (Water COs across the US) say their customers use 60 gal/person/day. They are the ones with water meters on many millions of houses. Plus shower heads, toilets, faucets etc. are all water conservation types in most homes today. I used their figure for some 20+ yrs and checking with customers that had a control valve that measured and recorded daily water use showed 60/gals/day/person was right on. Now they didn't have anyone taking 2 showers a day or wearing clothes for a few hrs and throwing them in the laundry so it was necessary to run a couple loads of laundry a day...

    All softeners are sized by the cuft of resin, and that dictates the size of the resin tank and that dictates the control valve that can or can not be used to service the cuft volume of resin/size of the tank.

    The K of capacity is controlled by the lbs of salt used to regenerate the softener/volume of resin and the lbs are adjustable on all softeners although some companies won't tell the customer how to do it.

    In the real world, as opposed to on paper... you get a maximum of 30K of capacity per cuft of resin IF you use 15 lbs per cuft of resin. Less salt, less capacity but not the 32, 48, 64 K as many dealers and sales people claim. They are the same ones that don't help their customer size a softener or tell them anything about salt efficiency... 30,000/15lbs = 2000 grains/lb. A 1 cuft set at 6lbs gets 20K. A 1.5 at 9 lbs gets 30K and that is at 3333 grains/lb. 1333 more grains than 2000.

    Yes for SFR you add together the gpm flow of those fixtures your family normally run at the same time. A 2.0 cuft has a 13 gpm constant SFR. A 2.5' has 15 gpm. And that is real world not some inflated BS marketing type figures. And that is the flow rate of the entire softener, not just the control valve.
    Last edited: Jan 5, 2014
  3. KMW

    KMW New Member

    Messages:
    6
    Location:
    MN
    This is great, thanks Gary!

    Do you recommend SST-60?
  4. Gary Slusser

    Gary Slusser That's all folks!

    Only if you have over 5 ppm of iron (and a lot of money).
  5. KMW

    KMW New Member

    Messages:
    6
    Location:
    MN
    I'm a little confused on how I size for flow without creating a system that is too large with regards to how long it goes between regeneration. If I want to get to 15gpm SFR, that is 2.0 cuft of resin as you said. At a 6lb set, that gives me 40K of capacity, right? If I need to service 3600 grains per day, that gives me 11 days between regeneration, right? Is that too long between regenerations?
  6. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,167
    Location:
    Maine
    The 7000 SXT is a good choice for high SFR conditions and anticipating future growth. I would go with a 48k unit.
  7. KMW

    KMW New Member

    Messages:
    6
    Location:
    MN
    So 1.5 cuft resin? Will that amount of resin keep up with 15gpm SFR?
  8. Gary Slusser

    Gary Slusser That's all folks!

    KMW, I had two mistakes in my previous post about SFR.... the 2.0 gets 13 gpm, 2.5 gets 15 gpm.

    So you reduce the K of capacity to what is needed for a regeneration on average once per week as resin manufacturers suggest for residential softeners. For 3600 grains per day you do... 3600* 8 days= 28800 rounded to 29K, then 29,000/3333 salt efficiency= 8.7 rounded up to 9 lbs. Then to set gallons, 29,000/by your compensated hardness= total gallons - one day's number of gallons or grains needed per day for the reserve. Calculate that at 60 gals/person/day for all permanent residents.

    BTW, the constant SFR gpm of a softener is dictated/controlled by the cuft of resin, not the control valve as some plumbers, well drillers and water softener guys claim.
  9. KMW

    KMW New Member

    Messages:
    6
    Location:
    MN
    Thanks Gary. You lost me a bit in there, but I'm a bit slow so bear with me :)

    Basically I'm asking is do I size for K capacity needed or SFR? Based on my calculations and your help, I need about 29K system for hardness and usage alone. But if I factor in 15gpm SFR, it is more like 2.5 cuft, which should be 50K at a 6lb set. So that is much more than I need for capacity. I'm concerned that if I get the larger system it won't regenerate often enough and I'll have bacteria build up. Or I manually regenerate before it needs it, which is wasteful, right?

    So based on 3600/day needed to remove, and also hitting 15gpm SFR, how much cuft of resin do I go with?
  10. Gary Slusser

    Gary Slusser That's all folks!

    The K of capacity is adjustable by controlling the amount of refill water you program the control to allow to flow into the salt tank, that depends on whatever K of capacity you need for the regeneration schedule you want, usually on average a weekly regeneration. The SFR must be higher than the peak demand gpm your family's water use calls for.

    So... you say you need a SFR of 15 gpm, that requires a 2.5 cuft softener. Then you set the salt dose to regenerate the K of capacity you will use between regenerations, including a reserve of one day's grains or one day's gallons depending on how the control valve you have allows you to do that.

    Let's say you had a SFR need for only 9 gpm, that is covered with a 1.0 cuft, and you can cover your 29K with 15 lbs of salt and regenerate on the schedule of every 7+/- days but, you'll use a lot more salt over the amount a 1.5 cuft would use. A 1.5 cuft at 9 lbs regenerates the same 30K the 1.0 needs 15 lbs to do. That's 6 lbs less every regeneration until someone moves out or your raw water hardness decreases; that usually is years from 'now' and could be decades.
  11. KMW

    KMW New Member

    Messages:
    6
    Location:
    MN
    OK, I think I'm nearly there, thanks for the help!

    ohiopurewater.com is pushing a "Vortex" brine tank, do you have any opinions on those?
    http://www.ohiopurewater.com/shop/files/vortechspecs.pdf

    Looking at this:
    Fleck 7000 SXT
    2.5 cuft resin
    18x33 or 18x40 resin tank (do you know which size I need for 2.5 cuft? I've seen both sizes.)

    What would I set the salt dose to, 3lbs?
  12. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,836
    Location:
    Ontario California
    The Vortex is the mineral tank, not the brine tank, and most people who work in the field are less impressed by the vortex than the marketing and sales teams. There are several legitimate concerns with the design. The primary being long term service and the potential for failure. The vortex plate has seen many field related issues recently with the 12" tanks, and the benefits are "neat" but more marketing than anything else. I have yet to talk to a person who actually sets the system to use less water because it has the vortex tank. The riser is not meant to be replaced, and is it available in 32 MM or are you restricted to the smaller 1.05" riser tube? In my opinion, it is neat, but I would not use it in my rental business. I would stick to the proven and ultimately reliable gravel bed, heavy bottom screen design.

    For the 2.5 Cu. Ft. system, I would highly recommend the larger 18x40 brine tank, no salt grid needed, and I would set the salt to at least 4 pounds of salt per cu. ft., or 10 pounds of salt per regeneration.

    Also I would recommend purchasing from a company that has a business address and that assembles their own equipment and ships it themselves. Just my thoughts. :)
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