A fortnight of scale in the kettle is a reading
The kettle furs again two weeks after it was descaled. Towels come out stiff and grey rather than clean, and the detergent dose keeps creeping up to fix it. The shower screen films over the day after it was wiped and the kitchen aerator blocks with white grit every few months. None of that is dirt or a fault in the appliances: it is calcium and magnesium arriving continuously in the supply and leaving solution wherever the water is heated, evaporated or pushed alkaline by soap. The grey laundry is the same chemistry running the other way, hardness reacting with surfactant into an insoluble curd that stays in the fibres.
Those symptoms are qualitative and the machine you are about to buy is not. Everything downstream is arithmetic on one number, and hardness is reported in at least six units that are not close enough to guess between. The calculator further down works in grains per US gallon, the unit the North American softener trade sizes in. A grain per Imperial gallon — the Clark degree still printed on some British literature — is a smaller quantity for the plain reason that the gallon underneath it is larger. German and French degrees differ again, and a laboratory result may arrive as milligrams per litre of calcium rather than the calcium carbonate equivalent everyone quotes. Convert first, size second.
The number itself comes from one of three places, in descending order of trust. A laboratory analysis of a drawn sample is the good answer, and it prices in below the cost of the mistake it prevents. A municipal supplier's published figure is next: in the United States that is the annual water quality report, and in the United Kingdom it is the hardness figure the water company publishes by supply zone or postcode. A test strip at the tap is the quick answer and is fine for confirming an order of magnitude. Whichever route, take the sample from upstream of any existing treatment. A strip held under the kitchen mixer in a house that already has a softener on it measures the softener, not the supply, and that mistake has sold a great many correctly working units a replacement.
Ask for the range rather than the average where the supply is blended, because a town fed from a borehole in summer and a reservoir in winter can move several grains across the year and the equipment has to cope with the hard end. While the sample is out, add iron, manganese, pH and the disinfectant residual to the same report: those four decide whether the resin survives at all, and they cost almost nothing alongside a test already being run. By U.S. Geological Survey classification anything over 180 mg/L as calcium carbonate, about 10.5 grains per US gallon, is very hard — which is where most households asking this question sit.
| Unit | In mg/L as CaCO₃ | Where it turns up |
|---|---|---|
| 1 grain per US gallon (gpg) | 17.1 | North American softener ratings, and the calculator on this page |
| 1 Clark degree (grain per Imperial gallon) | 14.3 | Older British literature; a sixth smaller than a US grain, because the gallon under it is a fifth larger |
| 1 German degree (°dH) | 17.85 | German and Central European equipment, resin data and test kits |
| 1 French degree (°fH) | 10.0 | French and Southern European ratings, often as m³·°fH of capacity |
| 1 mg/L as calcium (Ca) | 2.5 | Laboratory reports that give the element rather than the equivalent |
| 1 mmol/L of hardness | 100.1 | Scientific reporting and most European water analyses |
What is actually in the tank
A softener filters nothing. The vessel holds beads of strong-acid cation resin loaded with sodium, and as hard water passes through the bed each calcium or magnesium ion is held back and two sodium ions are released in its place. Hardness leaves and sodium arrives, equivalent for equivalent, which makes the sodium addition calculable rather than a matter of opinion: roughly 7.9 mg/L for every grain per US gallon removed. On very hard water that is a real number, and it belongs in the conversation with anyone in the house on a sodium-restricted diet. The US Environmental Protection Agency publishes a taste-based drinking water advisory for sodium and the World Health Organization puts the taste threshold around 200 mg/L — neither is a reason to abandon the project, both are a reason to decide deliberately which taps get treated water.
The bed is finite and it fills up. When it is full it is washed backwards to lift and reclassify the beads, flooded with brine drawn from the salt tank so that concentrated sodium drives the exchange in reverse, rinsed, and put back into service. That whole cycle is regeneration, and it is the reason the machine has a second tank beside it, a drain line leaving it, and a valve on top clever enough to decide when. The valve is a meter with a decision attached: it counts the gallons it has passed, subtracts the grains those gallons carried, and starts the cycle when what remains falls below a reserve. Everything that follows in this guide is one of two questions asked of the assembly below: how many grains it holds between regenerations, and how many gallons a minute it will pass while holding them.
