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Using thermomax for solar water heating

Post in 'The Green Room' started by Beno, Mar 11, 2007.

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  1. Beno

    Beno New Member

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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  3. jjbaer

    jjbaer New Member

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    I think theses systems cost thousands of dollars...payback would seem to be a long time given the fact that I pay about $30/mo on hot water.......
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    The panels run somewhat more than $500 each, but there are tax credits involved, so you can get by for a lot less. In NY, for example, there's a state tax credit that combines with the federal credit for more than 55% of the purchase price. That's a tax credit, not an income deduction.

    I think if you bought good equipment and did the work yourself, you could have a very nice set-up for less than $2,000, net, including hot water storage. With the right setup, you can even get some radiant heat out of the deal.

    Are you heating your water with electric, gas or oil, cast? If electric, what's your rate?
  5. Beno

    Beno New Member

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    I will build a house near Ottawa, Canada. Here there no incentives (yet). Like castiron, I am not sure yet if it's justified to go with a solar water heater. I'd like though to design my new house with this posibility in mind. The plan is (meantime) to heat the water with a Kerr oil boiler. Heating water with electricity will be 40% more expensive, and also ties me up on the grid. I am looking at different solar systems, I wonder if there is a third party review of all these systems.
    Another posibility is to add later a wood boiler, like Tarm (to be used in winter). My understanding is that is not recommended to use a wood stove for domestic water heating.
  6. Eric Johnson

    Eric Johnson Mod Emeritus

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    There are websites devoted to solar that could probably answer all your questions.

    You're right about woodstoves not being used very much for domestic hot water production. Boilers do it better and safer.
  7. cbrodsky

    cbrodsky Member

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    I was leaning towards the vac tubes but was convinced to go to flat panels for a variety of reasons including better efficiency per $ - particularly in a snowy climate where the tubes don't melt snow effectively. Our solar installer has also seen many that have suffered seal failures on 1-2 tubes - at that point, those tubes are so inefficient they make up for the extra cost.

    The most important thing you can do during new construction to help enable any solar system in the future is to install 3/4" copper or PEX tubing with thick pipe insulation around them, ideally not in an exterior wall, and ideally near the roof that would potentially have panels - this will help enable a drainback type design.

    We were lucky enough to have a chase to retrofit the assembly into our house but in most 2-story homes, this is a significant obstacle unless you have a chase or closet you can run them through. You'll also need a conduit to support low voltage wire for a roof temperature sensor. Altogether, a small price to pay up front to enable solar later.

    Also, in a northern climate, I think $2K would be hard to do - I'd plan on closer to $3-4K. This is because you'll either need a drainback system or closed loop glycol system - both of which are isolated from your primary hot water tank, thus introducing a little more complexity.

    We went with a drainback system because it does not require glycol or a thermal dump to prevent overheating that can happen when the panels are constantly filled with fluid. This also makes the system more thermally efficient and easier to maintain. The main drawback is you have to have a higher power circulating pump when the system is making hot water. When the roof is hot, water is pumped up to the panels. When the roof is cold or there is a power failure, the pump stops and all the water drains back to the basement. The solar loop has a smaller 20 gallon tank that sits over the main storage tank and a heat exchanger transfers the heat between the two tanks. You could also install such a system over an existing water heater tank and save quite a bit.

    The combined fed/state tax credits make it a much better economic proposition - otherwise, the ROI is going to be in the mid single digits vs. 10-20%.

    -Colin
  8. Eric Johnson

    Eric Johnson Mod Emeritus

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    Are you saying $3-4K if you do the work yourself and after the tax credits, NYS? That was what my <$2K estimate was based on.
  9. cbrodsky

    cbrodsky Member

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    Sorry, I was talking about before tax credits since most folks don't have the deal we have. In NY state, yes, less than $2K is doable - especially if you tie it into an existing hot water heater. If you want a large 120 gallon solar tank and 3-4 panels, you might push closer to $2500 after rebates.
  10. jjbaer

    jjbaer New Member

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    Hi Eric,

    I heat hot water with Natural gas and my summer bill is under $30. That's pretty cheap to justify shelling out $2,000 for an alternative.....
  11. cbrodsky

    cbrodsky Member

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    As long as natural gas prices are good, it is a harder case for solar in many situations. However, with an oil fired system, esp. a tankless coil, or an electric water heater, the payback works out much better because the energy is more expensive. Many homes do not have natural gas service. We were paying $60-$80 per month to run the boiler all summer and supply our hot water when oil prices were $2.20/gallon.

    That being said, given the very long lifecycle of solar hot water systems, which is easily 25 years, you could still come out ahead over gas. A simple way to look at it - if you have $2000 to spend, you can put it in a CD and earn 5% - that works out to $100 per year. Or, you can put it in a solar hot water system and as even if it only works 6 months per year, you "earn" $180 per year in savings, which works out to 9% annually. In reality, you'll get some extra help year-round to reduce the load on your hot water heater making the return a little bit higher.

