Scale in plumbing systems is a common and stubborn problem that arises from the buildup of mineral deposits, primarily calcium, and magnesium salts. This can be problematic to the overall performance of a system as, “the accumulation of scale within pipes, valves, and fixtures directly compromises the structural integrity of a building’s plumbing network,” according to Di Jiang, product specialist at Watts Water Technologies.
Scale prevention is critical for maintaining the performance of plumbing systems, enhancing water quality and improving flow rates. Scale residue not only affects water quality, and the physical appearance of fixtures and pipes but, “It acts as an insulating barrier, leading to several detrimental effects. It can constrict the internal diameter of pipes, resulting in reduced flow rates and increased pressure loss, ultimately diminishing energy efficiency,” adds Jiang.
Understanding Scale
Scale, also known as limescale, is the visible white chalky substance that is formed when hard water evaporates. “Hard water contains high concentrations of minerals such as calcium and magnesium. When heated or allowed to evaporate, these minerals precipitate out of solution and cling to surfaces, gradually forming scale,” explains Kirk Nagus, general manager at Axiom.
When determining the first symptoms of scale buildup, “Initial indications of scale buildup in a heating system often manifest as heightened energy consumption or a noticeable decrease in radiator temperatures,” says David Holley, technical manager of chemistry at Fernox. “To verify the potential formation of scale, a chemical analysis of the system water can be conducted and compared to the water initially used to fill the system.”
When talking about anything related to scale, water quality within a piping system is the first and most important step as, “Keeping water clean in today’s high-efficiency systems with smaller passageways is absolutely vital. Even the smallest layering of scale on system pipework can cause efficiency reductions,” said Antonia Aldridge, marketing and sales manager at Adey North America. Once a piping system has scale accumulation, it can negatively impact water quality in a multitude of ways, such as reduced flow rates and pipe corrosion. Aldridge adds that, “If you are in a hard water area, your system is more likely to suffer from scale buildup.”
Any scale prevention method should start by focusing on water quality. “For residential water treatment,
nothing takes the place of or saves more time and aggravation than commissioning a reliable water analysis. Knowing what’s in the water is the first step towards knowing how to treat it properly,” said Jiang.
Nagus adds, “Water quality is the lifeblood of a heating and cooling system. If you don’t start there, that’s a detriment to every mechanical piece of equipment and the piping in the system. Conducting regular water quality tests on the site water prior to filling a system is crucial in determining the water supply’s composition. This information can help plumbers identify the most appropriate scale prevention methods for each specific situation.”
Getting ahead of scale
When combating the issues caused by scale formation, proven methods include water softening, scale inhibitors, and descaling devices. As Jiang explains, “There are many ways that water can pose ongoing issues within a home’s piping system, but in terms of overall cost, water hardness surely takes the prize. A traditional water softener operates through a process known as ion exchange. Within the softener, ion exchange resins swap the hardness ions, primarily calcium and magnesium, with sodium ions. This action leads to the retention of hardness ions within the resin bed. Once the resin reaches capacity, through the regeneration process with salt water, the captured hardness ions get ejected back into wastewater and the resin bed gets refreshed.”
A great way to keep on top of system health is to “check the water conditions regularly. This can include using hardness strips to test for scale, pH strips to test for pH levels (which should be between 6.5 and 8.5), and corrosion strips to test for corrosion in the system too,” explains Aldridge.
Nagus adds, “After you start with good water quality, you can use scale inhibitors to stop corrosion. Scale inhibitors form a thin protective layer that prevents the adhesion and crystallization of scale-forming minerals, thereby reducing scale buildup.”
However, there are risks associated with scale prevention methods such as water softening. “The risk of installing a water softener on a domestic/potable system is the water becoming more aggressive. That’s because sodium ions replace calcium and magnesium ions which increases the conductivity of the water. High conductivity levels also lead to scale formation” said Aldridge.
Jiang also explains that the, “Continuous introduction of chemicals leads to ongoing monthly costs for end users and the disposal of wastewater containing an elevated amount of sodium chloride can impact the environment.”
Francine Wickham, Fernox’s global marketing director adds, “We do not recommend artificially softened water in heating systems because the pH can rise rapidly, damaging the aluminum heating components. Rather, we advocate for corrosion inhibitors and antifreeze water treatment products.” There are eco-friendly alternatives to traditional scale prevention methods.
Closed vs. open loop
Scale accumulation and prevention differs depending on the type of plumbing system. As Nagus explains, “A closed-loop system circulates water within a self-contained piping network, such as a hot water heating system. In an open-loop plumbing system, water is continually drawn from a natural water source and supplied to the plumbing fixtures. Open-loop systems are commonly used for irrigation purposes or in cooling towers, where water is used to transfer heat.”
Closed loop systems typically consist of a boiler, heat exchanger, and radiators and, “Scale formation typically occurs within the hottest components of the heating system, primarily on the surface of a heat exchanger,” explains Holley.
“As scale accumulates on the heat exchanger’s surface, it reduces heat transfer efficiency from the heat source to the water. Essentially, a layer of scale acts as an insulating barrier between the heat source and the water being heated, resulting in increased energy consumption for water heating. This occurs because scale is a significantly poorer conductor of heat compared to the metals or alloys used in heat exchanger construction.”
Going further into scale buildup in a closed-loop hydronic system, “The number one sign of scale buildup in the system is a noisy boiler. Scale buildup will have a huge impact on heat transfer. This is why ensuring a system has good quality water is important, as what’s the point in installing a 95 or 96 per cent efficient boiler when the water running through it lowers those efficiency ratings? Due to these heat transfer issues, the end-user will see increased utility bills because the system is working harder to provide the same amount of heat,” explains Aldridge.
Nagus adds that, “When you design or install a closed system like a boiler loop, you’re not bound by the standards associated with potable water, and when I say potable water, that means drinking water because the water you’re putting into it is being utilized to distribute heat and be recirculated through the system over and over and over again. This is one of the main differences between open and closed loop systems — there are different metals and materials you can or can’t use.”
Additionally, “Scale prevention strategies for open-loop systems primarily focus on removing or neutralizing the mineral content of the water, preventing it from forming a crusty buildup within the system,” said Nagus. :