The column, top to bottom, and the salt tank beside it
- Control valve head — counts the water it passes and starts a regeneration when the reserve is reached, and every gallon of the house's peak flow squeezes through its ports Water Meter Sizing Calculator (Fixture Units)
- Freeboard and upper screen — empty space above the bed, sized so the resin can expand roughly half again during backwash without washing beads out to drain
- Resin bed — the exchange capacity itself, quoted in grains per cubic foot and worth less than the nameplate whenever the salt dose is set for efficiency Water Softener Sizing Calculator
- Gravel underbed and lower basket — supports the bed and spreads flow across the whole section, so the water cannot cut a channel down one side and leave hardness through
- Pressure vessel — a filament-wound composite tank on the house supply pressure, heavy enough loaded that it wants a solid level base rather than a shelf
- Brine tank and safety float — holds the salt and the saturated brine drawn for each cycle, with a float that closes the fill before the tank can overflow onto the floor
Grains for the week
Capacity sizing multiplies three things: how many people, how much water each uses in a day, and how many grains each gallon carries. That gives a daily grain load, and multiplying it by the days you want between regenerations gives the capacity the bed has to hold. The middle term is the soft one. Seventy-five gallons per person per day is the convention the North American trade sizes on, while the metered evidence in the Water Research Foundation's Residential End Uses of Water sits appreciably below it for indoor use — the planning figure survives because it quietly covers the long shower and the household doing eleven washes a week.
If the property has a meter, do better than any table. Read it a fortnight apart with the irrigation off, divide by days and occupants, and the household's real consumption replaces a national average — along with everything a per-person figure never asks about, from a leaking cistern to a second dwelling on the same supply. Write down whichever figure you used, because whoever diagnoses a complaint in three years needs to know if the sizing assumed a family of four.
Now the correction that decides whether the unit is right or merely plausible. The familiar grain ratings on the box are capacities at maximum salt dose. A cubic foot of standard resin regenerated at fifteen pounds of salt gives around thirty thousand grains, which is where the 32,000-grain badge comes from; the same cubic foot at eight pounds gives closer to twenty-two thousand. Nobody who cares about running cost regenerates at maximum dose, so working capacity sits materially below the nameplate. Read the calculator's grain figure as the requirement, then check it against what the candidate unit delivers at the salt setting you intend to run.
Worked through, that argument usually buys a bigger tank and a smaller salt bill at once. A household of four on 18 grains per US gallon burns 5,400 grains a day and needs about 37,800 between weekly regenerations. A 1.5 cubic foot bed reaches that only at around ten pounds of salt per cubic foot — fifteen pounds a cycle, bought at roughly 2,500 grains for every pound. A 2 cubic foot bed at six pounds per cubic foot delivers about 40,000 grains for twelve pounds of salt, at nearer 3,300 grains a pound: more headroom, less salt, fewer chlorides leaving the property, longer contact time. The larger vessel costs more once and saves every week after.
There is a ceiling on that logic. A heavily oversized bed sits between regenerations for a fortnight, and resin standing idle and wet in the dark is where biological fouling and channelling begin; manufacturers impose a calendar override for that reason, forcing a cycle after a week or two whether the capacity was used or not. Size for a regeneration every few days to about a week, and add capacity honestly for what the hardness figure omits — clear-water iron is compensated by adding several grains per gallon of apparent hardness for each part per million of iron, by the equipment maker's own method rather than a remembered multiplier.
This gives the grains the household burns between regenerations, which is the requirement rather than the answer — the unit you buy has to deliver that figure at the salt dose you plan to run it at, not at its nameplate dose.
Number of people in the household.
Your water hardness in grains per gallon (GPG).
How often you want the softener to regenerate.
Recommended softener capacity
24,000 grains capacity
This is a standard rule-of-thumb sizing method. Iron content, unusually high water use (irrigation, hot tubs), and manufacturer-specific efficiency ratings can shift the ideal size.
- Daily softening demand
- 2,250 grains/day
- Capacity needed before rounding
- 15,750 grains
They open the calculator with your figures already in it
Water Softener Sizing Calculator: 24,000 grains capacity — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 24,000 grains capacity — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- The size it recommends is a nameplate grain rating, and nameplate ratings are measured at maximum salt dose. Run at the lower, more economical salt settings most units are actually set to, the same bed delivers materially fewer grains per cycle. The figure also holds back no reserve, while a metered valve starts a cycle before the bed is exhausted, so real intervals come out shorter than the days you picked.
