Over the past several years, aluminum heat exchangers are being used increasingly in closed hot water loops with hot water boilers.  The manufacturers of these hot-water boilers usually recommend the pH specifications for the fluid circulating through these aluminum heat exchangers.  The typical stated pH range is 6.0 to 8.5 to prevent corrosion of the aluminum in the system. With these systems, controlling the pH within the desired range is critical for controlling aluminum corrosion. Typically, a closed hot water loop will have a mix of metallurgies including steel and copper in addition to the aluminum heat exchanger.  Both steel and copper corrosion rates would climb if the pH of the system were in the 6 – 7 range.  Therefore, it is desirable to maintain the pH near the high end of the range (8.5) to accommodate all the metallurgy of a given system.  Another consideration is that aluminum is much less noble than steel or copper, so di-electric unions must be used to protect the aluminum from galvanic corrosion. Proper startup and program conversion are also critical for systems with aluminum heat exchangers.  Traditional chemistries for cleaning and startup are alkaline, phosphate based formulations.  Unless the boiler can be isolated during construction cleaning, a different style clean and flush procedure needs to be used. To learn more about water treatment solutions for hot-water boilers using aluminum heat exchangers, contact Summit Laboratories, your water treatment solutions experts in Denver, Colorado, at 303-293-9862.