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Thread: outdoor hydronic boiler pipe question

  1. #1
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    outdoor hydronic boiler pipe question

    hello, im needing to replace an old Laars outdoor hydronic boiler. its currently piped in threaded black iron 2 inch pipe near the boiler. id like to replace the last couple feet of the supply and return with copper as the new boiler hooks up slightly different locations. There's nothing wrong with using copper for outdoor piping is there? seems the black iron would corrode more than anything.... sorry, almost never see outdoor boilers around here..

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    I don't see any reason copper wouldn't be ok. It's the pex you gotta watch out for. And that's because of oxygen.
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

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    that's what i figured. i have a 2 inch pro press, so i want to jujst do a couple feet of new pipe in copper, rather than trying to fit threaded pipe together

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    Yeah, that's no problem....however, be sure to install a dielectric union between the steel and copper. Otherwise the galvanic reaction will eat the copper.

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    I'd insulate the pipe too.
    Chaos equals cash$$$

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    Quote Originally Posted by 71CHOPS View Post
    Yeah, that's no problem....however, be sure to install a dielectric union between the steel and copper. Otherwise the galvanic reaction will eat the copper.
    Brass union or coupling or valve just as good.


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  9. #7
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    Quote Originally Posted by heatingman View Post
    Brass union or coupling or valve just as good.


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    True, and won't leak in 6 months LOL!

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    Thanks everyone, that’s kind of what I figured

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    Quote Originally Posted by 71CHOPS View Post
    Yeah, that's no problem....however, be sure to install a dielectric union between the steel and copper. Otherwise the galvanic reaction will eat the copper.
    Chops, you bring up an interesting question. I have worked for contractors who never had corrosion problems with copper to black iron connections. In the years I worked for 2 companies over 17 years, I never saw any damage of that sort. In fact I never saw a dielectric union used with black iron there. Galvanized iron I have seen corrode but that included zinc in the soup.
    I wondered what constituted a dissimilar metal in this application. Ions can create a difference. I know it's not just a different metal that makes one dissimilar.
    Brass and bronze, I haven't seen problems either. They are both mostly copper. Brass with a bit of zinc and bronze with a bit of zinc and tin. I've seen expansion tanks with brass fittings directly piped to iron. Of all the different types of corrosion, electrolytic (galvanic) seems the least understood.
    I had piped in some balancing valves. Brass to black iron. The engineer wanted me to add dielectric unions. He couldn't point to a reference but I did anyway.

    I guess I'm just wondering if this is just a code thing or is it really a problem. I just haven't seen it.
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    The brass fittings are what stops the corrosion. They aren't dielectric, but brass gets along well with almost any metal, with the exception of aluminum.
    Brass mated to copper is fine. Brass mated to steel is fine. No corrosion due to galvanic action either way.
    But it still passes electricity.....
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

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    I've only seen it twice with copper to steel. That was in older hospitals, with fittings that had been in place for prolly 20-30 years.

    I think there are so many variables, it would be hard to pinpoint why one system does it and one doesn't. It's basically the passage of electricity between materials, so it would have to do with random grounding etc.

    I hate dielectric unions, they always seem to start leaking within a year or so...or they seep very slightly and you end up with a ball of calcium build up.

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    One of the worst jobs I’ve seen was cu tube/cu fin evap coil at a citric acid plant. Cu looked good but fins would slide on the tubes.

    Look up a “dielectric corrosion chart” for compatible metals, great reference.

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    The work I did in the North country was about 40% hydronic. Both resi and commercial and some industrial. Brass wasn't the difference. Copper fittings, like adapters were attached directly to black pipe. I had never seen a dielectric union in any hydronic application. Galvanized pipe and copper for a water heater for instance, always used dielectric unions.
    A difference might be in the practice of always firing up a new boiler to drive off any free oxygen in the water. Warnings of corrosion if not. Black pipe to copper probably doesn't react because the water is flat. The excess free oxygen was vented when heated.

    Maybe the practice of using dielectric's is based on not wanting to take a chance. Fear Factor by contractors. Corrosion is a interesting study. When I was in the aircraft industry there were books written about the different types. Electrolytic is probably most interesting. Especially what constitutes dissimilar. Like a thermocouple that welds two metals at the tip to produce an electrical flow when heated.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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    gal is the key no zinc no current.

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    Is there provisions for "boiler protection"(thermal shock)?