- Water use is a flat 75 gallons (284 litres) per person per day, a planning convention rather than your household's measured consumption. Irrigation, a pool or hot tub top-up, a home business, or a second dwelling on the same supply are not in that figure. Two meter reads a fortnight apart with the irrigation off beat it.
- Only calcium and magnesium hardness is counted. Iron and manganese consume exchange capacity too and have to be added to the hardness figure by the equipment maker's own method; sediment, chlorine and extreme pH foul the bed or shorten resin life without changing this number at all.
- This is the grains side of the job only. It says nothing about the control valve's service flow rating, the pressure drop that costs when three fixtures run together, or the resin bed's own service flow limit — a tank with enough grains still passes hardness if water is pushed through it too fast. The sizes it chooses from are common single-tank residential ratings; twin-tank and commercial units are outside it.
- This is not a compliance check. Brine discharge to a septic system or sewer is restricted or banned in some jurisdictions, the drain line carries its own air gap and sizing requirements, and softening adds sodium to the treated water in proportion to the hardness removed — none of that is in this calculation.
Gallons for the minute
Capacity is a week's problem. Flow is a thirty-second one, and it is what the household will actually complain about. The moment that matters is the ordinary evening collision: someone in the shower, someone rinsing at the basin, and the washing machine taking its fill. In a house there is no diversity to hide behind, because a household of four is not a statistical population — those three outlets genuinely do run together, most days, at a predictable hour. Add their rated flows and you have the honest peak: a showerhead held to 2.5 gallons a minute under the US Energy Policy Act, or 2.0 if it carries the WaterSense label, a lavatory tap at 2.2, and a washing machine drawing whatever its inlet valve passes for a couple of minutes. That is comfortably into single-figure gallons per minute, and every one of them has to pass through the valve on top of the tank.
The fixture-unit route reaches the same question from the other direction and is worth running as a cross-check, since it is how the rest of the supply was sized. Treat its answer as an upper bound rather than a design flow for a single dwelling: the curve descends from Roy Hunter's 1940 work at the National Bureau of Standards, whose fixtures drew far more water than modern ones, and its over-prediction at the small end is precisely why IAPMO's Water Demand Calculator exists as an appendix to the Uniform Plumbing Code. On a house the additive check is closer to what the valve will see, and the fixture-unit figure says how wrong the sizing can afford to be.
What the flow figure buys is a reading of the manufacturer's flow table, and there is one honest way to read it: a service flow rating means nothing without the pressure drop it was measured at. Residential valves are quoted at a peak flow against a stated drop, commonly fifteen pounds per square inch, and again at a lower continuous rating; those are two different promises. Fifteen psi is a serious deduction from a supply already marginal at the top of the house, and it is spent before the pipework and the height of the bathroom have taken their share. Where entry pressure is comfortable this is a non-event; where it is not, the valve size rather than the tank size is what has to change, because a one-inch and a three-quarter-inch valve on the same vessel are different machines.
The bed has its own opinion about flow, separate from the valve's. Exchange needs contact time, so resin data sheets publish a service flow range per cubic foot along with a peak that must not be sustained. Push water through faster and hardness appears at the taps while the bed still holds capacity — which reads on site as a failed softener and is in fact one asked to work too quickly. The same sheets set a backwash rate per square foot of bed area, and that rate falls as the water gets colder, because cold water is more viscous and lifts the bed further at the same flow. A unit in an unheated garage backwashes differently in January than the August commissioning sheet suggests.
Run the fixture-unit total for everything downstream of the softener to bound the peak demand from above, then compare it with the three fixtures you know run together — on a single dwelling the two will not agree, and the disagreement is the margin.
The sum of water supply fixture unit values for every fixture served by this meter.
A calibration constant that scales the square-root approximation to your building's fixture mix.
Estimated peak demand
22.6 GPM
A meter is sized on peak demand and on the pressure it costs you, not on the size of the pipe it sits in. Fitting a meter one size up because the main is large is a common and expensive error — an oversized meter under-registers low flows.
They open the calculator with your figures already in it
Water Meter Sizing Calculator (Fixture Units): 22.63 GPM — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 22.6 GPM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Does not compute the meter's pressure loss at the design flow, which must be subtracted from the available pressure before sizing the distribution.
- Excludes fire demand entirely. Where a supply serves both domestic use and a fire system, the sizing basis and often the meter type are different.
- Meter accuracy classes have a minimum registrable flow. Continuous small leaks below that threshold pass unmetered, which matters for leak detection rather than for billing.
