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Dielectric Unions with and Indirect tank

Newtothis Member Posts: 12
edited October 2014 in Domestic Hot Water
I am installing a Weil Mclain Aqua-Plus 45 Pewter Indirect Water Heater. The tank is stainless steel with built in 3/4" Domestic water female NPT and Boiler hot water 1" female NPT sockets. Two questions:
1) Am I safe using a galvanized water pipe to a dielectric union (this is required by code) to connect the tank to the copper domestic piping? or will there be corrosion between the stainless steel and the galvanized pipe.
2) Do I need a dielectric fitting between the indirect tank and the black iron pipe coming off the boiler?


  • Docfletcher
    Docfletcher Member Posts: 483
    edited October 2014
    As a homeowner I recently installed my indirect. I believe you could use dielectric nipples on the boiler connections. As for the domestic water you can use male dielectric unions.

    After the dielectric nipples you can just use a standard brass/copper union.
  • Newtothis
    Newtothis Member Posts: 12
    But can Galvanized pipe touch stainless steel? Or will this elicit an additional galvanic reaction?
  • Docfletcher
    Docfletcher Member Posts: 483
    edited October 2014
    The galvanic action is usually due to electrical currents generated in the water. Since the dielectric material isolates the metal from the water there should be no currents. Have you asked Weil Mclain for specifics with regard to the install instructions?

    In my opinion you would suffer no adverse effects using dielectric nipples no matter what type of steel they go into. That would be so for male dielectric unions as well.

    After my dielectric nipples I used a brass elbow then a plain copper union, and copper pipe to the boilers black pipe.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,597
    I do not like galvi at all. Use brass nipples and a dielectric union after if you must.

    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SWEI
    SWEI Member Posts: 7,356
    I would question the "code requirement" to install them on the potable water side. Copper and 316 stainless are both on the noble end of the galvanic series and they coexist quite happily with oxygenated water.

    Unless the boiler is an open system (very uncommon for gas and oil-fired boilers, but very common with solid fuels) you do not need dielectric separation on the boiler lines.
  • heathead
    heathead Member Posts: 223
    In looking at htp instruction is says not to use dielectric unions in their stainless steel models. I would think they found out some good reason not to if it's in the manual not to.
  • unclejohn
    unclejohn Member Posts: 1,824
    I would never use a di-union unless it was required by code and then I would **** about it.
  • Docfletcher
    Docfletcher Member Posts: 483
    edited October 2014
    Just for grins I looked at the Weil Mclain Aqua-Plus 45 install manual. It calls out dielectric unions for the domestic water.

    For the boiler water they just show unions without any specification for which type of union.

    Since the coil is stainless steel 304 perhaps stainless nipples would be best for the boiler connections?