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Do You Need A Check Valve Between A Salt Cell & A Heater?

pool salt cell with check valve Do you need a check valve in between a salt chlorine generator cell and your pool heater? This article aims to answer this question for you so that you can make an informed decision about your pool equipment installation. This is a technical question and one that, it seems, lacks a definitive answer...depending on who you ask of course. The main concern is that when you have a salt chlorine generator there exists the possibility that concentrated chlorine can siphon backwards through the pluming system. Chlorine injection systems are installed very last before the water is returned to the pool, and heaters are usually next to last. The area of concern is that there exists the potential for concentrated chlorine to siphon backwards through the system from the salt cell to the heater. If concentrated chlorine accumulates within the heater, even periodically, this can drastically reduce the service life of the heater. Starting with what the industry already knows to be true:

Chlorine feeders must be installed downstream from pool heaters (and all other equipment) to prevent concentrated chlorine from passing through the heater as this will damage it.

Pentair, Zodiac (Jandy) and Hayward are all in agreement with this statement. Every pool heater and salt water chlorinator that you can purchase will include information in the owners manual or installation guide that says as much. You would never install a chlorine feeder before a heater so this is a good starting point for this article. Every manufacturer agrees that chlorine buildup in heaters can, and most likely will, cause internal damage and premature failure. You would never install a feeder directly before a pool heater.

Erosion chlorinators (puck feeders) that are located downstream from a pool heater should be isolated via a positive seal, corrosion resistant check valve to prevent concentrated chlorine water from siphoning backwards through the system and accumulating in the heater.

This is another statement that all of the big name manufacturers agree with. The owners manual and installation guide for a heater from any of the big name manufacturers will include a note about the need to protect the heater from chlorine erosion feeders. Every heater manufacturer warns that a corrosion resistant check valve is required in between the feeder and the outlet of the heater. Without one the heater can be exposed to concentrated chlorine that siphons backwards through the plumbing system. A pool plumbing system is "closed loop" which can result in water moving backwards (against the force of gravity) should a pressure differential be created. An example of this would be when you open the pump lid to clean the strainer basket in your pump. Opening the lid can create a pressure differential and water can draw backwards. If you have an erosion feeder right next to a pool heater then this would mean that you might draw a big gulp of concentrated chlorine directly into your heater every time you open the pump lid.

It is important to note that all manufacturers and installation guides agree on this information. Chlorine does damage heaters in high doses, and chlorine feeders do need to be protected with check valves to stop the chlorine from them from moving backwards into the heater. This introduces the question about salt water...do salt water chlorinators also need a check valve in between the chlorinator cell and heater?

Erosion Feeders Versus Salt Water Chlorinators

The industry is in agreement that heaters need protection from concentrated levels of chlorine which can be found in erosion feeders. Equipment installation guides all make specific reference to needing a check valve in between chlorinators and heaters. What the installation guides do not mention specifically is whether salt chlorinators fall under the same level of concern as erosion feeders. Both erosion feeders and salt chlorine cells introduce chlorine into the system but can both pose a potential for damage to the heater?

Hayward - July 7, 2017 - A senior technical representative at Hayward stated over the phone that Hayward does not consider the risk from a salt chlorinator cell to be on the same level as an erosion feeder. He went on to say that Hayward does not require a check valve in between any of their brands of salt chlorinator cells and heaters and they do not consider a check valve to be required in order to meet warranty requirements.

Pentair - July 13, 2017 - Pentair technical support emailed me and confirmed that they do not consider an erosion feeder and a salt chlorinator cell the same in terms of concern for damage to the heater. They specified that they recommend a check valve in between salt cells and heaters, but do not expressly require one in order to qualify for warranty protection on their equipment.

Zodiac (Jandy) - July 7, 2017 - A Zodiac technical services representative confirmed via email that both erosion feeders as well as salt chlorinator cells fall under the area of "sanitation equipment" with them and must be protected with a positive seal check valve to prevent siphoning from allowing concentrated chlorine from accessing and damaging the heater. They did specify that a lack of a check valve would not immediately void their heater warranty. While the Hayward representative asked to not be named personally, and the Pentair representative replied to my question with only a single sentence, the Zodiac technical representative provided the most detailed response which was:

"Yes, we do consider an electronic chlorine generator to be sanitation equipment and we do require that a check valve be installed between the heater and the salt cell just the same as with an erosion feeder. To clarify the warranty impact, we don't void the entire warranty of the heater if this check valve is not installed but if it is determined that the likely cause of failure was due to a concentration of corrosive water from the salt cell then that is a reason to deny a warranty claim as we do require in our manual that a check valve be used to prevent this type of failure. But if a warranted failure occurs that has nothing to do with corrosion or no check valve we would still honor that warranty claim per our standard warranty policy."