The bore, the yoke and the bypass
The pipe into the softener and the pipe out of it are sized on the same terms as the rest of the supply: the flow they carry, the friction it costs, and a velocity ceiling that exists so the pipe neither erodes itself nor sings at three in the morning. Two habits around the machine cause trouble. One is fitting a one-inch valve on three-quarter-inch pipe and expecting the valve's rated flow the pipe was never going to deliver; the other is running an inch of copper up to three-quarter-inch ports and assuming the bore protects you from the restriction. The narrowest thing in the path governs, and on most installations that is the valve.
Position matters as much as bore. Keep the unit near where the supply enters the building, near a drain it can discharge into, and clear of a floor that floods. The bypass is not optional — the integral one on the valve or a three-valve arrangement in the pipework — so the house keeps its water while the softener is isolated for service. Every softener eventually needs isolating, and the ones without a bypass get isolated with a hacksaw. Set the vessel on something level and solid, use unions at the yoke so it comes out without cutting pipe, and keep a soldering flame away from a plastic valve body: make the joints on the bench and bring them cold.
Size the run to and from the softener on the load it carries and the velocity the material tolerates, then compare that bore with the valve's port size — the smaller of the two is the one the household will feel.
The sum of water supply fixture unit values for every fixture served by this pipe segment.
A calibration constant that scales the square-root approximation to your building's fixture mix.
The maximum velocity allowed in the pipe to limit noise and water hammer risk.
The pressure available where the supply enters the building.
The length of pipe from the point of supply to the furthest fixture, following the run.
How much extra length is added to represent the elbows, tees and valves in the run.
The height of the highest fixture above the point of supply.
The pressure the metering assembly loses at your design flow.
The flow pressure the furthest fixture needs at its inlet to work properly.
Which Hazen-Williams roughness coefficient the friction calculation uses.
Minimum pipe diameter
0.862 in
Velocity governs this run. The diversified demand would fit through a smaller bore on pressure alone, but sustained velocity above the ceiling erodes the pipe and is audible through the building, so the velocity limit is the binding one and the pressure budget has room to spare.
- Estimated peak demand
- 14.31 GPM
- Diameter set by the velocity ceiling
- 0.86 in
- Diameter set by the pressure budget
- 0.77 in
- Pressure lost to static lift
- 58,286.8 Pa
- Pressure lost to friction at this diameter
- 122,120.36 Pa
- Pressure left at the furthest fixture
- 198,803.83 Pa
- Equivalent length used for friction
- 147 ft
They open the calculator with your figures already in it
Domestic Water Pipe Sizing by Fixture Unit Calculator: 0.8616 in — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 0.862 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Fixture-unit methods work because fixtures are used intermittently and rarely together. That diversity is the whole basis of the sizing, and it is why the pipe is far smaller than the sum of the fixture flows would suggest.
- Hunter's curve is old, and its age biases this in one direction. It was derived in the 1940s from fixtures using several times the water modern ones do, and it is well documented as oversizing systems built with low-flow fittings — the demand factor is the handle for that, and lowering it is a judgement with consequences rather than a correction.
- Excludes continuous-demand loads such as irrigation and hose bibs, which do not benefit from diversity and are added at their full flow.
- The friction calculation assumes one diameter for the whole run. A real system steps down as branches leave it, so the true loss is somewhere between this figure and the loss of a system sized entirely at the smallest branch — this is the screening answer, and a segment-by-segment calculation is the design one.
- Fitting losses are an allowance, not a count. Each elbow, tee and valve has its own equivalent length and a push-fit insert reduces the bore as well, so the percentage is a stand-in for a takeoff nobody has done. On a run with many tight bends it will understate the loss.
- The meter figure is yours to supply and this page cannot check it. Meter loss rises steeply as flow approaches the meter's rating and a backflow preventer or pressure-reducing valve often costs more than the meter itself; entering a nominal figure where the real assembly loses far more is the quiet way this calculation goes wrong.
- Velocity limits govern independently of flow: sustained velocities above roughly 2.4 m/s (8 ft/s) cause erosion and noise regardless of what the fixture units allow.
- The result is an internal diameter, not a pipe size. Nominal designations are not bores — copper, PEX and CPVC of the same nominal size have materially different internal diameters, and a push-fit system loses more at every joint — so take the next size up whose actual bore meets this figure in the material you are using.
