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Thread: Navien Boilers

  1. #14
    Join Date
    Jan 2004
    When connected to 80000 BTUs of baseboard(at 170 average water temp) you'll end up with a 30 degree delta. Only really get about 70,000 out of it since your average will be below 170.
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  2. #15
    Join Date
    Jun 2007
    Minneapolis, MN
    This is correct. Output will vary with design water temperature. We install many, mostly, condensing boilers and a few drive baseboard fin tube, but it is not ideal. Many European condensing boilers will not operate above 167F (75C) so this is not an unusual problem. These units must be sized properly and the water quality must be taken into account on both sides of the system. High performance is never free.

  3. #16
    Join Date
    Jan 2009
    Keokuk, IA
    I think nn reality the 150,175,200k input capacity is related to domestic hot water generation, not heating. I don't think realistically you'll ever get more than 100k out of the unit. However, with a 10:1 turndown, it's like having a 100k wall mount boiler combined with a tankless water heater. The only downside, is that domestic hot water is priority over heating, it's either one or the other and never both together. Since I think it uses 160F water for the P&F heat exchanger. You could reach a 50F delta with a mixed system using radiators or a hydronic air handler combined with radiant floor heat. But still only gets you to around 125k.

    That being said, in order to get full capacity on the hot water side, same problem, the return water needs to get to 105F. With counterflow in the HE, that shouldn't be a problem since incomming water will be no higher than 80F in mid summer. So 100F return temps would probaly be the highest it would see if a 20F approach is possible.

    I know on my NR240-A, I can only reach maximum fire once the incomming water temps dip to about 45F in the Fall with my flow limits from the municipal supply at the street. I think about 7 gpm is all i can get on the supply side to it. I know with water temps running around 38F, cranking open the spigot to the soaking tube and I'm maxed out at 5.5gpm. The internal flow control valve actually pinches back flow once it's reached high fire to maintain setpoint. My wife & I were using differnt showers last night and had it pretty mcuh maxed out too. That's a 2nd reason why I'm looking at adding a CH180 for a last little bit of capacity in mid winter, and to put my cast iron radiators back in service and in the future add radiant floor heat, hydronic air handler or coil, likely with dual fuel, and maybe even a snow melt system whenever we replace the driveway. Never hurts to look at the future. I'd love to go to a Navien class to get some more ins and outs of the unit. I've heard a few rumors about the outdoor reset and it's use with a zone system and a few other things. Also more details on the cascading operation would be nice.

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