Hi Dana, I'd like to stick with hydronic heat if I can. So I assume that if I could find just a boiler that could meet the low end I'd be ok. Maybe something like a
Navien NHB 150?
Thanks
Even the NHB 150's minimum modulation is pretty high at 10,000 BTU/hr-in/ 9500 BTU/hr (~2800 watts) out it's minimum fire is still over half your design load, and thus way overkill for your application. (Or did you mean the N
CB 150?) It would still need an indirect water heater to run the domestic hot water end. The NHB-80 would be a better choice with a min-fire output of about 7600 BTU/hr (~2230 watts). The NHB boilers all use moderately high pumping head water-tube heat exchangers and
must be plumbed primary/secondary in most applications.
A low pumping head water tube heat exchanger boiler of similar firing range (eg HTP's
UFT-080) would be much easier to deal with from a system design perspective. (It's also sold as the Westinghouse WBRUNG-080- same boiler under the paint, different marketing & warranty chain. ) That series has the same low-end firing range of the NHB-80, but can almost always be pumped direct, and has a built-in second output port & controls to support an indirect. Unlike the NHB there is some amount of thermal mass in the heat exhanger, making it less prone to short-cycling than the NHB when low thermal mass radiation is used. But you still need to
at least do the napkin math on the radiation. (The more idiot-proof they make something the more creative the idiots become. ) It's fairly DIYable for those capable of both the math & plumbing.
An all electric alternative that works very well in your climate the modulating 2 ton
Chiltrix CX34 reversible air-to-water chiller works pretty well when using low-temp radiation, and can throttle back to about 4-5 kw, and could handle the domestic hot water end too. As with boilers, you may need to add some thermal mass in the form of a buffer tank to keep it from short cycling, depending on your radiation amount & type.
