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Thread: Dielectric Union

  1. #1
    DIY Senior Member dlarrivee's Avatar
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    Default Dielectric Union

    Is it a good idea to use dielectric unions on hot water tanks?

    Rather than 1/2" copper FIP adapters?

  2. #2
    Master Plumber Dunbar Plumbing's Avatar
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    I use dielectric unions on all my water heater installs but I insert plastic flanged inserts directly into the union into the dielectric nipple.

    No chance for corrosion to build up and close off the connection at that point.
    Read what the end of this sentence means.

  3. #3
    Plumber Cass's Avatar
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    Where do you get plastic inserts???

    I use copper FIP adapters instead if dialetric couplings...

  4. #4
    Senior Robin Hood Guy Ian Gills's Avatar
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    What happened to just using good quality brass nipples?

    All this dielectric rubbish.

    Brass is best!

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default dielectric

    Di-electric unions are strictly "cosmetic". They look good and make inspectors happy, but do NOTHING to prevent the electrolytic action, since that occurs through the water, just like the anode rod does to prevent corrosion. Most rusty hot water problems are caused by corroded di-electric unions OR dielectric nipples which can have the same problems.

  6. #6
    DIY Senior Member dlarrivee's Avatar
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    Well I could care less if it was dielectric or not, I'd just prefer any type of union, over having a soldered on one side and threaded on the other fitting.

    What is the point of a threaded fitting that can't be threaded off?

  7. #7
    In the Trades Gary Swart's Avatar
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    Default

    I believe local code vary widely on how to make the transition for water heater to supply lines, so you need to check with you local code enforcement. In my area, the common way to make this connection is a brass nipple out of the tank (both hot and cold) Then a short length of flexible copper tubing into a male adapter on the water supply. I know some places require a solid connection, so do check you local regulations.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default heater

    IN any case, a direct connection between the copper and steel of the heater is NOT advisable. That combined with water, (water being the key component), IS the formula for elecltrolysis to occur. A 6" brass nipple is the most effective separator.

  9. #9
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    I've always thought having 2 unions right off the top of the HWT is a bit goofy and is just another spot(s) to leak....

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default heater

    NOt if they are installed properly so they DO NOT leak.

  11. #11
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by hj View Post
    NOt if they are installed properly so they DO NOT leak.
    It's still goofy. There is no need for this. If people do it planning on having to remove the tank I'd ask why they plan on removing the tank. And if they think doing that will make the tank easier to change out in 12 years when it fails they're hoping the new tank is the EXACT same dimensions as the 12 year old model.

    Dialectric unions are much more expensive then a 3/4 cu x 3/4 FIP barstock fitting. If if you have to cut the tank out a few times the extra couplings you might want to account for are still cheaper then 2 dialectric unions.

    Not only that but if you have them on a gas tank they're going to be obstructing the draft hood a little bit.

    It's just my opinion but to me have two unions right on the top of a domestic HWT looks mickey mouse.

  12. #12
    Flipper (house)
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    I have worked in a one inspector town that he wanted me to use flex copper and a brass nipple between flex and solid cooper. He didnít care how I connected the flex copper to the steal tank.

  13. #13
    Master Plumber master plumber mark's Avatar
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    Talking Hj is %100 right....unions suck

    Quote Originally Posted by hj View Post
    IN any case, a direct connection between the copper and steel of the heater is NOT advisable. That combined with water, (water being the key component), IS the formula for elecltrolysis to occur. A 6" brass nipple is the most effective separator.

    http://www.brasscraft.com/Products.aspx?Id=227

    Dialectric unionis are a total joke...they dont do nothing...


    Try out These black brass craft connectors some time

    they are the absolute best way to go
    and I feel that they are have all around better dialectric
    properties and you can certainly knock the job out fast

    I have a bunch out in the field since 98 and
    still chugging along very well ......
    Wont know for another
    good 5 years on how much they actually increase
    the life of the heater... but Iknow they wont clog up on top

    some like the plumbing to look straight and uniform
    and that is the only downside to them....


  14. #14
    In the Trades plumbernj's Avatar
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    Quote Originally Posted by master plumber mark View Post
    [URL]


    Dialectric unionis are a total joke...they dont do nothing...


    Try out These black brass craft connectors some time

    they are the absolute best way to go
    and I feel that they are have all around better dialectric
    properties and you can certainly knock the job out fast
    I use Bradford water heaters with the nipples already in the top of the tank.
    Mark, have you seen these?
    Attached Images Attached Images  

  15. #15
    Moderator & Master Plumber hj's Avatar
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    Default flex

    My experience with stainless steel flex hoses is that they will kink before you can make a tight turn with them. The corrugated copper is MUCH better.

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