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Dielectric Unions

Dave_23 Member Posts: 190
I have an older home that is a mix of copper and galvanized piping. I have some upcoming repairs where I'll need to bridge between copper and galvanized. Are dielectric unions necessary or is the issue overblown? What do others do or recommend when connecting copper to steel? Thanks, Dave


  • RJ_4
    RJ_4 Member Posts: 484

    I have used a brass nipple before on smaller pipe
  • Dave_23
    Dave_23 Member Posts: 190
    Contractor estimates PEX vs Cu

    I've progressed a bit on this matter. So far I've solicited quotes from two reputable firms in my area. Company A wants to do the entire job in copper, with dielectric unions at any interface to steel. Company B has proposed a PEX solution. Company B also argues that dielectrics tend to clog over time and prefers brass nipples instead. Company B also touts PEX due cost and ease of installation.

    I have no experience with PEX for hot and cold water supplies.

    Any thoughts one way or the other on PEX vs Cu and on the tendency for dielectric unions to clog over time?
  • SWEI
    SWEI Member Posts: 7,356
    More details

    Copper is better for some things, PEX is better for others.  There are trade-offs which need to be taken into account before an informed decision can be made.

    PEX has the same OD as copper tubing, but a smaller ID.  This means more flow resistance per unit of length, which may or may not be a problem for a retrofit depending on the application (and the specific location in that application.)  OTOH, it can be radius bent around corners (in smaller diameters) which reduces friction and noise.

    If you're hanging the pipe, it needs more frequent support than copper does on cold water, and much more frequent for hot water.  OTOH, PEX loses far less heat to the surrounding air and does not have issues with corrosion (galvanic or otherwise) though some types of fittings can.

    PEX tubing itself is reasonably frost tolerant, but the fittings are not.

    Can you give us some more details about the project? How much pipe are we talking about, what diameter(s) and what flow rates?  What is the surrounding environment like?
  • Dave_23
    Dave_23 Member Posts: 190

    Thanks for the reply. The environment is residential, two story, 2000 sq ft home, built approx 1926. One of the two galv steel risers is leaking. The leaking riser and its associated branches are what I'd like to replace. Basement horizontals already converted to copper. The home originally had Sloan valve toilets, so there is plenty of pressure and flow. The Sloan's are long gone, btw. Pressure is at least 60 PSI, even when everyone in the neighborhood is using water. I have a 1-1/2" copper main into the house. It necks down to 1-1/4" after the meter. Pressure and flow are such that showers, sinks, toilets, and washer can be run simultaneously without any noticeable impact on performance. My goal is to maintain this level of service. Noise is not really an issue. The walls are plaster and tend to lower noise transmission than drywall. Not sure if this is a legit concern, but being an older home, we sometimes have a mouse or two, which our cats eventually catch. However, I wouldn't want a mouse chewing through a piece of plastic PEX. Total run length is probably 150' with a mix of branch and riser, split equally between hot and cold. Much of what will be installed will be buried in the walls when I complete the post-plumbing plaster repairs.
  • SWEI
    SWEI Member Posts: 7,356

    is this a 1-1/4" line with branches?  If so, it was sized for the flush valves and there will be no flow problem replacing it with PEX -- even 1" PEX would work.
  • Dave_23
    Dave_23 Member Posts: 190

    Yes, it's a 1-1/4" riser that was installed decades ago to accommodate the Sloan's. It's the riser that is leaking at one of its joints, midway up one of the walls. Plus the steel throws a lot of rust. It's time for it to go.
  • SWEI
    SWEI Member Posts: 7,356
    edited October 2013

    Start from scratch and look at all the fixtures served by that riser.  You may only need 3/4" today.

