The Soft Option – Calorifiers and Hot Water Storage In Corrosive Water Conditions

For many commercial organisations, the assured availability of sustainable hot water is a business-critical issue, but one that can quickly become costly for those operating in the southwest and northwest of the UK, the Welsh coast and throughout Scotland. With a low pH, low total dissolved solids (TDS) and negligible buffering capacity, these naturally soft water areas prove highly corrosive to glass-lined vessels typically used in hot water systems.

Glass is, given the right conditions, generally resistant to attack from most chemicals and corrosive materials and easier to clean, making it a popular choice for lining steel vessels used in hot water systems. But corrosion is a complex phenomenon, and in naturally soft water conditions, despite use of sacrificial anodes, glass-lined vessels can rapidly succumb to critical corrosive damage

Pressure to Perform

In addition, the taller the structure, the greater the pressure requirements on the system, particularly since a common design choice is to locate the plant room in the basement. In order to meet, even small demands with a consistent, strong flow of hot water systems inevitably are oversized, adopting a larger, often bespoke tank.

This immediately exacerbates the existing threat, as oversizing, or the failure to correctly balance water flow also contributes to system corrosion. Oversizing of the pumps leads to high-velocity hot water circulating through the system and suspended solids in the water are driven against the metal leading to erosional corrosion. This process helps accelerate the soft water corrosion at points where water changes direction, such as when passing into or through tanks.

Glass-lined water vessels under these conditions can potentially fail due to corrosion in a matter of just months – even with the use of sacrificial anodes. For these reasons, manufacturers will reduce or have even ceased to offer warranties on glass-lined products installed in these soft water regions. As a result, their specification into projects in these regions really can be a false economy.

Glass Lined or Stainless Steel?

Far more resistant to these water-side assaults are stainless steel vessels. Although there is a higher upfront cost, this would be easily offset by the relative longevity of the appliance. However, projects with smaller, yet higher pressure hot water demands, will still face the issue of oversizing. This further extends capital costs, of products, installation and the need for greater plant room space. As a result, project costs can become prohibitive for stainless steel, resulting in the specifying of the less expensive glass-lined alternatives gambling that they will prove resistant enough in the mid-long term.

Adveco addresses these concerns with its ATSx range of compact stainless steel, high-pressure hot water tanks. Specifically designed to serve as buffer vessels and indirect hot water calorifiers suitable for use with lower capacity, high-pressure commercial applications in soft water areas. The ATSx range provides specifiers and contractors with a wide choice of vessels all rated to 10 bar as standard, which are by far the most efficient and cost-effective choice for businesses with smaller system demands.

Another advantage provided by the indirect water heaters in this range (ATSI, ATST, ATSH, and ATSR) is that due to the transferral of heat through the walls of the heat exchanger element the two fluids do not mix. This allows for more options in terms of the external heat supply and introduces a range of renewable technologies that use other fluids for heat transfer including solar thermal collectors and ASHPs. The twin coil ATSR has been specifically designed for these lower-temperature renewable applications. These calorifiers are also relatively simple to install, since there is no burner, there is no need for a gas supply to be directly connected to the appliance and the is no requirement for a flue.

As with any hot water application, understanding the relationship between storage and recovery, and correct sizing is extremely important for efficient and cost-effective operation.

Integrating a stainless steel calorifier within a hot water system gives you a number of design options, with a large efficient boiler a calorifier can be smaller avoiding unnecessary capital and ongoing operational expenditure. At 200 to 1000 litres the ATSx range provides a compact, tough resolution for lower demands applications in those soft water areas. If your project has pressure requirements greater than six bar, then the ATSx vessels are by far the most efficient and cost-effective choice for your project.

If the boiler is smaller, or demands for hot water are greater, then going too small means the storage could prove inadequate and the system will not achieve its operational requirements. For projects with larger demands or requiring greater customisation Adveco can support the project with the SSB, SSI and SST ranges of bespoke stainless steel calorifiers and buffer vessels.


Water Hardness

Parts Per Million (PPM)             Softness / Hardness

0 – 50 PPM                               Soft

51 – 100PPM                            Moderately Soft

101-150PPM                             Slightly Hard

151 – 200PPM                          Moderately Hard

201-275PPM                             Hard

276-350PPM                             Very Hard

350+PPM                                  Aggressively Hard



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