OT: Solar powered electric boiler for home heating

[45K10]

In know this is way OT but since the Paceline is a cornucopia of knowledge I figured I would throw this out there.

We have a NG forced hot water system to heat our home. I like the system and the way it heats but the boiler is 60 years old and even though it runs great and hits only 23PPM CO on a combustion test I think it is time to replace it.

I really want to get a high efficiency condensing boiler like a Bosch greenstar. The quotes for such a system range from $14,000 to $17,000. That got me thinking can I just take that $17,000 and invest in some solar panels, storage battery and an electric boiler and lower my carbon footprint.

As anyone done anything like this? Am I being crazy, should I just stick with a NG boiler and call it good?

Thanks for the help

[cp43]

I'm not sure what you mean exactly by an "electric boiler." We have electric mini-split heat pumps to heat and cool our house. We also have solar panels, but no battery storage for it.

We just had the mini-splits installed this year, so we're going into our first winter with them now. So far, so good, but there is a small concern about how well they'll work in very cold temps (-13F, and below).

We have net metering, so any electricity that we generate and don't use, we sell back to the power company. We generate enough / use little enough, that we don't owe during the summer, when there is lots of sun. We'll see how we do this winter with all the heat being electric. Either way, I think we will save money, since we removed our oil fired boiler. So, no more buying oil.

I never looked into it, but I don't know if anyone makes an electric boiler. I would guess that you'd have to go to forced hot air, instead of forced hot water for your heating.

Chris

[bigbill]

NG is more efficient for boilers. I'm a chief engineer at a factory and we use natural gas for our three boilers. Too many losses and inefficiencies when heating water with electrical. Our system heats up water to 185 degrees and circulates it through heat exchangers in paint curing ovens. The biggest improvement I've been able to make is the addition of new insulation, that reduced my NG bills by almost 15%.

[NHAero]

The answer has multiple levels. Using solar generated electricity to power an electric boiler (plenty exist) is an inefficient use of electricity. Air Source Heat pumps, which use electricity to extract heat from the outdoor air, can deliver 2-3 units of energy for every unit of energy (electricity) the heat pump uses. You have a forced hot water heating system, driven by a boiler that probably delivers the water at 180F, a temperature that currently available air to water heat pumps (such as the Solstice Extreme by SpacePak) cannot match. So your baseboard heaters or radiators won't put out nearly as much heat.

If you put in inverter driven air to air heat pumps, as mentioned above, commonly referred to as minisplits, they deliver the heat via air, so they are not integrated with your existing system. They do provide cooling too, so some folks abandon their existing fossil fuel system and install minisplit heat pumps. Amongst others, Mitsubishi and Fujitsu make units that work at -15F, and lower, without the traditional electric strip heat that American heat pumps use in cold weather. I have buildings heated by these units north of NH's White Mountains.

Solar electricity is a good investment regardless, especially in MA where there is a feed-in tariff program. The Fed tax credit drops from 30 to 26% in 2020, but still it is worthwhile.

My solar electric system is eight years old, runs my all electric house, and powers one car where we live. It's already paid back what we paid for it, too.

[Birddog]

Here is a good site for shopping.
https://www.supplyhouse.com/Heating-Supplies-193000

[45K10]

Thanks for the input!
I am pretty set on continuing to use the forced hot water system for heat and we just replaced the condenser and air handler on our central A/C about a year a go. So I can't see making he move to mini-splits.

I do have a local Solar company coming out to give me a quote for panels next week. Which I still may do even if we stick with NG for heating. It would be nice to run the A/C and the circulating pumps off of solar.

Thanks again.

[AngryScientist]

realistically, if your house is already plumbed for forced hot water heating, you're probably going to want to stick with that method. I think the new very high efficiency gas units will be a big step up for you and the way to go.

taking a look at how efficient the rest of your house is, with regard to insulation and "leaks" is another great opportunity to improve both from an environmental impact and $ standpoint.

[Tandem Rider]

The cheapest way to keep a house warm is to only buy the heat once and never let it escape. That means air sealing and insulation, do that first, always do that first. It's not glamorous to be crawling around in attics, crawlspaces, and basements but it's very effective.

Boiler efficiency, that's a big 'ol can of worms. NG is usually the cheapest way to buy btus, propane, electric and oil generally cost more per btu. If you had a combustion analysis done, they should have given you the firing efficiency as well, this is different than the boiler efficiency, it's probably in the mid 70s for a 60yo cast iron gravity burner.

To get you in the ballpark of ROI, figure out your true gas usage for heat, not for heating water, fireplace, cooking etc, figure out the difference in efficiency, assume the savings based on gas usage, divide into the cost of the boiler. EG, if your annual gas heating cost is $1000, boiler is 20% more efficient, estimated savings is $200 per year, 14,000/200=70 years payback assuming consistent cost of NG (never going to happen).

[rain dogs]

EDIT: Sorry, I misread. What I wrote below was incorrectly reading that you wanted Hot Water not heated water for home heating (ie. radiators, radiant etc.) If you're interested in the Hot water bit, read below, it's still relevant. However, I will preface this all now by saying: Solar, for home heating is best done passively, through building design, as when the sun is providing the most KwH (summer) you don't want much heat (except for water), and when it's providing the least Kwh (winter) you want/need lots of heat. We always want hot water though - for sterilization/washing dishes, and some people always take hot/warm showers. In any event, storing solar in batteries and using that for home heating is extremely inefficient.