    One more thing to consider when replacing metal pipe is that if any of it is used as a grounding electrode, you need to make sure there is proper bonding on both sides (or add an additional electrode.)
  • Dave_23
    Dave_23 Member Posts: 190
    Riser Sizing

    The riser serves the following: First Floor 1/2 bath (toilet and sink); Second Floor Full bath (shower/tub, toilet and sink). Do you think a 3/4 inch riser is sufficient or would 1 inch be more suitable?
  • Weezbo
    Weezbo Member Posts: 6,232
    pipe sized by ...

    fixture units is one thing by code another .

    with your home in renovation you should consider adding in at least one hose bib and an ice maker supply for a modern refrigerator and perhaps change all the stops straight and angle out to new ones . with what you have available you could pipe all of that and still have more than enough using 3/4 " pex tubing and some fancy triple branch T's made of pls at the bathroom location maybe even use carry through multi port t's to pick up the other things i mentioned.

    then if you should decide to sell in the future there would still be 3/4 " available upstairs and down to add new rooms and additional bath rooms,already be up to code , with fixtures found in most new homes. you can somewhat ball park fixture units as 32 fu for 3/4 64 for 1 inch 128 for 1 1/4 and even with the new fixtures and hose bib, you are still safely under that amount.

    on an aside even though you could probably pipe it all in in 1/2 " (which subjectively could out preform the older system ) that wouldn't be quite the ticket . by using an anti scald devise you strech out the time the hot water functions at a preset band width as it were so even though a small 1/2" water maker might be fine for you and your wife , having a 30 gallon super store would be something that would keep up with the modern family even if they added an additional bath.

    if your meter is inside your home having it reduced to 3/4 and installing lead free parts and pieces would likely save some $ and be a reasonably prudent investment. 1 1/4 meters or worse yet 1 1/2" cost more to own around here at least...

    new standard industry tub and shower valves and vanities and kitchen sink from moen would also be the ticket for a renovation , that way you can reduce costly repairs down the road, the cartridge is about the only thing that would need to be replaced rather than a variety of different parts and pieces that might be becoming hard to acquire for some of the more vintage valves.

    by upgrading your drain waste and vennt to abs and proper sized pipinng and new fittings and vents your drainage system would also be bumped up a notch to these newer codes. most likely you will have 1 1/2 kitchen and bath drainage , well , these days we use 2 " and with abs being "slipperyier " :) the water rolls along and out the building with very little chance of needing to snake the lines or fittings corroding through at the threaded fittings , old brass trip waste and over flows were nice and all however the new push pulls or toe tappers are way more reliable and once the abs is piped there is little to zero that can go wrong , that a homeowner cannot fix .

    some old fixtures have a lot of sentimental value however plain jane vanilla white would work on the thrones and vanities . you might consider 1 piece fiberglass tub and shower or even an upgrade to the tub by going with 6 foot tub with grab bars etc the thing about plumbing is,... when the walls and floors are open , that's the time to get it done.

    our new quarter turn angle stops and straight stops and frost free hose bibs, really are easier to open and shut .

    well, sorry i expanded out there a ways on your question , buh i hope it helps .


    *~//: )
  • die electric

    Hate those die electric unions, they have no place in plumbing or heating system... also those qtr turn shut offs are the worst kind for older home that have glav and copper mixed. Best and practical safety tub/ shower valve are Moentrol.
  • die electric

    Hate those die electric unions, they have no place in plumbing or heating system... also those qtr turn shut offs are the worst kind for older home that have glav and copper mixed. Best and practical safety tub/ shower valve are Moentrol.
  • die electric

    Hate those die electric unions, they have no place in plumbing or heating system... also those qtr turn shut offs are the worst kind for older home that have glav and copper mixed. Best and practical safety tub/ shower valve are Moentrol.
  • Weezbo
    Weezbo Member Posts: 6,232
    i just realized

    i basically said ,

    i would rather re-plumb the entire house ...lol

    so apparently die lectric unions are not my favorite.
  • Talldutch
    Talldutch Member Posts: 4
    Dielecric unions

    Anytime 2 disimilar(spelling)  metals are joined an approved adapter ftg shall be used  Dielectric union or dielectric coupling  brass nipple or ball valve or gate valve will work  Never join copper to galvinized without any of the above  the 2 differant metals do not like each other and you will have a problem    Hope this helps Marty the Plumber
  • icesailor
    icesailor Member Posts: 7,265

    The codes all say to use Dialectic Unions on dissimilar metals. That said, in over 50 years I never used one intentionally. The ones I found installed on water heaters were usually leaking and the tank was also leaking. The unions were usually leaking on the gasket or ones installed outside on LP gas lines usually had rotted union nuts.

    But the "code" requires them so I guess that makes me an Outlaw. And the inspectors never made us install them. They were always plumbers too. Perhaps their experience was similar to mine. And our local supply houses never carried them. Special order if you want them.
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