    At a $4000 system cost, it'll be a tough case to make compared to natural gas if you are only spending $30. But one other way some folks look at these are as a hedge against inflation. You essentially insulate yourself against all future energy inflation costs. If you believe that energy costs will rise in the long term, even at 3% inflation per year, then in 10 years, your $30 bill becomes a $40 bill, but the solar energy cost never went up. This makes the return on the solar investment better.

    All this being said, it is a no brainer good move for the environment, and if the tax incentives spur larger volumes, costs will come down a bit more making it even easier to justify. Costs won't change dramatically, because the technology is fairly established, mature and straightforward, but it will help a little bit.

    -Colin
  12. Eric Johnson

    Eric Johnson Mod Emeritus

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    I seriously considered putting in a solar water heater but since I heat my water with wood 7 months out of the year, it wouldn't make much sense, other than having another cool thing to fool around with and make me feel good. Both of those are important considerations, but I need the money to buy a new boiler, so that's that. I'm hoping that with a wood gasifier and heat storage tank that I'll be using wood to heat our water most of the year, if not all. Depends on how clean the new boiler burns.
  13. cbrodsky

    cbrodsky Member

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    If I had a TARM boiler or other high efficiency boiler outside the house with a good storage system, I'd do exactly the same thing.

    -Colin
  14. Eric Johnson

    Eric Johnson Mod Emeritus

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    The people I've talked to who have Tarms or Ekos and big storage tanks (800+ gals) say they fire the boiler up once a week for a couple of hours and get enough hot water in the tank to last about a week. Once my 16-year-old daughter goes off to college, we're probably looking at 2 weeks.
  15. Sandor

    Sandor Minister of Fire

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    I see this argument quite often when reading about renewable energy systems.

    What you, or anyone else should consider, is the future price and availability of such energy/fuels.

    This year the Virginia legislator is considering the removal of price caps on electricity rates. Most are saying to expect a 30% increase in rates if such caps are lifted. My mom in Maryland got whacked last year by a 30% increase.

    If we have an above average summer, expect natural gas prices to go up, since most secondary power plants are fired with natural gas to meet a/c demand. Last time I checked, NG is not being replentished as fast as it is being used.

    So, if you are likely to stay put at your current residence for the next 5 years or more, I think an investment in solar water heating would be prudent. Along with efficient windows, extra insulation, etc.

    Be responsbile to the environment, and your family.



    This is my opinion, and it certainly is not humble.
  16. cbrodsky

    cbrodsky Member

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    To echo this point, the installer we worked with does very little work on the scale of our meek 2800 SF house. Most of their projects are on industrial sites or very large estates where the owner views the purchase of an alternative energy system as a hedge contract against energy inflation that locks in prices at a competitive value in today's dollars for the next 25-30 years. These are often very financially sophisticated customers more than they are "green" customers. But it is a tough way to sell to the general public, who likes to just say "what do I save this year?"

    In recent years, energy inflation is rapidly outpacing the consumer price index, and all indications are that this trend will continue unless a significant disruptive innovation is made.

    -Colin
  17. northwinds

    northwinds Minister of Fire

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    Is there a particular product or manufacturer that you recommend based upon your experience? This is something that we're seriously looking at with the design of our new house. I also like the idea of a drainback system.
  18. cbrodsky

    cbrodsky Member

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    I have only had this one system, so I can't comment on subtle manufacturing differences, but the flat plate absorbers are all fairly standardized at this point and have been around over 20 years, and are well proven.

    The panels we have are from: http://www.aetsolar.com/ - this company was recommended based on our installer's experience.

    A lot of good info on their site.

    Rheem is the major supplier of solar storage tanks and they offer them with electric backup elements - basically just like a water heater with an extra heat exchanger port.

    Our controller is made by RESOL - they have a lot of good options.

    And the pumps are TACO circulators - industry standard items just like you have on a baseboard heat system. (slightly different size)

    After that, not much to it!

    I also think a drainback system is ideally compatible with possible wood stove generated hot water in the winter. You could even use the same solar controller if you buy a model that supports more than 1 solar panel sensor - a basic RESOL model will do this. You can lead it to believe your wood stove is a separate solar panel array, and then you have a simple way for the same circulation system to decide when fluid should be sent up to a wood stove heat exchanger. As long as your solar tank is mounted below the stove in a basement, this is an easy way to avoid the challenges associated with a fully pressurized water line going into a stove heat exchanger. That presents a lot more concerns with having a failsafe method of avoiding overheating. I may attempt this in the next year or two using our system.

    -Colin
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