Filling hydronic systems with demineralized water?


Old 07-29-16, 06:45 PM
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Filling hydronic systems with demineralized water?

John Siegenthaler, a noted expert on hydronic heating, has a monthly column in PME magazine. The July 2016 edition has a special report, with an article by Siegenthaler, "Water Quality Matters." He recommends that demineralized water be used in hydronic systems. For smaller systems, fill them with demin water. For larger systems, he recommends an ion-exchange column as a side-stream device with continuous flow provided by the circulator pump.

Wow, this comes as a surprise to me. My 65-year-old, steel, fire-tube, residential, hot water boiler has always used plain city water. Filling it with demin water wouldn't be too convenient every time it is drained for maintenance. A side-stream, resin-type ion exchanger would be a bit complicated considering the need to regenerate the resin.

I've reread the article, thinking perhaps I misunderstood, but I don't think so.
Old 07-29-16, 07:45 PM
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Whats your point? My boiler is some 50 yrs old and on well water...

Johns a good guy but show me the yrs and yrs of water tests on boilers and their longevity....

Aint none probably as all water and boilers per location are different IMO...

Im sure joel will chime in...

Your post is open ended really....
Old 08-01-16, 08:18 AM
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Isn't there a pill for that?
Kidding aside, in the automotive sector there are additives in the oil that help with ph, carbon, dirt, etc. In the cooling system there are additives to the glycol that do much the same, plus help keep galvanic corrosion at bay in engines comprised of steel, brass and aluminum parts.

Why do we use untreated tap water in home heating?

AFAIK my 40 year old cottage system has the original glycol in it. Previous owner claimed it has never been serviced.
Old 08-01-16, 11:08 AM
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The worst thing for water in a closed loop system such as a hydronic heating system is oxygen. Keep the oxygen out and you can forget about it.

Unfortunately, that is far easier said than done. Leaks are the primary source of oxygen because the "make up" water is usually saturated with oxygen in solution. Eliminating the leaks and eliminating the make up water is the ideal.

There are several chemical treatments available to control both scaling and corrosion. They are rarely used in residential systems because most are toxic to human health requiring backflow prevention devices on the make up water system. These backflow devices are more complex than the usual Watts 9-D device and often require annual testing and a cost. Further, few homeowners are diligent in testing the chemical concentrations of the system which often leads to lower chemical levels and as false sense of security that the piping is being protected.

For most residential systems there is no need for using anything other than potable (drinking quality) water.
Old 08-01-16, 04:38 PM
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My 65-year-old hydronic system is piped with black steel pipe. When I open or cut into the piping for modifications (such as replacing valves, adding a low-water cutoff, etc.), the inside wall of the pipe is completely free of scale or corrosion.

I have a conventional expansion tank with B&G Airtrol fittings that continually remove any air from the circulating water, and return it to the tank. Leakage is essentially zero - during the summer, I isolate the connection to the automatic fill valve from the city water supply, and the system pressure does not decline at all. There have never been any additives used with the water.

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