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Dirty hydronic systems are nothing new. Every person I’ve spoken to in this trade can tell you horror stories ranging from plugged piping to failed boiler heat exchangers. It’s a scenario that nobody wants to be part of, whether you’re a homeowner paying the hefty bill or a contractor pulling their hair out.
What I find so interesting is that of all the stories I’ve heard, very few speak of the actual problem. On the surface, the problem and solution seem simple. You’ve got dirt and debris, and you have to get it out. Let’s take a step back and figure out how exactly the dirt got there in the first place.
Installing these systems can be a dirty business; that’s usually where most of your debris will come from initially. Copper shavings, thread tape, weld slag, solder and even flux are all things you’ll find. You can even have literal dirt in your system if you’re lucky enough to be fusing pipe in a ditch for a geothermal loop field.
We should all be doing our best to prevent these things from getting into our systems, but it happens despite our best efforts. Where most trip up is with older systems; the origins aren’t as clear as the problem can’t always be blamed on the poor, scapegoat installers.
Diagnosing older systems
Many of the existing, aging systems plagued with debris usually suffer from problems due to oxygen combined with ferrous components or piping. This oxygen starts the corrosion process and can break down those components. This happens every time you fill a system.
However, once the excess oxygen is used up in the corrosion process, the corrosion stops. It is why we can use cast-iron and steel components in closed-loop hydronic systems. That should be the end of the story, but if there happens to be a continued source of oxygen, corrosion marches on.
If you are experiencing an oxygen problem, it’s my experience that you’ll see the first signs at your diaphragm-style expansion tanks and panel radiators. These items are in a scenario where thin steel is in direct contact with the system fluid. Under normal circumstances, this is not a problem. However, if your fluid is full of oxygen that’s constantly being replenished, then that steel is under constant attack.
So, if you’re regularly replacing pin-holed expansion tanks on systems, it’s time to start digging for the problem instead of blaming it on inferior components.
Usually, there are a few good places to look for continued oxygen ingress into your systems. The first is at the air vents. But wait, don’t air vents let air out of a system? That’s very true, but they’re also good at letting air in.
You need to make sure your fill pressure is high enough to maintain a positive pressure at the air vents and throughout the system during any point in operation. If there happens to be a negative pressure, you can bet that air vent will bring air (and oxygen) right back in.
The second place to look is your piping. Does your PEX piping include an oxygen barrier? Did someone install potable PEX piping in the system? Without the oxygen barrier (and with, to a much smaller extent), oxygen can continually diffuse through the pipe, allowing corrosion to continue in any ferrous components.
If that’s the case, it’s usually a good idea to eliminate any ferrous components from the system. This may mean separating your boiler from the rest of the system through the use of another heat exchanger.
An honorable mention goes out to leaking systems. If your system is leaking, it usually means it’s also bringing in fresh water, and oxygen along with it, to maintain system pressure. This oxygen will ensure continued corrosion.
Chances are, the leak is in a slab or elsewhere hidden from plain view. This is where I would recommend installing a water meter on the boiler fill line to keep track of consumption. It’s also a good time to buy a new toy like an infrared camera to check for big, hot blobs in your concrete.
No matter where the dirt comes from, all hydronic systems deserve a device dedicated to the capture and removal of debris. Without the use of one of these devices, the responsibility will usually fall on the most expensive and difficult-to-service components such as heat exchangers, circulators and balancing valves.
It’s important to make sure that the device you’re using is capable of removing ferrous debris as well as nonferrous debris. Ferrous debris, also referred to as magnetite, will wreak havoc on variable-speed, wet-rotor circulators and heat exchangers with little regard to how much they cost. These particles are very small, down to 5 microns, which means that an average strainer basket isn’t going to get the job done. You’ll need something a bit more specialized.
When using any dirt-catching device, it must be flushed from time to time to remove what is captured. This is a necessary box to check during any maintenance, but must be done with caution. Every time fluid is taken out of a system blowing down a dirt separator, you’re bringing new fluid in — just like that leaking system previously noted.
This fresh water or fluid will include more oxygen that needs to be removed by a mechanical device such as an air separator or consumed by the corrosion process. Corrosion means more magnetite, and the vicious cycle continues.
Another thing to consider in your quest to clean up hydronic systems is the possibility that the debris may never make it to your dirt separator. In most cases, with properly sized circulators, piping will be seeing velocities somewhere between 2 to 4 feet per second in residential and light commercial applications. This is adequate to move entrained air and microbubbles through your system, but falls short when it comes to flushing out debris, which usually needs velocities in excess of 5 feet per second.
It’s also good to point out that if you’re using a fill valve to fill and purge your systems, it’s probably not going to cut it for debris either. This is where you’ll need to invest in a good utility pump or flush cart, increase velocities and show that dirt who is boss! Maybe we can discuss that in the future?
What I would like for readers to take away from this column is that as long as hydronic systems exist, dirt and debris will continue to keep us on our toes. Dirt can come from a number of different places, not just installation. It can be the problem and also the symptom of a much larger problem. Likewise with dirt and magnetic separators; they may be the solution or the first step toward a cleaner system.
Not only do you possess the ability to make the system more reliable by cleaning it up, but you also can increase efficiency as heat transfer will benefit, too. What customer wouldn’t want a system that’s more reliable and efficient?