Why do we need to deal with water quality in a boiler? I used to ask that same question. To be honest, with the cast iron boilers I didn’t really worry about it. However, cast iron and low mass high efficiency boilers are different. The large passageways and high mass of cast iron allows a higher tolerance of poor-quality water.
Potential water problems
The two major problems water quality contributes to in a hydronic system are galvanic corrosion and scale deposits
Galvanic corrosion is defined as two dissimilar metals that are in the same conductive solution connected electrically. One metal is protected(cathode) and one is corroded(anode). This same theory is why there are anode rods in water heaters. Now that the oxygen has less metal in the system to easily attack, it starts to attack the small amounts of easily corroded metals such as cast-iron pumps and expansion tanks more aggressively. This oxidized metal is then deposited throughout the system known as hematite and magnetite known a lot of times as boiler sludge.
The difference between Hight Efficiency and Cast Iron Boilers
Both problems happen in a hydronic system if you have a cast iron boiler or a high efficiency boiler. So why do we worry about it in a high efficiency and not cast iron? Well, it has to do with tolerance.
Cast iron has large passageways so scale doesn’t drastically affect the boiler as quickly. It is there and does affect the thermal efficiency. However, because the boiler will normally have a little oversizing, it does not drastically affect its ability to heat the space.
High efficiency boilers have significantly smaller passageways and will have problems sooner. The corrosion factor is also different in a cast iron versus a high efficiency boiler. Most high efficiency boilers are made of a metal that is less likely to corrode than cast iron. That sounds good until you start to think about what is left in your system that is cast iron or steel.
You may run into water that is just fine in a high efficiency boiler without treatment. But because you can see the chemical quality of the water you will not know without testing it. Testing tools are inexpensive. If you get a PH meter, TDS (total dissolved solids) meter, and a Total Hardness test kit you will cover most of the problems that come up with water quality. All of these meters can be purchased for less than you would typically spend on a multimeter and are just as essential for those who work on boilers.
Keys to keeping the water safe
In the hydronic world there are some general rules also to keep your water in so that it will reduce the scale and corrosion.
PH levels should always be safe in the 7 to 8.5 range. Some cast iron boiler manufacturers will say as high as 10 but most want you at least above 7. Aluminum heat exchangers are very important to keep in the 7 to 8.5 range and most I have seen require it in their IOM. Stainless is best in the 7 to 8.5 range also. PH affects the ability of the water to conduct electricity. 7 is water in equilibrium of water at a molecular level. Different metals react in galvanic corrosion at different ranges. Aluminum and Stainless-Steel start to conduct at about the same range whether it is above 8.5 or below 7 they will start to react. But aluminum is lower on the galvanic scale then cast iron and steel, so manufacturers put more importance on it when using aluminum.
Grains of hardness are typically not recommended above 7 grains per gallon. Above that amount scale left behind when the water is heated starts to affect the efficiency of most boilers. They may still operate if the passages are large enough, but you will loose efficiency. Studies have shown even a 1 mm of lime can cause up to a 10 percent loss in the efficiency to conduct heat through the metal.
TDS is always recommended between 10 and 30 ppm. But TDS in drinking water regulated by the EPA will have to be below 500ppm. If you are filling from a well or a community well, your TDS may be even higher than 500. TDS is another determining factor in the ability of the water to conduct electricity. The more the dissolved solids the easier the water conducts electricity. The easier the water conducts electricity the easier the oxygen will corrode the anode metal. If the TDS is 0 and the PH is 7 you have pure water, corrosion between metals can’t happen because the ability of water to conduct electricity is theoretically 0. Now even if you remove all the non-organic dissolved solids, it will absorb some from the system piping and parts, but the amount will be much less than if it comes in with non-organic dissolved solids.
Magnet filters installed in the system are good ways to not only protect the system from small amounts of corrosion that may occur even after all your best efforts but a way to service and access the boiler water in the future. It has valves on either side of the filter so you can remove and clean the magnetic core. The item we carry at Behler-Young to perform this is made by Adey. It comes as a kit with a cleaner (MC3+) and inhibiter (MC1+) for your system or just as the filter assembly. The kit is a MagnaClean Pro 2XP Chempack or MagnaClean Pro 2XP for just the filter.
What about softened water?
You may wonder about softened water but that is not recommended by manufacturers either. The action of softening water will take care of any scaling that will happen from calcium or magnesium but it adds sodium into the system which is another element that makes water more conductive to electricity so it increases the galvanic corrosion that can occur in a system.Demineralizing water is the only solution to decrease the scaling and corroding together.
At Behler-Young we offer a solution for demineralizing through a Puropal-1. It is an item that you can either fill the system through or if you use a purge and fill valve and force your system water through. When the water runs through the Puropal-1 it will demineralize the water. It is not meant to be left in the system but as a commissioning agent. Ideal TDS readings are about 10-30 ppm when you are finished using the demineralizer. It does get spent after time and will need to be replaced but that is indicated by a color change of the beads used in the demineralizer. One other option I have seen used is pumping in distilled water. Some have even gone to the point of using an Axiom DMF150 system feeder and filling it with distilled water. This may seem extreme but when you can walk away from a system and be 100 percent sure you are not going to have a water quality call back problem it may be worth it.
Products to help the process
After demineralizing the water an inhibiter is advised to be used to reduce any amounts of corrosion that may occur because of small amounts of oxygen that may enter the systems through plastics or gaskets. Either Adey MC1+ or Sentinel X-100 could be used for that.
If you are dealing with an existing system that may have contaminants in it and you may be servicing or changing the boiler - a cleaner run through for a few days may be advisable. Either Adey MC3+, Sentinel x-400, Sentinel x-800, or RectorSeal 8-way boiler treatment may be used to achieve this. Consult their usage instructions for dosage and length of time for each product. Also always consult the boiler manufacturer to confirm the usage of cleaners and what cleaners are safe for your boiler.
Though water can be a problem for high efficiency boiler installs it can be solved. And though a high efficiency piece of equipment will operate without solving these issues it will shorten the life of items in your system whether it is a boiler, pump, expansion tank or other control. I think we can all see how the cleanest water for your hydronic system will give you the best longevity of a system. The real key is being able to convey the importance and value of the added expense to your customer.