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    Quote Originally Posted by hvacker View Post
    The work I did in the North country was about 40% hydronic. Both resi and commercial and some industrial. Brass wasn't the difference. Copper fittings, like adapters were attached directly to black pipe. I had never seen a dielectric union in any hydronic application. Galvanized pipe and copper for a water heater for instance, always used dielectric unions.
    A difference might be in the practice of always firing up a new boiler to drive off any free oxygen in the water. Warnings of corrosion if not. Black pipe to copper probably doesn't react because the water is flat. The excess free oxygen was vented when heated.

    Maybe the practice of using dielectric's is based on not wanting to take a chance. Fear Factor by contractors. Corrosion is a interesting study. When I was in the aircraft industry there were books written about the different types. Electrolytic is probably most interesting. Especially what constitutes dissimilar. Like a thermocouple that welds two metals at the tip to produce an electrical flow when heated.
    I was always told it was Oxygen related.

    Copper to steel very common in Hydronics, was always taught it was okay because the water essentially becomes deoxygenated.

    Unlike in a domestic or fresh water application.

    But I personally have always used a brass fitting or dielectric union as a go between.


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    Quote Originally Posted by hvacker View Post
    The work I did in the North country was about 40% hydronic. Both resi and commercial and some industrial. Brass wasn't the difference. Copper fittings, like adapters were attached directly to black pipe. I had never seen a dielectric union in any hydronic application. Galvanized pipe and copper for a water heater for instance, always used dielectric unions.
    A difference might be in the practice of always firing up a new boiler to drive off any free oxygen in the water. Warnings of corrosion if not. Black pipe to copper probably doesn't react because the water is flat. The excess free oxygen was vented when heated.

    Maybe the practice of using dielectric's is based on not wanting to take a chance. Fear Factor by contractors. Corrosion is a interesting study. When I was in the aircraft industry there were books written about the different types. Electrolytic is probably most interesting. Especially what constitutes dissimilar. Like a thermocouple that welds two metals at the tip to produce an electrical flow when heated.
    Used to use zinc cromate paint on the undersides of my 4x4s when I lived by the beaches. No rust issues. Epa banned it except for use on airplanes. Used to be able to purchase in any auto paint store.

  20. #18
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    Quote Originally Posted by ehsx View Post
    Used to use zinc cromate paint on the undersides of my 4x4s when I lived by the beaches. No rust issues. Epa banned it except for use on airplanes. Used to be able to purchase in any auto paint store.
    Zinc chromate is used for corrosion types other than electrolytic. Uniform etch and intergranuler (sp) and rust. are three I remember from my time with airplanes. Electrolytic (galvanic) takes two dissimilar metals. One more noble than the other. It happens on it's own but water can speed it up.
    There are lots of different kinds of corrosion. Coils today are corroding where it wasn't a big problem before. Formacary corrosion I'm told.
    Copper vent pipes can get pin holes in horizontal runs from sewer gas A question. Why when one state discovered these pin holes they banned it in favor of ABS. Then it was discovered ABS was a bad deal in a fire so the changed to PVC. But even with pin holes, SF still uses copper DWV.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

  21. #19
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    Quote Originally Posted by heatingman View Post
    I was always told it was Oxygen related.

    Copper to steel very common in Hydronics, was always taught it was okay because the water essentially becomes deoxygenated.

    Unlike in a domestic or fresh water application.

    But I personally have always used a brass fitting or dielectric union as a go between.


    Sent from my iPhone using Tapatalk
    I was taught the same thing. Like the instructions to fire up a new boiler as soon as possible. Like I said I never saw dielectric corrosion on a boiler fitting. There could be a problem if a lot of raw was being added for some reason. Leak or waterlogged tank.
    Still using them can't hurt.

    Cast iron resists corrosion way better than steel. There was at one time a lot of iron close to the surface of the planet. Nothing on the surface because of rust. Magnetite and hematite just below. Meteorites survive better on the surface because they usually contain nickle like some stainless steel does.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

  22. #20
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    outdoor hydronic boiler pipe question

    Quote Originally Posted by hvacker View Post
    I was taught the same thing. Like the instructions to fire up a new boiler as soon as possible. Like I said I never saw dielectric corrosion on a boiler fitting. There could be a problem if a lot of raw was being added for some reason. Leak or waterlogged tank.
    Still using them can't hurt.

    Cast iron resists corrosion way better than steel. There was at one time a lot of iron close to the surface of the planet. Nothing on the surface because of rust. Magnetite and hematite just below. Meteorites survive better on the surface because they usually contain nickle like some stainless steel does.
    Pretty sure it’s the silica content that allows cast to be less rust prone.

    Similar to actual wrought iron that used to be common prior to the advent of mild steel.


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