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Navien NFB-175H

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FB
FB Member Posts: 45
A Contractor is recommending a Navien NFB-175H with a turn down ratio of 13.2:1. We've had plenty of heat for DHW (using a SuperStor indirect storage tank), radiators and baseboards from an aging Buderus mod-con with an output of less than 80K. Will the Navien's generous TDR throttle it back enough to avoid short cycling? Seems like overkill. Our house is a small, well insulated single story in the Denver area. Would a Navien NHB110 be a better choice to promote longer cycling, condensing and lower natural gas bills?

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  • dko
    dko Member Posts: 644
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    It's possible tech is avoiding water tube Naviens. Navien fire tubes are top notch, but unfortunately start at 175.

    While it does have a great TDR, I would say it's still grossly oversized and you would be paying quite a premium for no reason.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
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    I’d get a similarly sized 80kbtu replacement, no sense oversizing.
    MikeAmann
  • Teemok
    Teemok Member, Email Confirmation Posts: 570
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    Unused capacity is not necessarily over sized with modcon's. When the boilers minimum firing rate is much larger than the minimum load, that is one way to over size. I like the NFB. The larger heat exchanger running at low firing rate in condensing mode is a good thing. 80K @ 5:1 turn down is a 16K min. 175k @ 13.5:1 turn down is a 12.9K min. The NHB is not better. It's apples to oranges different. On cold starts that NFB will quickly put BTU's into cold mass like a beast and then genitally back off as the return water temp rises. What's bad about that? I have one in a large 1905 radiator craftsman un-insulated house. It works great for the client who valves off 80% of the emitters 80% of the time. When the house is full and the whole system is brought on line it heats up fast. A stable burning large turn down ratio is an attribute of a great modern boiler. It means max. firing rates are not as important as they used to be, given it meets max load.