looking for any feedback on combi  ie Navien ch240 or rinnai combi boiler  have project that one of these would work well,    most combis I find have low dhw output  but it appears that these have higher outputs   need wall mounted unit and would like to avoid tank  ,  have load for house of 55k and another 45k for shops  project is in foothills of cascades in oregon  all concrete construction icf walls and sepended concrete slabs little or no solar gain north side of river gorge

I doubt that many of these Naviens have been installed in the US, but the design looks reasonable- it's a mod-con with an isolating plate type internal heat exchanger for the DHW. The Navien's lowest modulation is ~17KBTU/hr, whereas the Rinnai units bottom out at ~35KBTU/hr, which which may make a difference in as-used efficiency, since the Navien would be able to sustain longer/fewer burns. To keep them from short-cycling into an early grave on hand-washing draws it's probably worth taking the internal mini-tank options if available.

Which to go with should be decided more on support than features though. If the nearest distributor or certified tech is 700miles away from you, it might be better to go with something else.

Rinnai is the worlds largest gas-fired appliance manufacturer, with a good rep. From what I've heard (no direct experience) Navien has had some issues with the quality of installation in N. America (not enough tech-training for plumbers?) but will stand behind the products. According to scuttlebutt (a very reliable source :-) I don't actually remember who told me this ) much of their design talent for tankless HW heaters & condensing boilers came from Takagi (another large Japanese gas-heater manufacturer with a decent track record), unhappy with the company's development direction. (Unlike most vendors, Takagi won't void the warranty of their standard HW heaters in combi or space-heating applications. Rinnai & Navien both allow some of their standard HW heaters to be used as combis, but with restrictions- Rinnai being much pickier than Navien.) I've seen several seemingly reliable installations of HW heaters from both, but have no direct experience with combis from either.

I'm assuming you'd be looking at the propane versions, given the remoteness of the location (in gas-grid terms)?

The combis are a great idea, but support is the key as Dana suggests.

The body of knowledge following smart water heaters is light. The combination boilers have been out for some time with limited success save the Excellence perhaps.

Since plumbers typically receive zero training and the same amount of testing in the realm of gas-fired products, one would do well to find a contractor whom has availed himself the limited factory training available. To my knowledge, Navien has yet to host a service school.

As for misapplying the ubiquitous "tankless" water heater for dual duty, Dana correctly points out a few of the shortcomings but his observation is neither comprehensive or exhaustive.

Dana,

Google badger boiler and send me a regular email for the panel rad info.

thanks for the input I have Naviens HWh installed regularly and both myself and HVAC sub attended Navien training a one day troubleshooting and installation seminar. they just open a full 3 day training this month not sure if we will send someone cross country for this one. Here Navien is distrubed thru HVAC distrutor which I beleive is a better fit. I have both the manufacture' reps and tech support on my phone. We had a period earky last year of getting bad curcuit boards and a sensor that proved fault they paid my tech to change out each unit so have been taken care of.

I ordered their combi unit will let you know how it works out. I will be the first one from my supplier but customer has been prewarned it may be a learning curve for us on this new unit and he is game.