hot water heating & dielectric unions

Dan_13

We are installing a large domestic hot water system. A couple of baseboard zones but mostly wirsbo quicktrack under carpet and a large garage with cement floor radiant heat. A cast iron P-WGO-4 boiler and a Ergomax E44 indirect water heater as a tempering tank are in the primary loop. Contractors want to use steel fittings to tie these tanks to the massive copper distribution piping. Contractors say the dielectric unions just become a source of leaks and are not realy necessary. In checking the NALCO water systems failure books I find very real concern for galvanic corrosion where copper steel and cast iron are combined in a water system. Perhaps this trouble does not come about for many years and the contractor is long gone? Or is there realy no concern at all in this type of system? I can not find any reference to this in any of Dan Holohans great books. Maby I did not look in the right place. We want to do the right thing. Should we install dielectric unions or perhaps something else like brass nips? Thanks very much in advance. Dan

hvacfreak

I work on alot of institutional ( schools) sites , and see die-electric nipples ( plastic sleeve inside a galvanized nipple ). Victalic is the brand name. Get the ones rated for high temp , I often find where they use low temp ones in hot water heating and the plastic melts out of them.

Al Learner

dielectric unions-hot water heating systems.

After being a 30 year vet in the boiler trade, I found that dielectric unions allthough specified by most engineers are more of a source of potential leakage than any potential electolysis problem. Dielectric unions are for water temperatures that do not exceed 160* to 180* water temperature. The import ones can't even handle more than 140*. The expansion and contraction of the union due to fluctuating water temperature causes the union nut to move, loosen and leak. Due to the temperature, evaporation takes place at a fast rate and oxidizes on the union threads. Another alternative to the dielectric nipple is to install a brass coupling on the steel nipple, then a copper mip adapter into the brass coupling or fitting. The brass becomes the dielectric break between the copper and steel, the copper mip which will expand faster than the steel or brass will seal further into the fitting and will not leak. If you need to install a union, use a copper union.