THE NEWSMAGAZINE OF MECHANICAL CONTRACTING Reprint from November 1994

changer to the manifold and the How to stop rubber and secondary loop . All of these components are available system corrosion in 316 stainless steel except mani- folds for which brass or copper is BY JOE FIEDRICH diffusion barriers on non- acceptable. High grade 316 stain- Hydronic heating authority metallic hydronic heating pipe are less has proven to be the best long- now finally standard in our industry. term solution. A 316 stainless tank TENS OF MILLIONS of feet of rub- The DIN 4726 German oxygen dif- might be difficult to find even though ber and plastic tubing have been fusion standard was officially in Europe they are readily available. installed in the U.S. and Canada for adopted by the U.S. In- the past 10 years or so to connect stitute as the guide to prevent oxy- For the , it is best to all types of radiation and convec- gen corrosion in plastic systems. use the plate and frame type which tion units back to the . Most of But, remember, this is an endorse- is most economical, compact and it, however, has been used in both ment, not a law. In Europe it’s law! adds little to the pressure drop of residential and commercial radiant the system. floor systems. The unfortunate fact is that now thousands of building owners and After the rubber or plastic system Recently members of the hydronic contractors have to live and deal has been hydraulically isolated from industry have recognized that oxy- with these problem systems for the rest of the system with non-fer- gen diffusion in rubber and plastic years to come. rous components, the second most tubing can cause corrosion in heat- important consideration is to con- ing systems (January 1994, p. 1). My answer is stay away from chemi- vert the system over from intermit- This, unfortunately, was dismissed cals. Use the mechanical method. tent to constant circulation by by leading U.S. pipe manufacturers Even though both methods are means of an outdoor reset control for years as nothing more than un- listed in DIN 4726 as two of three on the primary side of the flat plate. suitable conditions or me- solutions to combat oxygen corro- This can be accomplished via mix- chanical system air leaks. sion caused by diffusion, the me- ing valve or boiler reset. chanical method is the dominant This is not to fault American or Ca- method for old existing non-barrier The reason for this is the lower sys- nadian manufacturers. The Europe- piping systems in Europe. tem water operating temperature ans went through the same learn- and the associated dramatic reduc- ing curve we’re going through now. Grade 316 stainless steel heat ex- tion of the oxygen diffusion rate Once the Europeans recognized the changers are used to separate the through the pipe walls. Constant cir- core of their problem, they reacted mechanical equipment (the boiler culation, however, may not be suit- by introducing barrier pipe and res- side) from the rubber or plastic heat able for all tubing. Check with the cued the radiant floor industry. distribution system, thus dividing the piping manufacturer to see if their system into a primary boiler and tubing is suitable for constant cir- There was a lot at stake. The hy- secondary radiation loop exposed to culation. The potential for prema- dronic market in Europe is about 12 the non-ferrous tubing. ture internal tubing erosion could be times that of the U.S. and Canada. an issue. We also have a lot at stake. Our The system components in the sec- hydronics market is growing, we’re ondary loop exposed to corrosive Before piping up the new system, looking to increase our market share water conditions are the secondary flush the rubber or plastic system and radiant heating is a way to do circulator, the distribution manifold, with water to remove any corrosion it. But we must do it well! the hard piping from the heat ex- sludge in the tubing system and to restore the Btuh output of the tub- ing. Chemical solvents can be used for this only upon consultation with and approval of the pipe manufac- turer.

The initial cost of mechanical sys- tem separation is a relatively high one-time expense but definitely the preferred long term solution to dra- matically extend the usable service life of the system.

The author is president of Stadler Corp. (tel. 781/275-3122), a Bedford, Mass.-based supplier of hydronic heating equipment