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HDE a? on p/s on navien

jonny88jonny88 Member Posts: 1,139
Hi .I was on a job today and in the boiler room there was a new Navien combi boiler.It was piped like an atmospheric boiler,three pumps on feed and purge tee's on return.There was no primary/secondary loop.Homeowner said he did not have any problems with boiler.What is going to happen to this system or is it going to continue to run without any problems.Thanks for your time.


  • AlexSAlexS Member Posts: 69
    Ive seen it also

    There's a plumber here installing them, same setup.  I asked about it, and his reply was he only installs these now since there's no need for that pesky primary/secondary piping.  I got the impression those boilers arent finicky about flow rates, etc.

    I'd like to hear more about this as well. 
  • HDEHDE Member Posts: 220
    edited February 2013
    Failures coming soon

    I am willing to bet the components or the heat exchangers will not last long.

    I'm sure the first component to fail will be the changeover valve that switches the flow from external heating to internal domestic water production. The valve won't take the excessive pressures when changing while the external pumps dead head against it.

    It too bad it doesn't need a primary loop. Just the system supply going by below while the CH injects heat into system. I have seen these diagrams on naviens site, different than what's in the install manual ( much easier)
  • SWEISWEI Member Posts: 7,356

    in that PDF show closely spaced tees (whenever the LH is not shown) noted as Min 6"

    I'm curious...
  • HDEHDE Member Posts: 220

    Note a boiler with an internal/external pump is not always the primary. Many manufactures inject heat into the system. In that case the system piping is the primary loop and the boiler is the secondary loop, potentially lower in flow than the system heating primary loop. The distance is then there to assure reverse flow doesn't happen having hot water recirculate back up the boiler return reducing DT and driving down output and efficiency.

    Look Weil McLain has done it for years saying 8-12"
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