With older, lower efficiency cast iron boilers, water chemistry was generally not a major concern. However with today’s higher efficiency modulating/condensing boilers, water quality is a concern.
These new boilers have much smaller water volumes and are constructed from metals much different than cast iron and therefore must be protected.
Do not use water treated with salt bedding type water softeners. Tap water may be used. If it exceeds a pH of 8.5 or a hardness of 7 grains per gallon or higher, it must be pre-treated. Sentinel X-100 Inhibitor can be used if the pH is below 7.
For water hardness higher than 7 grains per gallon it can be demineralized by pumping it through a de-mineralizer, such as manufactured by Axiom. Another option would be to purchase distilled water from a local water supplier.
Follow the boiler manufacturer’s recommendation for any specifics on anti-freeze. Typically, they will recommend an inhibited propylene glycol. Corrosion inhibitors vary by the metals they are designed to protect, and the boiler manufacturer may recommend specific brands.
The source for this Tech Tip: Buderus Technical service bulletin “Boiler Water Chemistry and Freeze Prevention Guidelines”
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