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Using wood stove to pre-heat water into a boiler?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Jaugust124, Feb 18, 2011.

  1. Jaugust124

    Jaugust124 Feeling the Heat

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    I'm sure this topic has been covered before, but I can't seem to locate exactly what it is I have been thinking about.

    First of all, I am a completely new wood burner so please excuse my inexperience and I am also not a plumber, so forgive my shortsightedness in that regard as well.

    My insert is located on the first floor directly above my boiler in the basement. I have baseboard heat and there is no hot water storage tank in my system.

    Here's my latest thought. I would have to look closer, but I think that there may be a little room behind my insert. Maybe 6 inches, maybe less.
    I was wondering if there was any way to run a pipe, copper tubing, stainless steel, etc. behind my stove and then have it then run directly down to the basement through the existing masonry floor to the boiler. I have seen devices that are mounted inside the stove and that requires drilling holes in the stove and that does not appeal to me at all.

    I thought that a system such as this would help me to deliver heat to more parts of my home. Obviously by pre-heating the hot water before it gets into the boiler.
    I have been somewhat successful at figuring out how to move the hot air around the house from the insert, but my floor plan is less than ideal. I use numerous fans in doorways and such and it works well, but could be better. I have managed to cut maby 1/4-1/3 off my heating oil bills, but I want to do more and thought this may be a way to accomplish that.

    I am not so concerned about dhw use as its just the wife and I, so we don't run high oil bills in the warmer weather.

    I know there will be some problems to deal with such as overheating the water and needing shut-offs and pressure relief valves and all, but what else?

    Is this even in the realm of possibility or am I dreaming? If this is just a pipe dream please shoot me down so I can move onto some other thoughts.

    Thanks in advance.

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  2. mrkool

    mrkool New Member

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    You said "I was wondering if there was any way to run a pipe, copper tubing, stainless steel, etc.
    behind my stove and then have it then run directly down to the basement through the existing masonry floor to the boiler."

    Ok, I can see a 2 pipes running from behind your stove down to the boiler, supply and return to pre-heat the water.

    Now the question? What do you put behind the stove to collect enough heat to pre-heat the water?

    Well, if I look at my OWB, it has a water jacket all around and on top of the fire, so to get enough heat from using only the back
    of your insert maybe to somehow attach a slab coil/radiator to the back and use board insulation to cover it, that's if the back is totally flat.

    Another option that may or may not work for you could be a copper coil around your flue pipe, I have one wrapped around the flue in my OWB
    that heat my DHW very well, so maybe an option for you to.
  3. Singed Eyebrows

    Singed Eyebrows New Member

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  4. PassionForFire&Water

    PassionForFire&Water Minister of Fire

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  5. PassionForFire&Water

    PassionForFire&Water Minister of Fire

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  6. jebatty

    jebatty Minister of Fire

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    The "hydro-to-heat-converter" is an attractive, although pricey, unit. The wood stove we use to heat our house is more than 20 years old, and consideration of a stove of the "hyrdro" type makes me think of a future new stove as a way to get some heat via hot water into our basement, which right now we have to add some heat with electricity. Will have to keep this in mind and check out stoves of this kind as replacement looms.

    "Efficiency" might be higher than some other quality wood stoves, but like most efficiency ratings, the result is determined by the method used to calculate the efficiency. Using the numbers provided from the link for the B100: high burn input of 133,900 btuh and output of 104,500 btuh from 44.5 lbs. of wood; about 6050 btu/lb for 20% MC wood is pretty standard for heat energy available from wood. The high burn input efficiency is 3010 btu/lb (50%) and high burn output efficiency is 2350 btu/lb (39%). But if output/input is used as the efficiency rating method, then efficiency is 78%, which is what the specs state. I'm guessing, but don't know, that this likely is the method used by wood stove mfr's to calculate efficiency, which doesn't tell the whole story.

    We just dropped into a cold snap, low's right around 0F for the next few days, and I think I'm going to weigh the wood I put into our wood stove and run the numbers like on the site. I'm betting that the "hydro" produces more btu's/lb than my 20 year old stove. The wrinkle will be that I will have to use the btu and efficiency rating on my stove label as the basis for the calculations, and I don't know how either of those were calculated. It will be fun to see the result anyway.
  7. Jaugust124

    Jaugust124 Feeling the Heat

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    mrkool,
    I was under the assumption that since I feel a great deal of heat coming from the front of my stove that a similar amount of heat would be coming out the back of the stove against the masonry wall, The heat is then pushed across the top of my stove by the existing blowers. I sort of just figured that the heat that's being generated would naturally heat up whatever pipes I installed behind the stove without affecting the heat output of the stove that much. Could there be a heat shield behind my stove? Perhaps I need to investigate this further.


