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A Little More on pH


Feature Story


by George Lanthier


A lot of you asked me for more information on pH and how it pertains to heating systems, so here we go. If you look up pH in an encyclopedia you will find that it is ‘a measurement of the acidic level and the base of a solution in regards to the activity of hydrogen in the substance or liquid tested.”

In water-based systems, a neutral solution has a pH of approximately seven. Water-based solutions with pH values lower than seven are considered acidic, while pH values higher than seven are considered basic or alkaline. pH is generally considered to stand for ‘hydrogen power,” ‘power of hydrogen,” or ‘potential of hydrogen” and all of these terms are technically correct.

To review my previous article, a few other important things to remember when you are using anti-freeze or any boiler or system additive is to make sure that the heater, tank or heat exchanger in use is compatible with those additives. Piping materials; copper, brass, steel, etc. should also be checked for compatibility with the solution to be used and the possibility of electrolysis due to dissimilar materials. Compatibility with certain plastics should also be checked when using plastic piping variations. Make sure that the anti-freeze is an inhibited propylene glycol solution. Make sure that the antifreeze used is specifically made for hydronic heating systems and contains inhibitors for the heating system. Many of today’s glycols may be compatible with conventional systems and may not be compatible for use in radiant systems due to the radiant piping material used, always check first.

Never use glycols that were designed for automotive engines, ethylene glycol, they are toxic and if cross-contamination occurs you could make someone sick or even kill them. Many of today’s propylene glycols are specifically made for hydronic systems and are produced differently for the metals seen in boilers, pumps and other system components than for use in the automotive industry. You may even have to use a different propylene glycol because your boiler is constructed of aluminum or some other material, be careful.

Always check the pH value of the concentration after any system additive installation or during periodic maintenance. On systems containing just water or water-glycol solutions check the incoming water supply pH first to determine your baseline for the water’s pH. Then if the pH is different than seven and is not neutral, drain and flush the system and replace the water or antifreeze solution.

Most boiler manufacturers like to see the pH in their boilers, whether hot water or steam, no lower than seven and no higher than eleven, preferring a slightly alkaline solution to an acidic one, see Figure 2. The basic problem is that as the piping, fittings, boiler and everything else ages the system will actually start to turn the water, additives, and propylene glycol and water solutions to acid. So it’s important that you not only check the pH levels of the solution after an installation, but also on a routine basis.

Heating systems that contain propylene glycol should be checked at least once a year to ensure the system pH levels have not dropped below recommended levels. Most glycols are acidic in general to begin with, but through the use of the inhibitors added by the manufacturer are brought back to a more neutral state to help protect the system components. As the system ages, the inhibitors break down, causing the system pH to drop and allow the propylene glycol to return to its acidic state. At this point more inhibitors may be added if allowed by the glycol producer, but all systems reach a point where they will require a complete flush and re-fill. In some systems this could be as little as two years and for many could take as long as five to seven years, but it all depends on the water and the glycol used.

Steam boilers can be troublesome after they are installed due to oily materials and foreign agents in the boiler water like cutting oils and pipe dope. As boilers are constructed and piped, oil based cutting oils are used and can cause surging and priming of the boiler water. These oils can be found in solution on top of the water and will have a different pH than the incoming water. One method to remove these oils is to skim the boiler while maintaining a warm boiler water temperature without steaming. Another method used to clean steam boilers is through the use of trisodium phosphate (TSP). TSP is available at most hardware stores in white powder form or liquid form and is a cleaning agent and degreaser, commonly used to prepare household surfaces for painting. It is a highly water-soluble ionic salt and dissolved in water has an alkaline pH. Since TSP can corrode metal, after TSP has been used to clean the boiler it should be flushed out and the boiler refilled with clean water. With especially contaminated boilers more than one treatment of TSP may be required, so don’t forget to always flush and check pH last. TSP is also used in various forms as a boiler treatment chemical for calcium precipitation.


If copper is used above the water line on steam, the pipes and solder joints can leach into the water and make the water acidic which will not only damage the boiler, but may also not allow the boiler water to boil as easily. This is only one of the reasons for not doing above the water line steam piping in copper.

Many old timers will tell you that you must add vinegar to all new steam boilers or expect problems. Many will counter by saying that baking soda should be added; the question is who’s right? Well, they both may be, but the place to start is by flushing and draining and re-flushing a new boiler with clean water and then measuring the incoming water pH to begin with. Those that add baking soda are those that are trying to lower the acidic level of the entering water. Those that are adding vinegar are trying to reduce high alkalinity and bring the water more towards the neutral side, Figure 1, but it all starts and finishes with knowing more about the pH values you’re dealing with from start to finish.

By the way, if you are looking for a really good book on steam troubleshooting from a technician’s perspective, get a copy of Pat Linhardt’s book Linhardt’s Field Guide to Steam Heating. I’m not only using it for reference, but I’m also teaching technicians with it. You can find it in the ‘Book Store’ on my website.

So, if you work around water, and most of us do, you should have a pH tester because it will not only help you with boiler water condition problems, but can also help you with a lot of domestic hot water problems, but that’s the subject of another article.

Finally, we received a lot of phone calls, letters and emails about our article on determining the strength and quality of anti-freeze solutions. Most importantly, we got a lot of orders for our books Hydronic Systems and The Hot Water Handbook and for our refractometer and I extend to you my many thanks for your support. We also received a lot of inquiries about where to purchase a pH pen and we’re happy to announce that we have located one, Figure 2, and you can find that and everything else on our website at www.FiredragonEnt.com.

Our pH chart, Figure 1, was also very popular and yes, please feel free to use it, just don’t put it in a book or article you may be writing or we have a problem due to Copyright Laws and such.

See ya.

George Lanthier is the owner of Firedragon Enterprises, a teaching, publishing and consulting firm. He can be reached at (781) 646-2584 and his e-mail is FiredragonEnt@comcast.net.

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