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Solar + radiant hydronic baseboard heat (gas powered)

strago13

Member
Feb 9, 2018
139
601
Washington dc
Hi,

I have a unique situation here and I am looking for some practical advice on how to proceed. We have a ~2000 sqft house spread over a 4 level split style with 2 heating zones, radiant hydronic baseboard heat, and a separate forced air AC unit. We also have Tesla Solar (17kwh system) and 3 batteries. The natural gas powered boiler for our heating system is old (~1980's) and likely very inefficient. One way or another, it's going to be replaced in the next year or two. I believe it is a 100k BTU unit. Originally our house (built in 1958) had no insulation at all. We have since insulated the entire place so we're much more energy efficent than when we purchased the place.

I was looking for some input on how I could leverage my likely solar surplus (we just got solar installed in Sept of last year, so I don't have a years worth of numbers yet). So far this year, we've produced equal to what we've used. Over the summer, I expect to 1.5-2x what we use.

Does anyone have any recommendations on electric boilers? Or hot water heaters that could be used to power my heating system? I have found this manufacturer (Electro-Boiler Midsize "MX" Series) out of Minnesota. I spoke with them on the phone and they seemed to indicate I could make EB-MX-17 work but doing rough back of the envelope math seems to indicate not? We live in Maryland.

Thanks in advance for your thoughts
 

zƬesla

Member
Apr 16, 2020
328
99
US-NH
I'm in a similar situation just with an oil boiler instead of gas. We installed heatpump mini-splits for A/C a few years back and used them for winter heating this winter after installing PV last Spring. They are efficient but we are often near 0°F over winter, so the oil boiler did get some use (though our oil bill was considerably lower). I was considering some of the all electric solutions for replacing the 30+ year boiler but am actually now leaning towards simply replacing it with a newer more efficient unit for the main reason that winter PV generation won't likely power the house with an electric heating solution. The mini-splits, when it's really cold, are typically running 3-4.5kW whereas the oil boiler uses less than 0.5kW, so we'd be able to run much longer on batteries during an extended outage.

I realize this doesn't answer your question. There has been some talk in the forums about the Rheem Hybrids, however I don't know if they only handle potable or if they can also interconnect with hydronic heating.
 

strago13

Member
Feb 9, 2018
139
601
Washington dc
I'm in a similar situation just with an oil boiler instead of gas. We installed heatpump mini-splits for A/C a few years back and used them for winter heating this winter after installing PV last Spring. They are efficient but we are often near 0°F over winter, so the oil boiler did get some use (though our oil bill was considerably lower). I was considering some of the all electric solutions for replacing the 30+ year boiler but am actually now leaning towards simply replacing it with a newer more efficient unit for the main reason that winter PV generation won't likely power the house with an electric heating solution. The mini-splits, when it's really cold, are typically running 3-4.5kW whereas the oil boiler uses less than 0.5kW, so we'd be able to run much longer on batteries during an extended outage.

I realize this doesn't answer your question. There has been some talk in the forums about the Rheem Hybrids, however I don't know if they only handle potable or if they can also interconnect with hydronic heating.

Thanks for your thoughts on this!

In MD our utility provider allows us to get a credit for surplus electricity. Do you have something similar in NH? I wish they would allow us to apply that credit to gas, but they do not. The other thing is that we pay less for electricity (8c a k/w ) than we do a for a therm of gas.

I have seen a few youtube videos where people will use a efficent hot water heater as a "boiler" but it requires cranking it up to ~140 degrees otherwise it wont heat the house properly. I think it varies state by state on plumbing code whether or not you're allowed to do this.
 

zƬesla

Member
Apr 16, 2020
328
99
US-NH
NH has net metering but not 1:1 and it's tracked separately. So we get a partial credit for everything we export, and pay regular rates for everything we import. The electric utility is also independent from the oil/gas delivery businesses – we're in a rural area. We had put in an indirect electric potable hot water storage tank some time ago along with something like a cold start so the boiler is not running all the time having to keep the 140°F(?). The nice thing too is the residual boiler heat warms up the basement where we have a craft/play area.
 

wwhitney

Member
Nov 2, 2017
766
924
Berkeley, CA

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