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Understanding magnetite in hydronic heating systems: 5 FAQs answered
What is magnetite?
Magnetite is a type of iron oxide mineral that forms when iron reacts with oxygen. In the context of hydronic heating systems, magnetite forms as a byproduct of corrosion. When water (often oxygenated) interacts with steel or iron components within the system, it causes a chemical reaction that produces iron oxides. One of these oxides is magnetite.
Unlike rust (Fe2O3), which is reddish-brown and flaky, magnetite (Fe3O4) has a more compact, dense structure, making it harder to detect and remove. Over time, magnetite particles can build up in the system's water, causing a sludge-like substance that circulates with the flow of water.
What role does the water’s pH value play in the formation of magnetite?
The pH level of water in a hydronic heating system plays a significant role in the formation, stability, and behavior of magnetite. pH is a measure of how acidic or alkaline (basic) a substance is, with a scale ranging from 0 (highly acidic) to 14 (highly alkaline). Neutral water has a pH of 7. The pH value of water affects corrosion due to the electrical conductivity of water. Both low (< 7) and high (> 10) pH values increase electrical conductivity.
Acidic water (pH < 7) accelerates the corrosion of steel and iron components. Increased corrosion means more iron is released into the water, which can promote the production of both red rust and magnetite. Highly alkaline water (pH > 9,5), on the other hand, can cause the protective oxide layer on metal surfaces to break down. This potentially causes localised corrosion, leading to the release of more iron and promoting magnetite growth. While neutral water might seem ideal, it can still contribute to corrosion, especially if it contains dissolved oxygen. Oxygen reacts with iron to produce iron oxides, including magnetite.
In a hydronic heating system mildly alkaline water (pH 8,0 to 9,0) is therefore typically preferred. This pH range encourages the formation of a stable, protective oxide layer on system components, reducing the amount of free iron that can turn into magnetite. Modern hydronic systems often use corrosion inhibitors and pH buffers to keep water within this optimal range. However, routine checks of pH levels are essential for optimal system operation. Too much acidity or alkalinity can lead to corrosion, magnetite buildup, and overall system inefficiency.
How does magnetite usually get into a hydronic heating system?
If the heating system has or has had leaks and water has been added to the network, the added water brings in oxygen that binds to the steel surfaces. The formation of magnetite can also be due to the wrong piping material that lacks an oxygen diffusion barrier. Over time, this fine rust detaches into the heating water and begins to accumulate at the bottom of the radiators. Under such a sediment layer, conditions can arise where anaerobic bacterial activity may corrode the steel and cause leaks.
Does magnetite cause problems in a hydronic heating system?
A small amount of magnetite in the heating network doesn’t cause practical problems. It also acts as an insulating layer protecting the internal steel surfaces of the radiator. If the magnetite accumulates, however, several problems may arise, including corrosion, blockages and increased wear.
After all, magnetite is formed when iron reacts with oxygen in the system water, which can lead to corrosion in the pipes and other components. It can also erode connection elbows, valves and pumps, leading to increased wear and a shortened lifespan of these system components. Moreover, magnetite is heavier than water, so it tends to settle in the pipes and radiators. When it does, this can restrict or block the water flow.
Does magnetite affect the heat output of a radiator?
Yes, magnetite can significantly reduce the heat output of a radiator. As magnetite builds up inside a hydronic heating system, it causes blockages of the radiator channels. This prevents hot water from circulating properly, resulting in cold spots at the bottom of the radiator while the top may still feel warm. This uneven heating reduces the overall effectiveness of the radiator. Moreover, the magnetite particles in the system circulate to other system components as well, such as valves, thermostatic radiator valves (TRVs), and small pipes. Gradually, these get clogged and deliver less hot water to the radiator. This in turn lowers the radiator’s ability to heat up the room effectively and increases pump strain, overall system inefficiency and energy consumption.
Additionally, as magnetite settles on the internal surfaces of radiators, it forms a layer of sludge. This sludge acts as an insulator, reducing the efficiency of heat transfer from hot water to the outer surface of the radiator. As a result, the radiator surface stays cooler than it should, meaning less heat is emitted into the room. The heating system has to work harder and consume more energy to maintain the desired room temperature.
How can I fix and prevent magnetite buildup in a hydronic heating system?
Power flushing is a commonly used technique to dislodge and remove magnetite from a hydronic heating system. This involves using a high-pressure pump to force water, along with cleaning chemicals, through the system at high velocity. The high-speed flow dislodges magnetite sludge and other debris, flushing it out of radiators, pipes, and heat exchangers. Sometimes chemical cleaners are added to the heating system water to break down and dissolve magnetite and other debris. The cleaning agents loosen deposits of magnetite from internal surfaces, after which the system is drained to remove the contaminated water.
To prevent magnetite buildup, you can install a magnetic filter on the heating system’s return pipe. This device captures and traps magnetite particles as water flows through the filter, preventing them from recirculating in the system. The use of a magnetic filter prevents further buildup, protects the boiler, reduces strain on the pump, and extends system lifespan. The filter should be checked and cleaned during annual system maintenance.
For an optimal result in larger heating systems, we recommend combining a magnetic filter with a degasser to effectively remove the gases that cause corrosion. After all, the air in the system contains about 20% oxygen and this reacts very quickly with the steel in the radiator when you fill the system with water. There is always air in the system, meaning that magnetite will continue to form. A degasser is then a very efficient solution to prevent the gases from reacting with the steel.
As mentioned above, maintaining the right pH level in the system water also prevents excessive corrosion and magnetite production. It’s recommended to test the pH of the system water annually or after any major system changes, such as a water drain and refill.
Finally, routine system checks can catch early signs of magnetite buildup. Regular system maintenance allows for quick intervention and ensure the radiators can operate efficiently at all times. Look for cold spots on radiators, noisy pipes, and slower heating performance, all of which are signs of magnetite issues.
If you have any other questions about magnetite in hydronic heating systems, don’t hesitate to get in touch with our experts. We are happy to help in any way we can.