Di-electric unions

If it's a closed system you shouldn't need them if you're just dealing with iron and copper.

K

I avoid them like the plague wherever possible. The only time they are needed is on a system with fresh water in it constantly (think water heater) and when going from one metal to another. Sealed and/or treated heating systems where fresh water is not constantly added to the mix do not need them.

I have never seen one that wasn't leaking, dripping, oozing in some form or another after a year or so.

I have 2 on my dhw coil side and they both leak slowly. also 1 leaked that was on my lpg modcon boiler.
huff

Rick S. said:

So a dhw coil should have a di electric connection?

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Are you talking about a DHW coil with boiler water in it or one that has fresh water going through it? That's what will determine the answer to your question.

I used them isolating both my boiler and the oil fired hwh (summer use) different metals and thinking about any stray electrical current. They are not much money and I was thinking that they are cheap insurance and wouldn't hurt anything. I must have gotten lucky, 4 out of 4 don't leak a drop, but they will now that I've spoke out!

I use them all the time and never have them leak on me, the biggest problem I see people doing is over tightening them.........just a quarter turn or so past hand tight is all they need. I usually put a thin layer of leaklock (a blue pipe dope sold around here) on the gasket surfaces as well.

Mine have been in place for heating seasons, no leaking. After they were in place for awhile, I did snug up the gasket nuts.

They are in the current code for any piping between ferrous and non-ferrous metals, including boilers which went into effect for 2010. Even tho I am required to install them, off the record I will say I have seen MUCH more problems from them, than without them on boilers. They cause severe havoc on mod/cons and the smaller passages in the exchangers. Using a brass union will do the same thing without the leaks and corrosion problems, although code doesn't recognize them as such. I have replaced atleast a dozen sets this season , all of them were 1" or larger and some 90% closed up.

Rick S. said:

I am talking about a dhw coil with soft water going through it for hot water for the tub, dishwasher, sinks. I am not sure why would you run boiler water through a dhw coil?

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Tankless coil immersed in a boiler with domestic water running through it. Yes.
Indirect fired coil running boiler water through it in a tank filled with domestic water supply. No

That clear it up?

I have designed and overseen the installation of many wood gasification boiler systems and use dielectric unions quite often. I have rarely seen them leak and if they do a quick turn of the wrench is all that is needed to stop the leak. These are much less expensive than copper unions and they work very well.