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

[cnk]

Are Salt Generators more economical than liquid bleach over the lifetime of the pool or just easier to maintain?

[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

[CarlD]

Did I miss something in your example, Richard?

For the first 3 years, at $33/month vs $8.80 per month the SWF costs roughly 2 1/2 times what the bleach does. That means the 3 year cost of the SWG buys 8 years worth of chlorine. After that, the cost for the SWG is about 10% higher than the chlorine. So after 3 years you are 5 years behind the cost of the chlorine...and you will never catch up. But how much is the convenience worth to you? If the convenience is worth it, then it's worth it. If it's not then it's a bad deal.

Now suppose you are a super-high priced lawyer or doctor making $300/hour--If you spend an hour every month going and getting chlorine, your time cost outweighs the chlorine cost so the SWG saves more. Of course, you COULD hire someone to get you chlorine once a month--and it would not be $300 for the labor.

I suppose I could keep coming up with scenarios all night!

[waterbear]

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

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 10.2 ounces of 12.5% chlorinating liquid per day or around 2.4 gallons per month.

Richard, according to my math it would requite 20 oz of 12.5% to raise 10000 gallons 2 ppm. Did I miss something here? I also get the same results using bleachcalc. Haven't tried it in your spreadsheet. Still haven't figured the thing out! This basically doubles your cost for chlorine.

It costs me $3.50/gallon so that's $8.40 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 2.4 gallons corresponds to 8.33*0.125*2.4 = 2.5 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 6 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 $1.80 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 more typical (in-ground) pool size of around 15,000 gallons. 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.

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

You also forgot to figure in the salt and acid needed vs the acid needed with bleach. Anyway, for me the convenience factor and the lack of water problems I have seen in my own pool and my customers pools vs. manual chlorination (a large percentage of my manually chlorinating customers use liquid!) to me far outweighs any added expense, if any, from a SWG. It is interesting that the ones who say that they are not really needed or are too expensive are the ones who have never owned and lived with one! (wink, wink Carl!). I guarentee that when the day comes that they finally get one they will wonder how they did without one for all those years!
Bottom line is that I have found in my experience that pools with SWGs are more stable and have far fewer problems.

[chem geek]

Carl,

You are right that the initial installation cost will not get recovered anytime soon. I separated out that cost from the ongoing cost of chlorine generation and cell replacement. I guess that makes my analysis useful for people buying a home that already has an SWG and figuring the ongoing costs, but isn't useful for a new purchase decision where the only reason to buy an SWG would be for convenience, not for economics.

Waterbear (Evan),

Yes, I screwed up. I used 1 ounce instead of 2 when I put the number in my spreadsheet. My bad. I will correct my original post above and yes, that would double the cost for chlorine, but the SWG generating amount would need to double as well so the payback from the allocated costs is faster. I'm glad more than one person looks at this! And yes, I didn't include the mostly one-time salt and the on-going acid costs (I don't know what those are so did not include those). Thanks for catching my mistake!

Richard

[CarlD]

It is interesting that the ones who say that they are not really needed or are too expensive are the ones who have never owned and lived with one! (wink, wink Carl!). I guarentee that when the day comes that they finally get one they will wonder how they did without one for all those years!

I guess it's like getting a camera in your cell phone. You don't need but you sure love having it!

[waterbear]

I guess it's like getting a camera in your cell phone. You don't need but you sure love having it!

Carl,
The important point of my post was that pools with SWGs seem to be more stable and have fewer problems in my experience. (And we have a large customer base with varied types of pool, filter, chlorinating combinations.) Pools with SWGs and cartridge filters seem to have the fewest problems (while pools with cartridge filters on trichlor seem to have the most! No surprise here!).

[nater]

Some additional thoughts around costs for SWC:

Expenditures:
Initial salt costs: Assuming a 20,000 gallon pool needing 12 bags of salt: $55.00 ($4.57/40# bag at Lowes)

2-3 additional bags per year for dilution, splash out, etc: $15

Muriatic acid: $4.87 per gallon @ Lowes, using 6 gal/year: $30

Cost benefits:
No algecide addition
No buying/hauling/disposing of bleach bottles, splashing on clothes, eyes, skin, etc. (OK, you may need 4-6 gallons over the course of a year to cover high CL demands)
Freeze protection provided by my SWC control system (no closing chemicals, time spent closing, broken pipes, etc) Of course, this will depend on where you live
If you're a "gadget guy", then you get one more toy to play with and explain to your buddies during bbq's, swim parties, etc.

I don't think payback vs. bleach should factor into the equation to purchase a SWC system. Payback vs. being "Pool Stored" DOES factor in. But, if you're reading this, that's not a promblem for you becuase you've found this forum....