You CAN still use this system I described below for home heating but that's kind of a 'bonus' side use. You'll still be relying on your Natural Gas boiler for the majority of your heating needs in winter... you might save 20%??? Maybe? Depends on your Solar region.

If you want efficient, really nice quality home heating, that doesn't come from petroleum and that is renewable maybe look at a pellet stove.

---------------------------- BELOW EDIT - HOT WATER--------------------------------------------------------------------------------------

It would make little sense to convert solar energy (radiation - heat) into electricity and then turn that electricity back into heat, through electirical resistance, in order to get hot water. You get major efficiency losses with each of those 'conversions'. In simple terms.

Solar Domestic Hot Water systems already exist and have so for decades. SDHW systems are the most efficient 'renewable' systems (about 40%) because you don't have these 'conversion' losses. The best PV systems run around 16% efficient.

Better yet, you can continue to use your natural gas system as a backup/supplementary load as it has previously been invested in and built long ago. You can also upgrade your boiler if you wish to condensing, or you could go electric (but, of course not knowing your system details, I would on face value recommend against that because electric is almost always the least efficient option in this domain.)

So, in summary:
1. You're interested in solar (renewable) heat for water (domestic hot water) - heat is what the sun is already providing no conversion needed = Solar Domestic Hot Water Panels (not Photovoltaic panels).
2. In the event of long periods of little/no sun, then you'll want (maybe need) to supplement your hot water so you're not running out of hot water quickly. For that, you have your Natural Gas system.... which you'll reduce the use of by some 65-85% (likely)
3. The remaining questions are system sizing/loads and whether it makes sense to replace your existing boiler and those costs. It may be that just easing the load by 65-85% on your existing boiler is enough.

Hope that helps

[buddybikes]

We had an IBC unit HC 20-125 — 20,000 TO 125,000 BTU/HR - (small house) and total installed price was 8K, know we got a good deal (and he threw in lot of piping as we have 4 zones) another bid was for 10k. Our unit got all kinds of energy rebates, so net cost to us was 6,500.

Shop around, heating people throw all kinds of bids hoping for someone to jump without researching.

[bigbill]

Folks mention solar water heaters, my house in VA Beach had a solar water heater, the couple we bought the house from had five kids so it made sense. It had a glycol circulation system that heated a tank of water to around 105 degrees, so much of the time the electric hot water heater did very little work. It was a very economical house as far as utility bills. Unless there have been some improvements, 105-degree water won't heat a house efficiently, you'd have lukewarm water after a short distance and the heat exchanger efficiency would make that even less effective. You need 180+ degrees leaving the tank. There are so many great options for controlling NG boilers, I have a centrally managed system that is programmed based on the expected load. I can check it on my phone. As I mentioned before, insulate everything, pipe flanges are a huge heat sink, don't let the pipes touch the floor or walls, and use RO water with some kind of descaler. I flush my boiler piping out once a year over Labor Day weekend.

[rain dogs]

Originally Posted by bigbill

Unless there have been some improvements, 105-degree water won't heat a house efficiently, you'd have lukewarm water after a short distance and the heat exchanger efficiency would make that even less effective.

This could have been how your system was setup. You can easily get 120F water from SDHW and I'd say 180F is on the high end for home heating, most can do fine with 160-170 (Most condensing boiler around here are set to 70C or 158F)

Anyway, as I stated, the primary purpose of a SDHW system is your hot water. Home heating is just a plus (when it works with solar gain and heating needs) but in any case, supplementing with gas to add heat from 105 (in your case or higher in my experience) will use much, much less NG than heating the water directly from cold out of the mains at 45-55F

[cp43]

Originally Posted by Tandem Rider

The cheapest way to keep a house warm is to only buy the heat once and never let it escape. That means air sealing and insulation, do that first, always do that first. It's not glamorous to be crawling around in attics, crawlspaces, and basements but it's very effective.

...snip...

I didn't mention it in my first post, but before we got the solar panals, and before we got the mini-splits, we had a lot of work done on insulating our house. New windows, new doors, insulation over the outside of the house, air sealing, spray foam in the attic, etc. That made a huge difference in oil consumption, and comfort in the winter.

We wouldn't have switched to the mini-splits if we hadn't done the insulation work.

Chris

[NHAero]

Well said.
Conservation before systems before renewables.
We didn't turn the heat on until a week ago, thanks to the thermal enclosure work we did when we bought this house.

Originally Posted by cp43

I didn't mention it in my first post, but before we got the solar panals, and before we got the mini-splits, we had a lot of work done on insulating our house. New windows, new doors, insulation over the outside of the house, air sealing, spray foam in the attic, etc. That made a huge difference in oil consumption, and comfort in the winter.

We wouldn't have switched to the mini-splits if we hadn't done the insulation work.

Chris

[45K10]

Our house, is fairly well insulated and most of windows are only 2-3 years old.

I do have a company coming in next week to vac up all the insulation in the attic fill in gaps with foam and then blow in 8" of new insulation. I also get new door jamb seals and prop-a-vents for the soffet vents for only $500 since I did it through Masssave.

That is why I'm starting to look at upgrades for the heating.

Thanks again for all of the input!