What gets soft water, and what must not
Softening the whole supply is the lazy default and it is wrong in at least three places. Outside taps and irrigation take hard water: plants do not want the sodium, the lawn does not care about scale, and every grain spent on the garden is regenerated with salt. Branch those off upstream rather than relying on somebody remembering a bypass lever in June. The drinking-water tap deserves the same thought in the other direction, since the sodium added is proportional to the hardness removed — a hard branch to the kitchen cold tap or a reverse-osmosis tap beside it, decided with whoever in the house has reason to care.
The one missed on newer houses is fire protection. Where a dwelling has a sprinkler system under NFPA 13D, that supply is not a domestic branch and does not pass through treatment equipment: a fouled bed or a valve stuck in regeneration is a restriction in a life-safety supply. Take the connection ahead of everything and label it so a later reconfiguration of the plant space does not undo it. The water heater is the same argument inverted — it goes downstream, because a heat exchanger is where hardness precipitates first and hardest, and it is the appliance the whole project is really protecting; Battelle Memorial Institute's testing for the Water Quality Research Foundation is the usual citation for how fast that costs money.
The regeneration discharge is a drain problem, and the codes treat it as an indirect waste rather than a connection. It terminates over a receptor with an air gap: a standpipe, a laundry tub, a floor drain with the required separation. Hard-piping a softener drain into a waste line makes a cross connection between a potable appliance and the drainage system, and it is the commonest code failure on domestic installations. The brine tank overflow needs its own indirect termination and is not a spare hole to tee the drain into. Check the manual for the drain line's permitted length and lift, because backpressure there changes both the backwash rate and the brine draw.
Electrical bonding is last on the list and the thing nobody photographs. Cutting a metallic cold main to insert a softener with a composite valve body breaks the continuity of a pipe system the electrical installation may be relying on. NFPA 70, the National Electrical Code, requires metal water piping to be bonded and that path to stay continuous around removable equipment; BS 7671 imposes main protective bonding on an incoming metallic service for the same reason. A jumper across the softener is cheap and not negotiable, and it is the electrician's call rather than the plumber's guess.
Order the rest of the plant by what each stage needs from the one before it. Sediment and iron treatment go ahead of the softener so the bed is not asked to do a filter's job, and on a well the pressure tank and pump control stay upstream of all of it. On a municipal supply the equivalent question is the disinfectant residual: free chlorine attacks the crosslinks in the resin and chloramine does the same more slowly and more relentlessly, which is what a carbon prefilter is defending against — and it becomes a maintenance item of its own.
- Confirm the entry point pressure and the pipe material before anything is ordered, and note where the existing supply is already restricted.
- Branch the outside taps, the irrigation and any NFPA 13D sprinkler supply off upstream of the softener position.
- Set the vessel and the brine tank on a level solid base, within the manual's stated distance of both a drain receptor and a socket.
- Make up the yoke with unions and isolating valves so the unit lifts out without cutting pipe, soldering nothing at the valve body.
- Run the drain to an air gap over the receptor within the manual's length and lift limits, and terminate the brine overflow separately.
- Fit the bonding jumper across the interruption in the metallic pipe run, or have the electrician confirm none is needed, then fill the vessel slowly to purge air before putting the bed into service.
Salt is the running cost, and the drain is the other half
Every cycle spends salt and water, and the amount is a setting rather than a fact. The relationship is unhelpfully shaped: the first few pounds per cubic foot buy a lot of capacity and the last few buy very little, which is the whole efficiency argument and the reason a large bed on a modest dose beats a small one flogged at maximum salt. NSF/ANSI 44 rates residential softeners on exactly this basis, in grains exchanged per pound of salt, and no unit can claim the efficiency rating while regenerating on a fixed clock. Take the certified figure from the model's listing rather than the brochure, and check there that the wetted materials are covered by NSF/ANSI/CAN 61 and 372.
Potassium chloride is the alternative regenerant where sodium is the objection, and its penalty is arithmetic rather than performance: its equivalent weight is higher, so about a quarter more by weight does the same exchange. Grade matters whichever salt is used — clean pellet or solar salt leaves little behind, while the cheapest rock salt silts the bottom of the brine tank until the draw blocks. Keep the tank no more than about two thirds full, because a deep column of salt in a damp tank is what bridges: a hard crust spanning the walls with a void beneath it, so the machine draws brine from empty space and delivers hard water while the tank still looks full.