Jeff Holmquist
Senior Product Manager - Heating & Core Equipment
Zodiac Pool Systems Inc.

two out of three pool heaters Two of the three big name manufacturers do not consider a salt chlorinator to be as significant as an erosion feeder in terms of potential for damage to heaters. Notably however one of the big name manufacturers does consider the risk from salt chlorinators enough to warrant the same level of protection that erosion feeders are afforded. Again, it is important to remember that all manufacturers agree that erosion feeders can damage pool heaters from back siphoning which means that a positive seal check valve must be used to stop that concentrated chlorine from getting to the heater.

So two out of three manufacturers are not worried about salt cells. Why is this big news? Well, first of all, I used to work for one of the big three manufacturers doing both salt chlorinator and heater technical support and warranty support. There were many cases where chlorine damage from salt cells was suspected as causing an early heater failure. Also, after over 25 years working in the industry I have noted on many occasions heaters which have failed early - far earlier than they should appear to be failing. In all of these cases a salt chlorinator cell was plumbed in downstream from the heater with no check valve in between the two. As the author of this article, and a pool and spa expert, my opinion is that chlorine from salt chlorine generators does, can, and will damage unprotected pool heaters. All manufacturers agree that erosion feeders pose a concern to heaters but only two out of three agree that salt chlorinator cells fall under the same risk category.

Erosion Feeders VS Salt Chlorinators - The real question then becomes about the amount of chlorine that is generated by a salt cell versus the amount of chlorine that can come from an erosion (chlorine puck) feeder. All manufacturers agree that too much chlorine is a problem for heaters, and erosion feeders can release enough chlorine to damage heaters. However only one of the three thinks that salt chlorinator cells pose the same level of risk. The logic is that erosion feeders can continue to dissolve chlorine and introduce it into the system while water siphons backwards. Salt chlorinators on the other hand do not continue to generate chlorine after the system flow turns off...which is good because if your salt cell kept generating chlorine under a no-flow situation then this would basically create a bomb. A literal bomb. Electronic chlorine generators produce hydrogen gas, which under a no flow situation could result in an explosion. For this reason every salt chlorinator on the market operates with a flow switch or flow sensor of some kind to stop the unit from producing chlorine once the water in the system stops flowing.

So does the flow switch inside a chlorine generation cell turn itself off fast enough to avoid developing a heavily concentrated chlorine environment such that could damage the heater? Surely we can all agree that a properly functioning salt cell and flow switch would produce less chlorine than an entire erosion feeder filled with chlorine pucks. But does this mean the potential for chlorine damage to your heater from salt water is negligible? I would argue strongly that it is not...but it would appear that my technical opinion on this matter is in the minority. Based on my personal experiences in this industry I feel very strongly that there is a direct connection between early heater failure and salt chlorinator cells on systems where the cell is not isolated with a positive seal check valve.

Protecting Your Investment

After receiving conflicting information from the big three manufacturers as to how they feel about the potential for damage to heaters from salt water chlorinators I then spoke to a number of pool companies who either service or install a large number of heaters. Much as with the suppliers, these installation and service companies were also split on their opinions about salt chlorinators, pool heaters, and the need for check valves. Many, just like myself, feel there is a strong and direct tie between early heater failure and a lack of isolating valve to protect the heater from elevated chlorine levels. Still, there were some companies who advised they do not use check valves to protect heaters from salt cells and they cite that they do not feel this is an issue for them or for their customers.

At the end of the day my feelings on this issue is that there at least exists the possibility that heaters may be damaged from the chlorine generated by salt cells. It is at least possible that the chlorine generated between the time that the system flow stops, and the time the cell ceases to generate chlorine, is enough that a non-negligible amount of chlorine can build in the system. This chlorine can then siphon backwards against gravity and enter the next component back in the system...which is the heater. Some feel that the amount of chlorine generated is not significant enough to pose a concern for damage or reduced longevity to the heater. For my money, and for the protection of my customers investment, I strongly endorse the use of a corrosion resistant check valve in between salt cells and heaters - just as required with erosion feeders and heaters. A pool heater is almost always the most expensive piece of equipment on the pool pad and if the addition of a simple valve can (even potentially) protect this heater from damage or early failure then this is a slam-dunk for me to say you should add the extra layer of protection. Why would you risk $2000 or more on a pool heater to save less than $50 on a check valve? I sure wouldn't and I suspect that given the option most pool owners would also choose to add the check valve...just in case.

Where to buy:

Corrosion resistant check valve USA

Corrosion resistant check valve Canada

Can you put chlorine pucks in your skimmer? What is pool stabilizer?

AOP systems - the future of chemical free pools

Do pools really need chlorine?

Why did my pool water turn green?

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