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Frostproof Hydronic System

Jack, CVMS
Jack, CVMS Member Posts: 81
First, let me point out that my perspective is that of someone living in a part of Alaska with temperatures similar to those in Fairbanks, so make suitable adjustments for your area..
We fill most systems with a 35% mix of Dowfrost (95% inhibited propylene glycol) and 65% deionized water. This provides freeze (slushing) protection to 4° F, and burst protection to -60°F. If we know a home will be shut down for the winter season, we will use a stronger solution, but for over 90% of the homes, the 35% solution is fine.
Rather than attempt to compute the system capacity, we mix the solution beforehand and, after draining and blowing out as much as possible from the system, we pump in the new solution. In an older system, we will usually install a cleaner a week or so ahead of time so that the system will be in good shape for the new solution. Naturally, it is flushed thoroughly before the glycol solution is installed. In addition, since there is always a little residual water left in the system after blowing it out, we "sweeten" the solution with a gallon or so of pure Dowfrost, and check the final results with a refractometer after it has circulated for a while.


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