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Stainless steel or aluminium?

What's best when it comes to heating your school?

Posted by Hannah Vickers | August 12, 2017 | HVAC & lighting

By Steven Evans, National sales manager for Potterton Commercial

There is an ongoing debate in the heating industry over the merits of stainless steel and aluminium heat exchangers. Most manufacturers stick to a single material, believing it is superior to the other. However, Potterton Commercial’s product portfolio features both. 

With the school holidays in full swing, many school facility managers will have already planned upgrade and or maintenance work into their schedule. However, the conflicting information from different manufacturers regarding heat exchanger materials can often make choosing a new boiler a confusing process. Although many boiler manufacturers use either stainless steel or aluminium for their heat exchangers across their entire product line, Potterton Commercial uses both.

There is no conclusive evidence that stainless steel is more reliable or longer lasting than aluminium, or vice versa, so we see no reason to choose one over the other

There is no conclusive evidence that stainless steel is more reliable or longer lasting than aluminium, or vice versa, so we see no reason to choose one over the other. For example, our Sirius range has stainless steel heat exchangers, whilst our Paramount four and Eurocondense boilers use aluminium. Because we work with both materials, we believe we are in a unique, unbiased position to explain the benefits of each one to our customers. 

Stainless steel

Stainless steel has gained an excellent reputation due to its wide spread use in hi-tech products and modern domestic appliances. However, it’s important to remember that the performance of this material does vary, as it depends on the amount of chromium it contains. Stainless steel is essentially low carbon steel containing chromium at 10.5% or more by weight, and it is the addition of chromium that gives stainless steel its unique corrosion resistant properties. The quality of stainless steel is dependent on its grade – at Potterton Commercial we use 316L - this is a high-grade that provides strength, reliability and performance.

As high-grade stainless steel is robust, it is often chosen as a heat exchanger material because it reacts very little to contaminants in system water

As high-grade stainless steel is robust, it is often chosen as a heat exchanger material because it reacts very little to contaminants in system water. One example of a contaminant is sea salt, and for this reason we would recommend boilers with stainless steel heat exchangers for schools in coastal areas.

Aluminium

Aluminium has gained an equally impressive reputation because of its widespread use in the automotive industry for the manufacture of engines and car bodies. Since aluminium features a corrosion-resistant protective oxide coating, it can effectively reduce the risk of rust – hence its popularity within the car making industry. 

Aluminium was used in the first condensing boilers ever produced, and there is already over 35 years of experience of aluminium-based heat exchangers in the industry. Many boiler manufacturers find the material flexible and versatile; indeed, one of its main benefits is that it can be cast, increasing the design possibilities.

Potterton Commercial uses cast aluminium heat exchangers produced at our own foundry in Preston, Lancashire. This means we can benefit from having unique flexibility in the design of modern aluminium heat exchangers. Having full control of the manufacturing process enables our design teams to optimise heat exchanger and boiler component integration/space efficiency at a more competitive cost. 

In addition to flexibility, aluminium also offers excellent thermal capacity, meaning water can move more slowly around the system and the return water temperatures are cooler, increasing efficiency

In addition to flexibility, aluminium also offers excellent thermal capacity, meaning water can move more slowly around the system and the return water temperatures are cooler, increasing efficiency.

Regardless of the choice of heat exchanger material, maintaining the quality of the water circulating through a heating system is essential. All boilers will perform more efficiently and reliably with good-quality water circulating in them. The system water should always be chemically treated to maintain the correct pH level and reduce dissolved atmospheric gases which, if left untreated, will result in corrosion and the build-up of limescale.

Systems that are corroded become blocked with sludge and debris, which cause the boiler to work harder for longer as the circulating water is unable to transfer the heat efficiently throughout the system. Limescale deposits on heat transfer surfaces also reduce efficiency, because the boiler will need to run at a higher temperature for longer.

Chemical water treatment should therefore be incorporated at the commissioning stage and included in ongoing planned maintenance. The water treatment programme should comprise a system clean/flush and regular doses of inhibitor as required.          

Considering that both stainless steel and aluminium have excellent properties, the differentiation between boilers is not just based on which heat exchanger materials are used. How the components are applied and how they work together within the boiler are also key in determining the performance of a boiler. 

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