The water side of a regeneration is tens of gallons, and where that water goes is a local question with real teeth. The volume lands on the bill, on a well's recovery, and on a septic system's hydraulic load; the chlorides in it land on whatever treats the wastewater. Some jurisdictions restrict or prohibit self-regenerating softeners for exactly that reason — California's Assembly Bill 1366 gave local agencies that power in response to chloride limits on discharges. Check the rule before the equipment arrives, not after the inspector does, and where discharge to a septic system is permitted, size the field on the load including it rather than beside it.
Timing is the last setting and the easiest to leave wrong. Valves default to the small hours because a cycle takes water and puts the house into bypass on hard water while it runs — right for most households, wrong for anyone working nights, and a two-minute change at commissioning rather than a fault to diagnose later.
| Salt dose per cubic foot of resin | Capacity per cubic foot | Grains exchanged per pound of salt |
|---|---|---|
| 6 lb (2.7 kg per 28 L) | about 20,000 grains | about 3,300 |
| 8 lb (3.6 kg per 28 L) | about 22,500 grains | about 2,800 |
| 10 lb (4.5 kg per 28 L) | about 25,000 grains | about 2,500 |
| 15 lb (6.8 kg per 28 L) | about 30,000 grains | about 2,000 |
Proving it on the day, and the year after
Commissioning a softener is not watching it fill. Force a manual regeneration and stand with it: the backwash should run visibly to drain without carrying beads out, the brine draw should pull the salt tank level down measurably, and the refill should stop where the float says. A cycle that never draws brine is the commonest silent failure there is, because the machine keeps counting and keeps delivering hard water while every indicator on the front says it is fine. Then test a treated tap, and the hard branch too, to confirm the pipework does what the drawing says.
Aim for a small residual rather than zero. Most installers set a blend that leaves a grain or two, partly because completely soft water feels slippery to people who are not expecting it, and partly because removing all the hardness also removes the scale film that was quietly lining the pipework. Softening adds nothing corrosive on its own, but on a supply that was already aggressive — low pH, low alkalinity — losing that film can show up as blue-green staining at the fittings. Where there is lead pipework or lead solder in the house, that is not a change to make casually; the water supplier will say what it doses for plumbosolvency control and that answer belongs in the decision.
Later failures have signatures worth knowing. Hardness creeping back while salt use stays normal means the bed has lost capacity — to oxidation by the disinfectant residual, or to iron fouling a resin cleaner may or may not recover. Good water with salt use climbing means brine is being made and wasted, which points at a valve cycling too often or a leaking seal. A drain line running continuously is a valve stuck in cycle, expensive in a way that takes a quarter to appear on a bill. And re-test the supply every few years: if it has changed source, the settings from three years ago are sizing for water that no longer arrives.
- Force a full manual regeneration and watch each stage, confirming the brine level falls during the draw.
- Test hardness at a treated tap and at the hard branch once the cycle has finished and the bed is back in service.
- Set the blend to leave a small residual rather than zero, and record the setting on the vessel.
- Check the drain keeps its air gap and does not splash out of the receptor at full backwash flow, then operate the bypass and confirm the house keeps supply with the unit isolated.
- Write the hardness figure, the assumed occupancy, the salt dose and the regeneration day inside the salt tank lid for whoever comes next.
What to have in hand before ordering
None of this can be read off the appliance brochure, and every figure has a source outside the plant room. The link opens the sizing already loaded with a household of four on very hard water, ready to be replaced with the property's own numbers.
- Supply hardness, in the unit it was reported — From a laboratory result or the supplier's published figure for the zone, converted to grains per US gallon before it reaches any sizing method.
- Iron, manganese, pH and disinfectant residual — The four results that decide whether the resin survives; clear-water iron is compensated into the hardness figure and oxidised iron is filtered out ahead of the bed.
- Metered daily use, not a per-person table — Two weeks of meter readings divided by days and occupants beats every planning figure, and it exposes the irrigation nobody mentioned.
- The three outlets that realistically run together — Each at its rated flow, summed — this is the peak the control valve has to pass, and it is a different number from the fixture-unit estimate.
- Pressure at the entry point at the worst hour — What the supply guarantees at the boundary, less what the run to the softener has already spent, sets how much drop the valve may be allowed.
- Drain receptor, air gap, and the lift to it — Where the regeneration discharge goes, how far and how high the line runs against the manual's limits, and whether local rules permit it to reach a septic system.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.