Chemistry 101: Watson, what is Al13?

We’ve got a chemistry problem. Not you and I but the hydronics industry in general. For eons plumbing and heating contractors have been installing cast iron boilers for heating homes, commercial properties and more, all without too many problems brought about by the very material used to construct the heat exchangers of said boilers. That was then, and this is now.  

We’ve got a chemistry problem. Not you and I but the hydronics industry in general. For eons plumbing and heating contractors have been installing cast iron boilers for heating homes, commercial properties and more, all without too many problems brought about by the very material used to construct the heat exchangers of said boilers. That was then, and this is now.

To start off this detective story I have to go back a few years, back to 2005. I had only been in business and out on my own for a little more than a year and the new housing market was booming throughout Minnesota. I had started to specialize in hydronics more and more and at the time had taken on any project I could if it involved a boiler and in-floor tubing. Up until that point the only training I had received was from past journeyman while working in the new construction field.

Fast forward

All those years ago, and since, I have made mistakes here and there when designing or installing hydronic systems. Anyone who says they haven’t is either lying or has no idea the mistakes they have made. Just a couple months ago I found myself in a situation that had me playing the role of my favorite super sleuth again, only this time is was to identify and solve a problem occurring with a boiler system I had installed in my early days of entrepreneurship. This particular system had, as its heating plant, a boiler with an aluminum heat exchanger; a failed one at that but that conclusion wouldn’t come to me right away.

The game is afoot!

Error codes were popping up on the boiler control left and right over the course of a long weekend and the homeowner, a personal friend, decided that “resetting” the control would suffice rather than call me out until Monday. The code was indicating a drop in system pressure and locking out so that the boiler would not fire. This is a protection feature built in to almost all mod/con boilers and is most often encountered when there is a leak in the system. That wasn’t the only code though and resetting it would almost always get things up and running again. The next code shown upon lockout was related to temperature differential, or the rapid increase measured across the exchanger. By golly! That’s a flow problem, all I had to do there was check the primary circulator and find it wasn’t working. Problem solved! Oh, and the pressure problem? No big deal, probably related to no flow and flashing …. But the circulator was fine.

“The world is full of obvious things which nobody by any chance ever observes.” ~Sherlock Holmes

By this point, and even after reminding myself of that famous saying by the real super sleuth, I had no clues pointing me toward anything obvious. I thought I was going to have to call the local area rep for this case, and then it hit me.

Pressure and flow were definitely two problems happening, as the boiler was trying to tell me. I just had to look at it from a different perspective. While onsite I checked the condensate exiting the boiler after I got it back up and running. To my surprise I found glycol coming out of the drain tubing! The lockout code indicating the drop in pressure was due to a small crack in the aluminum heat exchanger that would only present itself as a problem when the giant block of metal was heated up, under load conditions. 

Chemistry 101

Let me put it out there right away, I’m not chemistry major. Most of the chemistry related knowledge I have has been carried with me since my junior year of high school. Most of what I remember can only be applied on a very basic level in our field of work. Add in the occasional terrible joke on the subject and I’m armed with the minimal required knowledge to remain dangerous when talking about the subject.

Back when I first installed this boiler, and I had grown fond of it at the time only to install dozens like it, there was a murmur of conversation in the industry about the use of aluminum for boiler heat exchangers. I guess at the time I was less aware of the potential problems that may arise if such a boiler was installed and not properly maintained. Well, through a crash course consisting of chemistry 101 review and on-the-job experiences with real life problems I have seen firsthand the ramifications of misunderstanding the basic principles of boiler system PH and the reaction of chemical byproducts with metals such as the aluminum used to cast this boiler’s heat exchanger.

There was a small crack in the interior of the heat exchanger, the part separating the condensate chamber and the fluid side of the exchanger. This crack would only allow system fluid through at a rate that the glycol holding reservoir was unable to overcome when the boiler was hot, or under load. When the boiler was idol the make-up system had no problem keeping up, therefor, the boiler wouldn’t lockout. This situation first presents itself as a pressure problem, and I guess it is, but the cause is due to a prolonged chemical reaction rather than a simple problem more characteristic of a run of the mill leak.

As for Al13, that’s the periodic symbol for aluminum. Aluminum, when used to construct boiler heat exchangers, has great heat storage and transfer properties. One thing to be sure of though is that you pay close attention to the manufacturer’s guidelines in respect to system fluid properties such as PH when installing or maintaining these boilers. If you’re not already familiar, you might want to brush up on your 11th grade level of chemistry too.

Eric Aune started Aune Plumbing LLC in 2004, and to carry on the tradition of family members before him, he has specialized in residential and small commercial hydronic heating systems and service. He is a graduate of Dunwoody College of Technology and Plumbers Local 15, Minneapolis Apprenticeship Training Program, and is currently a United Association Instructor and teaches for the Plumbers Local 15 JATC. Aune is also founding partner and vice president of mechanical-hub.com. Contact him at: [email protected].

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