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Tankless with radiant?

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joshh
joshh Member Posts: 1
in Radiant Heating
I have many customers wanting to use tankless heaters for radiant jobs we are doing. They are mainly in basements and garages. I know I saw an article talking about how they dont work on closed loop systems and how the heat exchanger will only last 3 years. I just cant find the article. Can you tell me why or why not we should use tankless heaters for Closed loop systems?   I am having a hard time switching people to boilers from tankless units, they want to hear more than just "it wont work".Thanks!

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  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,002
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    For one thing

    they don't have outdoor reset controls.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • SWEI
    SWEI Member Posts: 7,356
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    multiple challenges

    Lack of ORC is a big one.



    Warranty issues are practically a deal-killer as very few tankless heaters have an "H" stamp.  Most manufacturers have an outright prohibition on heating use, though Takagi/AO Smith allows it.  Then there are the low flow rates/high head loss.
  • Gordan
    Gordan Member Posts: 891
    edited December 2011
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    That starts to get to the heart of the issue...

    ...which is that water heaters are optimized for relatively low flow rates and high temperature differentials. Their heat exchangers were designed to be efficient in those conditions, but those conditions are not optimal for a lot of radiant systems (those that require lower temperature drops for comfort reasons, which may be the majority of them.)
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