Recommendations for Navien NFC-250/200H vs Lockinvar with tank (or tankless)?

[GEWaterSoftenerDude]

Hi,

I wanted to get some input on the best setup for heat/water heat for my house.

I currently have a 5700 sqft house running an old (almost 40 yo) Monitor Products MZ20-40 (I think 142K BTU) boiler for heat that is starting to leak a little bit. I also have a water tank boiler for hot water that is a Weil-McLean Plus 100 Series 2 (2005). Based on age of these things, we figured it may be time for an upgrade. I run 7 air hydronic handlers in the house for zone control (3 of them have A/C), and a driveway heat valve (which bare melts anything... it takes 4 hours to see melting).

My plumber originally said a Lockinvar 229K boiler for the heat (maybe overkill?) and it looks like a great unit. I then also wanted a tankless water heater for the hot water and preferably wanted 2 of them. We looked at Rennai. Rennai came back and said that the gas usage would be too much for all units to run at the same time as when the tankless water units turned on, it would rob the gas from the boiler and it would likely shut down.

My plumber came back and said I should then consider 2 Navien NFC-250/200H combi units to work in tandem for the heat and hot water (no Lockinvar). I have read around on this and the reviews seemed mixed. Anywhere from "its fantastic" to "heat shuts off, cold air blows, and these things don't last long". I wanted tankless because I wanted to lower my maintenance (no flushing needed, etc). I'm on soft water, so I was also hoping that I didnt need to run vinegar through it nearly as often (maybe once every few years). The reason for 2 is one could run some heat while the hot water is going. The BTUs would be close to 400K together, so I can see this working.

My ideal set up was to go with a Lockinvar and 2 tankless water heaters in tandem, most likely Rennai. As explained above, it looks like its a no-go. I could possibly go with a Lockinvar and a single tankless Rennai (RUR199-En), but I really don't know if that can keep the water hot for a shower, dishwasher, and maybe laundry all at once.

I would be interested to get input on the above options, or maybe even options that we haven't thought about for heat/hot water that can get me what I want, which is:

1 - Efficient
2 - Low maintenance
3 - Long lasting
4 - I really don't want a water tank unless its absolutely necessary. I really like tankless.

Side note: I live in Durango, CO where winters can get chilly. 10 degree days do happen.

Thanks in advance.

 

[Fitter30]

And condensing boiler is 95% efficient when return water temp is on or below 130°. Above 86%. Ice melt system isn't made to turn on after theres a few inch of snow. The concreate has alot of mass takes a while to heat up. https://www.mastheating.com
Never want to oversize a heating boiler. Boilers are more efficient the longer they run short cycling doesn't do a boiler any good. Gas sizing without drawing a diagram of the piping system along with pipe sizes , fitting count , meter pressure and volume is a guess over the phone. Any combi water heater has to be sized knowing how many gpm is needed max flow and lowest incoming water temp. If you have spa type shower or garden tub whats the flow rate and anything else running at the same time. Boiler brand isn't as important as the contactor and parts availability. More efficient combi the sharper the service people have to be.

 

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[GEWaterSoftenerDude]

Thanks for the input. Yeah its a 1" gas line and actually talking to Navien, they said don't do it... it won't handle the requirements. My plumber came back and said the best we can do is the 229K Lockinvar with a sidearm, getting rid of the Weil-McLean. I'm guessing it will be better than what I have, at least from a savings perspective.