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Navien and CI radiators

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Bill Julian
Bill Julian Member Posts: 162
in Gas Heating
How does the Navien 240 NCB take to CI radiators? I have a about 5 of them only on first floor.
I know I need the Mag filter. Thanks

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  • psb75
    psb75 Member Posts: 835
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    A bit more information would be required. Any other radiation planned? Total heating load? Other small details?
  • motoguy128
    motoguy128 Member Posts: 393
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    Need a good dirt/air separator to ensure the heat exchanger didn’t get fouled. The mag separator I’m not convinced is that big of a deal. We have several out there on cast iron without issues.  

    A Combi works well with cast iron since it’s a high mass system.  

    The one thing to watch is exhaust temp and flow rates.  A combi must to be piped primary/ secondary  and flow rates managed so return water temp is under 149 for PVC higher if you use a section of polypropylene.  Ideally you use the lowest temp possible.  

    A 240 only puts out around 120k for heating because of fixed max flow rate on the internal pump.  At 120k that’s a 27f delta t.    To get more capacity you need a higher delta T as you can’t increase flow any more. In domestic mode it will be over a 50f delta T at max output.  
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
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    Condensing boilers are designed to be used with low temperature radiation . Radiators fall under that list

    There was an error rendering this rich post.

  • Bill Julian
    Bill Julian Member Posts: 162
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    What kind of cir what I need
  • Bill Julian
    Bill Julian Member Posts: 162
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    The other info is 5 radiators calculating to about 80,000 BTU
    medium size couple smaller ones. First floor only nothing on 2nd.
  • Bill Julian
    Bill Julian Member Posts: 162
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    My supplier says Taco 007 to move the water. He insists it will be fine!
  • PC7060
    PC7060 Member Posts: 1,160
    edited December 2020
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    Are you wed to the Navien? I recently converted a old gravity system to a HTP UFT 80 modcon.  Also piped it for DHW via a indirect tank.  
    The UFT is a low head Fire tube boiler.  I use a Grundfoss Alpha 2 on low constant velocity setting pumping directly through the boiler. GPM ranges from 4-5 when starting and 7-8 at temperature. 
    How much square footage are you heating?  I’ve got 11 rads currently active on three floors and even with very low water temps (105F)  I’ll often get high (delta T 10-12F) return water temperatures.
    Keep in mind the BTU rating of the rads is a function of the water supply temperature and based on the 80k number you must have used 160 or 180F supply temperature in your calculations. 
    I’d think your rads would have a hard time dumping that much heat to maintain return water below condensing temperature. 
    I’ve included the link to my system drawing below. 

  • Bill Julian
    Bill Julian Member Posts: 162
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    Cool thanks!

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