Are Salt Generators more economical than bleach over the lifetime of the pool?

[chem geek]

First, see this recent thread for a relevant discussion on this.

[EDIT] I have corrected an error I made below that waterbear pointed out in a later post -- I was off by a factor of 2 in chlorinating liquid quantity and therefore total cost. [END-EDIT]

Then, do the math. I don't know how much chlorine your pool uses, but let's say it's on the low side of a pool exposed to the sun of 2 ppm FC per day. Let's also assume you have a small-ish pool of only 10,000 gallons. That would require about 20.5 ounces of 12.5% chlorinating liquid per day or around 4.8 gallons per month. It costs me $3.50/gallon so that's $16.80 per month (for 10,000 gallons and 2 ppm FC per day). A similar anlaysis using bleach would lead to a roughly similar number. If you have a larger pool or use more chlorine per day, then the cost would be correspondingly higher. The 4.8 gallons corresponds to 8.33*0.125*4.8 = 5.0 pounds of chlorine per month.

Some salt cells say they can produce up to 1.5 pounds per day at around 150 Watts of power so that's 24*0.15 = 3.6 killowatts to produce 1.5 pounds or 12 killowatts to produce the 2.5 pounds of chlorine you need per month. Electricity rates vary, but even at 30 cents per killowatt, the SWG will only cost about $3.60 per month to operate (for 10,000 gallons and 2 ppm FC per day) so is much, much cheaper at generating chlorine than buying from the store.

An SWG costs roughly $1000 and the cells last, well, some say 3 years while others say 5 years -- it probably is getting better over time so let's just say it's 5 years and a new cell replacement is several hundred dollars. If we ammortize the initial cost over 5 years, that's about $200 per year. If the swim season is 6 months out of the year, then that's $33 per month. The ongoing cell replacement amortization will be about a third of that or around $10 per month, again assuming it lasts 5 years.

So, initially the salt cell is more expensive upon initial installation. As for ongoing costs, even in a reasonable best case of 5 year salt cell life, it is probably somewhat comparable to buying chlorinating liquid or bleach (ignoring initial installation and just counting chlorine generation and cell replacement). With a shorter cell life, the SWG would be more expensive. If your pool is much larger and/or used a lot more chlorine per day, then the SWG can become more economical, ignoring the inital installation cost (if you amortize that, then you are losing money during the first 5 years of use and it takes years to recover that except for the largest pools or very high FC usage).

So generally speaking, you buy an SWG for the convenience, not for the economy. However, after the initial installation, the ongoing cost (including amortized cell replacement) isn't horrible, but it depends on your specific situation.

Richard