# Twin tank softener size calculation

smilemanOctober 27, 2010

Hi all,

I have read a lot in this forum about sizing for single tank but not very clear for twin tank. I am interested in a twin tank 9000 for a 3 bathrooms house, with washer and dishwasher, now we have 2 people but may become 4-5 in couple months. Our city report showed ~ 10gpg. I was thinking about 1.5cuft/tank, total 3cuft running at 5lbs salt dosage = 22000 gr./3500gr.(fr 5 persons x70x10) = 6.3 days x2 ~12 days in between generation. But if only 2 person this could go 22000gr./1400gr.(2x70x10) = 15.7 x2 ~ 31 days in between generation for each tank. Should I just go one tank instead? Could the experts help checking my calculation?

Thank you very much!

smileman

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justalurker

Optimum regeneration intervals would be 6-7 days on each tank of a twin the same as it would be for a single resin tank unit.

Is 5 people the imminent expected occupation of the house? Then size for 5 people. 1.5 cubes of resin @ 5 lbs of salt gets you about 19200 but that's about as low as you can go in salt dose. With 5 people you'd regenerate about every 6 days then switch to the other tank of a twin or simply regenerate a single tank unit.

If only two people will be in the house you can't short salt 1.5 cubes enough to get the #s right so you'll be wasting some water, salt, and softening capacity.

You could do it the "K" way and use a twin softener with less resin volume and regenerate more frequently but you'll give up flow rate and with 3 bathrooms you might not want to.

The question that needs to be answered is... how many people?

October 27, 2010 at 1:11PM
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smileman

Thanks justalurker for your response. Right now only 2 and my parents in law said may comes and live with us in couple months so very much still undecided. Should I buy the 1.5 cubes tank but only use 1 cube resin until more people moving in? Or do you think the single tank like 2 cubes and I short salt work better?
Thanks

October 27, 2010 at 1:56PM
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justalurker

You can't short salt 2 cubes down enough to get the numbers for 2 people to come out right. You'll most likely get channeling through the rein and that's no good.

I said "you can't short salt 1.5 cubes enough to get the #s right so you'll be wasting some water, salt, and softening capacity" so why would you think you could go up to 2 cubes and short salting would work?

If you have to pull the trigger right now then a twin with 1 cu ft in each tank is the best compromise but you'll only get a service flow rate of 9 gpm. If that will work for you then that's the best choice.

October 27, 2010 at 2:43PM
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andy_c

You wouldn't need a twin with 1.5 cuft (x2) with only 10 grain per gallon. If I recommended a Kinetico for your home I would suggest a 2030(0.8 cuft) or a 2060(1.4). A 2060(1.4) with overdrive would also do if you believe unusually high flow rates would be required (20.5 gpm @ 15psi drop). Fleck 9000 can be placed on similar sized tanks although they don't have an overdrive option. Follow Fleck's manufacturer's setting according to tank size.

The number of people is not essential like it would be with a single tank system. Twins are primarily based on water conditions whereas single tank softeners are based on both water conditions and daily capacities (grains per day).

With a twin, you never have to reset the valve for varying number of people coming and going or unusual differences in total daily volume. Sizing appropriate for water conditions will provide constant (and consistent) treated water at all times, even during regeneration.

Andy Christensen

October 27, 2010 at 4:42PM
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justalurker

Andy,

I believe I said that already... "If you have to pull the trigger right now then a twin with 1 cu ft in each tank is the best compromise but you'll only get a service flow rate of 9 gpm. If that will work for you then that's the best choice".

I understand your position that the # of people doesn't matter with a twin because the higher the water use the more frequently the softener will regenerate and that is the "K" way.

I prefer to consider the # of people and regenerate the softener in the vicinity of 6 days with a single or a twin.

We differ on whether the # of people should be a consideration with a twin but do we agree that 3 bathrooms are a consideration for flow rate?

October 27, 2010 at 5:04PM
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smileman

Thanks Andy and justalurker! Probably I will go with the 1cuft/tankx2. The only concern left is flow rate. I read something about the flow rate of Kinetico models seems higher than similar capacity Fleck system, is it true? Also, for a Kinetico system, does the price varies from one dealer to another? Where could I get a best price for a Kinetico system or I need to go through a local dealer? Thanks

October 28, 2010 at 3:58AM
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andy_c

Kinetico doesn't make a 1cuft x 2 system but 0.7 and 1.5. The smaller unit would work very well in your case.

Kinetico dealers work in territories set by the manufacturer. These can be altered by the success or failure of given dealerships. Some areas are non-exclusive which means any dealer can work with you.

Where are you from?

I don't think flow are different unless the system is an "overdrive" which means both tanks are on line at the same time. In this case, flow rate increases but other settings are adjusted to compensate. I can give you more details.

October 28, 2010 at 8:32AM
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smileman

Andy, I am from Huntington Beach, California. Could you give me more detail about the "overdrive."
Thanks

October 29, 2010 at 2:01AM
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andy_c

"Overdrive" is the Kinetico term for designing a twin-tank system whereby both tanks are on line at the same time except during regeneration. This provides high flow rate during service but cuts hardness settings. The most popular units that use OD are 2040sOD, 4040sOD, 2060sOD, 2100sOD and a few commercial models.

These are used when highere flow rates are required than a typical household.

October 29, 2010 at 7:06AM
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smileman

Thanks Andy! Do you know if my area, Huntington Beach, is exclusive or I could buy it with good price somewhere else?
justalurker, is it possible that I buy the 1.5cuft tanks and have it loaded with only 1 cuft resin then load more resin later when more people move in later and is it easy to do? (my first time so I absolutely have no idea :)).

November 1, 2010 at 1:34AM
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justalurker

Just get 1 cube in each tank.

If more people move in later the softener will regenerate more often... just like a Kinetico will.

November 1, 2010 at 1:56AM
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andy_c

smileman, I wouldn't recommend buying a softener tank(s) designed for 1.5 cubes and loading only one with the intent of adding more later. There is a little more involved in just adding resins.

With a twin, you don't need to make those adjustments once it is set for the water quality it is treating.

November 1, 2010 at 5:22AM
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asolo

Agree with andy c about the resin loading. Not that big a deal. I think you're splitting hairs a bit.

If you choose Kinetico, I doubt you'll be able to specify partial loading in any event. They do things their way and no other way.

November 1, 2010 at 2:34PM
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smileman

November 2, 2010 at 3:58AM
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