How do you size a salt chlorinator?
Size a salt chlorinator by how much chlorine your pool loses each day, not just by gallons. Work out the daily chlorine demand in pounds, then choose a cell whose rated output covers it within your normal pump run time, with spare capacity for hot weather and heavy use. The calculator above does both steps.
Pool volume still matters, because the same ppm loss means more pounds of chlorine in a bigger pool. If you are not sure of your gallons, start with the pool volume calculator.
How to use the salt chlorinator size calculator
- Enter your pool volume in gallons.
- Enter your daily free chlorine loss in ppm per day. Sunny, uncovered pools commonly lose 2–4 ppm a day; measuring yours is far better than guessing (see below).
- Optionally, enter your cell’s output in pounds of chlorine per 24 hours, from the spec sheet or manual.
- Read the results: chlorine needed per day, a suggested cell rating (1.5–2× your volume), and, if you entered a cell output, the hours per day it must run at 100%.
The table above shows daily chlorine needs for common pool sizes at 2, 3 and 4 ppm of loss per day.
How much chlorine does your pool need per day?
Pounds of chlorine per day = daily FC loss (ppm) × gallons × 8.34 ÷ 1,000,000. The 8.34 is the weight of a gallon of water in pounds, so this is just the ppm share of your water’s weight.
Worked example. A 20,000-gallon pool loses 3 ppm of free chlorine a day.
- 3 × 20,000 × 8.34 ÷ 1,000,000 = 0.5 lb (about 227 g) of chlorine per day
How to measure your daily loss. If you still use liquid chlorine, test FC at dusk, add nothing, and test again at dusk the next day. The difference is your daily loss. Repeat on a few typical days; sunny, busy days lose more than cloudy, quiet ones. If you already have a salt cell, turn it off for the test day and add liquid chlorine to keep FC above your minimum, then measure the same way.
How are salt cells rated?
Manufacturers rate cells two ways, and you should check both:
- Maximum pool size in gallons. For example, Hayward’s AquaRite manual lists three cell models for pools up to 15,000, 25,000, and 40,000 gallons, and notes that actual chlorine needs vary with bather load, rainfall, temperature, and cleanliness.
- Chlorine output in pounds per day at 100% output. This is the number that tells you whether a cell can keep up with your measured demand.
A pool-size rating assumes average conditions. That is why the common advice is to choose a cell rated for 1.5–2 times your actual volume. A 20,000-gallon pool would look at cells rated for 30,000–40,000 gallons. Hot climates, heavy swim use, no cover, and low stabilizer all push you toward the larger end.
How long does a salt cell need to run each day?
Hours at 100% output = daily chlorine need (lb) ÷ cell output (lb/day) × 24.
Using the 0.5 lb/day pool from the example, here is how cell output changes run time. The outputs below are example ratings, not specific models:
| Cell output at 100% | Hours needed per day | Verdict |
|---|---|---|
| 0.7 lb/day | 17.1 h | Works, but leaves little margin for hot spells |
| 1.0 lb/day | 12 h | Reasonable with a long pump schedule |
| 1.4 lb/day | 8.6 h | Comfortable; room to grow |
| 2.0 lb/day | 6 h | Plenty of reserve; can run at a lower output setting |
If the calculator shows more than 24 hours, the cell cannot keep up at that demand. Choose a larger cell, reduce demand (cover, stabilizer in range, cleaner water), or supplement with liquid chlorine.
Pump run time matters too. The cell makes chlorine only while water flows through it, and most systems have a flow switch that shuts the cell off without flow. Hayward’s manual says the filter timer should be set so all the water passes through the filter each day, and longer for high-demand pools. With a variable-speed pump, a longer run at lower speed can give the cell more hours, as long as flow stays above the cell’s minimum.
Output percentage. Most cells let you dial output down. Hayward suggests starting near 50% and adjusting based on chlorine tests every few days; it usually takes a few adjustments to find the right setting.
Why do salt pools run 60–80 ppm stabilizer?
Stabilizer (cyanuric acid, CYA) shields chlorine from sunlight. In a salt pool, the cell has to replace whatever the sun destroys, so more protection usually means less daily loss and fewer cell hours. That is why salt pools typically run 60–80 ppm CYA, compared with 30–50 ppm for pools dosed by hand.
The tradeoff is that your free chlorine target rises with CYA, roughly 11.5% of the CYA level. At 70 ppm CYA, that is about 8 ppm. A salt cell handles that well because it adds chlorine steadily rather than in one daily dose. See ideal pool water chemistry levels for every target range.
Full worked example: sizing a cell for a new salt pool
A 25,000-gallon pool in a hot, sunny climate loses about 3.5 ppm of FC a day.
- Daily need: 3.5 × 25,000 × 8.34 ÷ 1,000,000 = about 0.73 lb/day
- Suggested rating: 1.5–2 × 25,000 = a cell rated for 37,500–50,000 gallons
- Run time on a 1.4 lb/day cell: 0.73 ÷ 1.4 × 24 = about 12.5 hours at 100%, or longer at a lower setting
Before choosing, compare the run time with how long you actually want the pump to run. If your schedule is 8 hours, you need a cell that makes at least 2.2 lb/day at this demand, or a way to bring the demand down.
What affects salt cell life?
Cell life depends on how hard and how long the cell works, and on the water it works in. We do not quote hour figures here because they vary by model; check your manufacturer’s documentation and warranty. The factors you can control:
| Factor | Why it matters | What to do |
|---|---|---|
| Output setting and run hours | More total work wears the plate coating | Size up so the cell can run at a lower setting |
| Calcium scale | Scale reduces output and forces harder running | Keep the saturation index near 0; inspect the cell regularly |
| Acid cleaning | Harsh or frequent acid washing wears the plates | Clean only when scale is visible, using the manual’s method |
| Low salt | The cell works harder for the same output | Keep salt at the level in your manual |
| Cold water | Many cells cut output or stop when water is cold | Let the cell idle; use liquid chlorine if needed |
| Flow problems | Running without proper flow can damage the cell | Keep the flow switch working and filters clean |
Hayward’s manual recommends opening and inspecting the cell every three months or after cleaning the filter, and its controller reminds owners after about 500 hours of operation. That is an inspection interval, not a lifespan.
To work out how much salt to add once your cell is installed, use the pool salt calculator.
What are the most common sizing mistakes?
- Buying by gallons alone. Two pools of the same size can have very different daily demand.
- Matching the rating exactly. A cell rated for exactly your volume has no reserve for summer peaks.
- Ignoring pump hours. A cell cannot make chlorine when the pump is off.
- Low stabilizer. At 20–30 ppm CYA, a salt pool loses much more chlorine to sunlight than it needs to.
Safety note: turn off power to the chlorinator before removing or cleaning the cell, add acid to water (never water to acid) when a manual calls for acid cleaning, and wear gloves and eye protection. Electrical installation belongs with a qualified electrician. The formulas behind this calculator are listed on our methodology page.