Can Aluminum Boilers 'Play Nice' with Other metals?

Alloys of aluminum are being implemented in heat transfer applications, including hot water boilers, more frequently due to aluminum’s very high conductance of heat. However, aluminum is much more expensive and highly reactive when compared to standard materials used in these applications, such as steel.

Knowledge Direct

Want to share this topic and more with your team?

While the use of these alloys can provide improvements to heat transfer efficiency for hot water boilers and heat exchangers, a proper water treatment program tailored to minimize corrosion of aluminum while maintaining protection of other metals within the system is critical. The decision to implement such equipment must be made by balancing the potential savings through reduced utilities consumption or shortened cycle times against the increased risk of system damage and premature failure due to the reactive nature of aluminum alloys.

pH Control

The most critical factor to protecting aluminum within a water system is maintaining pH within the stable range for aluminum.


Aluminum forms a naturally protective barrier of aluminum oxide on the metal surface, but this oxide film is only stable in a pH range of approximately 4.0 to 8.5. Outside of this range, the oxide film can begin to degrade. Once the film degrades, even in a small area, the exposed aluminum beneath will corrode much more rapidly, resulting in what is known as pitting. This pitting is much more aggressive under alkaline conditions, which is typical of most water systems which have been treated with a standard corrosion inhibitor blend. This is because steel and most other metals commonly found in water systems are more stable and protected from corrosion under more alkaline conditions.


Thus, to maintain protection of the entire system, the pH must be controlled within the stable range for aluminum, while maintaining an adequate level of corrosion inhibition for any other materials in use.

Corrosion Inhibitors

As with any water system, corrosion inhibitors are required to minimize corrosion rates on the metals within the system. However, when systems contain aluminum, the inhibitor to be used must be selected with careful consideration to ensure that all materials in use are protected. 

Any inhibitor selected must be buffered to near neutral pH, and, dependent upon the pH of the raw water being used to make up the system volume, additional buffering solution may be required to bring pH to within a stable range, typically pH 5.0-8.0. There are many corrosion inhibitor chemistries that will provide adequate protection from corrosion for steel and other metallurgies while maintaining pH within the acceptable range to minimize corrosion of aluminum.


There are additional considerations if the water system also contains copper, brass, or any other yellow metal, as the protection of these materials is also critical to maintaining corrosion resistance of aluminum. Any corrosion of these materials may result in copper ions being released into the water, which, when contacting any aluminum surface, will result in severe pitting. Therefore, appropriate inhibitors must be present to prevent the corrosion of these materials to ensure protection of both the yellow metals and the aluminum.

Galvanic Separation

As previously mentioned, aluminum is a highly reactive metal, being one of the more anodic metals on the galvanic series. As such, it is very important to maintain galvanic separation between aluminum within the system and any other metal, particularly those which are more cathodic than aluminum, namely copper and brass alloys. 

If aluminum is directly connected to other metals, a galvanic cell will form, which will result in rapid corrosion. Aluminum, acting as the anode, will experience significant degradation and loss of material, eventually leading to failure.


Steps should be taken to minimize or eliminate the use of copper and brass alloys in a system which contains aluminum wherever possible, or at the very least, ensuring that these metals are galvanically separated from the aluminum. This can be achieved using dielectric fittings, or other means of separation, such as a buffer of PVC pipe or other non-reactive material between the aluminum and other metals.


The decision to implement aluminum boilers, or other heat exchange equipment containing aluminum alloys within a water system, must be made in a thoughtful way. While aluminum may provide potential savings through improved heat transfer efficiency, this must be balanced with the requirements of the metallurgy throughout the system. Great care must be taken to control water chemistry, particularly pH, to ensure any efficiency gains are not negated by damage to other system components. If you have aluminum components within any of your water systems, consult your water treatment professional to ensure that your treatment program is providing the right protection for your system.


Enjoy Reading This? Why Not Share It With Other’s

Share on facebook
Share on twitter
Share on linkedin
Share on google

Knowledge Direct

Want to share this topic and more with your team?

Related Posts

Wasting Money
Boiler Water Treatment

Your Offline Boiler May Be Costing You Money!

Offline periods can damage your boiler, decreasing its useful life and increasing maintenance and repair costs. With proper planning and preparation, a boiler can be safely taken offline with a procedure known as a boiler layup.

Read More »
Element Aluminum
Boiler Water Treatment

Can Aluminum Boilers ‘Play Nice’ With Other Metals?

Aluminum is becoming more common for use in heat transfer applications due to its very high conductance of heat. However, aluminum is highly reactive when compared to other materials such as steel, requiring a specialized treatment program to minimize corrosion of aluminum while maintaining protection of other metals.

Read More »

Leave a Reply

Request Access

Download Report – Best Practices for Energy Efficient Boiler Plan Design, Operation and Control

On-Site Seminar Request Form

Checklist for Minimizing Legionella Risk Download (2018)

St. Mary Mercy Livonia Hospital Case Study

Head Office

Access Request

Legionnaires’ Disease Guide for Employers and Building Owners Download

Aqua Analytics DK-12000 Download

Checklist for Minimizing Legionella Risk Download

Purchaser Checklist for Setting Base Case Scenario Download

Engineering Notes – Deaerator Download

Tower & Chiller Lay-Up Procedure Download

Blog Newsletter Subscription

Contact Me

Service Locations

Ohio Sales Office

Michigan Sales Office

American Head Office