In commercial and industrial buildings, closed-loop heating and chilled water systems are vital for maintaining comfortable indoor environments and ensuring energy efficiency. These systems circulate water or water-glycol mixtures through pipework, radiators, fan coil units, or air handling equipment to deliver heating or cooling where it’s needed. Yet despite the sophisticated design of boilers, chillers, pumps, and controls, there’s one often-overlooked but essential component that keeps these systems running reliably: the dosing pot.
Despite its small size and simple appearance, a dosing pot plays a critical role in maintaining water quality, protecting expensive system components, and extending the operational life of heating and cooling installations. Without it, facilities risk higher maintenance costs, lower energy efficiency, and even premature system failure.
What is a Dosing Pot?
A dosing pot, sometimes referred to as a chemical dosing unit, chemical pot, or dosing vessel, is a sealed chamber installed on closed-loop heating or chilled water systems. Its purpose is to allow maintenance teams to introduce corrosion inhibitors, biocides, antifreeze, and other water treatment chemicals into the system safely and accurately.
Because these systems are sealed and pressurised, simply adding chemicals directly into the circuit isn’t practical—or safe. Doing so would often require shutting down parts of the system, depressurising pipework, and risking exposure to hazardous substances. By using a dosing pot, engineers can add chemicals without disrupting operation, ensuring minimal downtime and better safety for maintenance staff.
Preventing Corrosion and Bacterial Growth
One of the main reasons dosing pots are so important is their role in corrosion prevention. Over time, untreated or poorly treated water in a closed-loop system can corrode pipes, pumps, heat exchangers, valves, and other metallic components. Corrosion leads to reduced system efficiency, increased maintenance costs, and a higher likelihood of costly breakdowns. Corroded systems can suffer from pinhole leaks, debris clogging strainers or heat exchangers, and eventual structural failure of key components.
By adding corrosion inhibitors through a dosing pot, facilities can protect the metallic elements within the system, ensuring they remain intact and functional for years to come.
Bacterial growth, particularly in chilled water systems, is another common concern. Microorganisms can thrive in stagnant or inadequately treated water, leading to biofilm formation. This slimy layer not only reduces heat transfer efficiency but can also cause microbiologically influenced corrosion (MIC), which accelerates damage to metal surfaces. In some settings—such as hospitals, schools, or offices—uncontrolled bacterial growth can pose a risk to health and safety. Regularly adding biocides through a dosing pot helps maintain hygienic water conditions, preventing the spread of harmful bacteria before they become a serious problem.
How Does a Dosing Pot Work?
Another advantage of a dosing pot is its straightforward design and safe operation. Typically, a dosing pot is installed in a bypass loop across the main pipework of the heating or chilled water circuit. This bypass arrangement features isolating valves that allow engineers to close the flow of water through the pot, open it safely, and fill it with the required treatment chemicals.
Once filled, the valves are reopened, and the circulating pump in the system mixes the contents of the dosing pot evenly throughout the entire circuit. This ensures accurate, controlled dosing and prevents the uneven distribution of chemicals, which could leave some parts of the system under-treated.
Many dosing pots feature sight glasses so maintenance teams can monitor the pot’s contents, as well as vent valves to remove trapped air, fill valves for adding chemicals, and drain valves for flushing. These components allow safe, efficient, and accurate dosing with minimal risk to personnel.
Choosing the Right Dosing Pot
Selecting the appropriate dosing pot for a system is crucial to achieving effective water treatment. Factors to consider include the total volume of the system, the types and concentrations of chemicals to be dosed, and the pressure and temperature ratings of the closed-loop circuit.
Common dosing pot sizes range from compact 3.5-litre models suitable for smaller commercial systems to larger 25-litre units or bespoke solutions for expansive industrial heating or cooling networks.
Material selection is equally important:
- Carbon Steel: Often chosen for budget-friendly installations but less corrosion-resistant, making it suitable only for systems with effective ongoing treatment.
- Stainless Steel: Offers superior corrosion resistance, durability, and longevity, making it ideal for high-specification commercial and industrial systems, or systems operating with aggressive water conditions.
When choosing a dosing pot, it’s also important to ensure the pot comes with all necessary accessories, including a safety relief valve, pressure-rated connections, and durable isolation valves. This ensures compatibility with modern heating and chilled water systems and compliance with health and safety standards.
Efficiency and Sustainability Benefits
Using a dosing pot regularly to maintain optimal water chemistry does more than protect pipes and equipment—it directly contributes to system efficiency. Corrosion, scale, and bacterial fouling all reduce the ability of heat exchangers, radiators, or fan coils to transfer heat effectively. This forces boilers or chillers to work harder to maintain desired indoor temperatures, increasing energy consumption and utility costs.
By keeping heat transfer surfaces clean, properly treated systems operate more efficiently, resulting in lower energy bills and reduced carbon emissions. This is particularly important for organisations with sustainability goals, carbon reduction targets, or corporate social responsibility commitments.
Furthermore, extending the life of existing heating and chilled water systems through effective water treatment reduces the environmental impact associated with premature replacement of large pieces of mechanical plant.
Maintenance and Best Practices
To maximise the benefits of a dosing pot, it’s essential to use it as part of a comprehensive water treatment and maintenance strategy. This includes:
- Regular Testing: Periodic sampling and analysis of system water to monitor pH, conductivity, inhibitor levels, and bacterial counts.
- Scheduled Dosing: Adding chemicals according to the system’s treatment plan, not just when problems arise.
- Documentation: Keeping clear records of dosing schedules, water test results, and maintenance activities.
- Professional Support: Working with qualified water treatment specialists to design and monitor the treatment regime.
Where to Find Quality Dosing Pots
For anyone responsible for the design, installation, or maintenance of heating and chilled water systems, choosing the right dosing pot and using it correctly is essential. Quality dosing pots should be pressure-rated to match system specifications and constructed from durable materials suitable for years of reliable use.
Leading suppliers, such as Stourflex, offer robust dosing pots with clear sight glasses, easy-to-operate venting and filling valves, and rugged construction to withstand demanding commercial and industrial environments. These manufacturers also provide expert guidance on selecting the right size and configuration for your system, ensuring optimal performance and long-term reliability.
Conclusion: A Small Component with a Big Impact
Though it may seem minor compared to boilers, chillers, or large pumps, a dosing pot plays a major role in the health and efficiency of modern closed-loop heating and chilled water systems. By allowing safe, accurate dosing of water treatment chemicals, a dosing pot helps prevent corrosion, control bacteria, improve system efficiency, and extend equipment lifespan.
For building owners, facilities managers, and maintenance teams, investing in the right dosing pot—and using it as part of a proactive water treatment programme—is one of the smartest ways to protect your heating and cooling systems, reduce costs, and promote sustainable, energy-efficient operation.