    Also, checked the hydro-to-heat website - a bit pricey for me and don;t really have a place to put it.
  8. Dune

    Dune Minister of Fire

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    http://www.hilkoil.com/

    Hi, I know you said you don't want to drill holes, but if you are serious about doing this, check out this site. You only need to drill two holes in your stove. These units are more or less designed to provide DHW, but if you can fit the largest one into your insert, it will heat a lot of your house.

    You said you are not a plumber, that being the case, please realize that without the needed safty devices ( expansion tank, temperature and pressure relief valve,aquastat, dump zone) and proper installation, this could be dangerous. Properly installed it is perfectly safe.

    This is a worthwhile pursuit. Depending upon the size of your home, and the size of your firebox, you could potentialy eliminate the use of fossil fuels. Realize that as your oil or gas use drops, your wood use will increase. I have used no oil at all for the last three years.
  9. steam man

    steam man Minister of Fire

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    I've read this post and think I am missing something. You want to heat your boiler water to take the load off it for heating. What do you typically need for water temp for heating? My point is that I do not see an add on to a wood stove supplying enough btu at the flow rates and temperature you need to make this possible. I have added heat exchangers to a wood stove for DHW to slowly heat the tank without any issue. I just think if its not designed for that heat output your asking for trouble.


    Mike
  10. Duetech

    Duetech Minister of Fire

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    If you know any Amish people you might just find what you are looking for. The Amish heat water with their wood stoves all the time but sinmce most of the Amish do not use elctricity they don't use computers so I don't think you will find a posting. :blank:
  11. Fred61

    Fred61 Minister of Fire

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    In order to preheat water for the boiler with a coil it needs to be able to bring the water up to boiler temperature or at least return temperature in order to be effective, otherwise you will be heating the coil with the boiler. I don't believe you will be able to do either with a coil behind the stove or a hilcoil. You will need to spend several hundred dollars for all the hardware needed to install your preheater and you will be disappointed with the results. Even to get close to the temperatures you need you will need to run your stove flat out. Much hotter than it is designed to run. Don't ask me how I know. It brings back horrible memories!
  12. Jaugust124

    Jaugust124 Feeling the Heat

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    A lot here for me to digest and maybe I'm missing some people's points. I feel like I'm getting mixed messages. Wouldn't any temperature I can raise the water above what its coming in from the outside help with reducing my dependence on oil?
    Boiler temps are set around 180* high and 120* for a low. Temps coming from the stove top run between 400*- 600* regularly with an average of about 450*. So, isn't there similar temperatures coming off the back of the stove? This would not be enough heat to heat the amount of water necessary to feed into my system?

    Again, I am not a plumber and am a newbie wood burner, just spouting off ideas. Perhaps I am oversimplifying what needs to be done, since I really have no idea what I'm talking about.

    Thank you to everyone for the replies. I look forward to more dialogue.
  13. Fred61

    Fred61 Minister of Fire

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    So are you saying you want to preheat your domestic hot water and not the water that is circulating throughout your heating system. If that's the case the answer is yes. water flowing through a coil on your stove would be preheated but it would need to be continually flowing because if it does not move through the coil it will overheat and become steam which could create a mess and possibly cause bodily injury.
  14. mrkool

    mrkool New Member

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    Well, sounds like you've got some brain juices flowing with the idea of preheating your boiler water
    to help save on the fuel usage.

    So, thinking about it again, how about getting a Non-Contact Laser Thermometer from Harbor Freight
    or some other thermometer and take temp readings of places around your stove when hot and then
    you'll know if the back is hot enough to preheat the water.

    But as in my previous post, my Hardy has a water preheat-er, that's a copper coil around the smoke stack
    and I believe that's going to be what you'll end up doing, if you do do it, and that's an option,
    cause that's where the real heat is.
  15. Dune

    Dune Minister of Fire

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    It is not a question of whether it can be done or not, it can. The question is whether it will be effective. That depends upon two things, the heat loss load of your house , and the size of your firebox. If your heat load is low enough in relation the size of your firebox, and the insert radiantly heats a fair portion of the house now, then you could easily set it up to just move some heat more effectively to the rest of the house. The concept of using the wood to preheat the boiler water is not the best approach though. To do that, you would be connecting the insert in series to the existing boiler. Instead, you really want to hook it up in paralell. It is still a very simple system to install. If you are serious, you can get all the help you need here to proceed, at least with the planning stage.
  16. Jaugust124

    Jaugust124 Feeling the Heat

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    Dune.
    I'm not sure what you mean by a parallel system, and the insert does NOT heat as much of the house as I would like, that's kind of what got me thinking about this. There are other alternatives I should probably need to investigate as well, such as new windows and possibly opening up a wall to allow better air flow through the house. I would like to enclose a floor plan, but I am trying to figure out how to do so using Microsoft Word.


    Fred61 - Heating dhw is not a real issue for us, since its just the two of us. Our summertime dhw bills are very reasonable, we average about $50 / month. I can live with that. I
  17. Dune

    Dune Minister of Fire

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    By all means, the first thing you should do is to make the house retain as much heat as possible. I understand from your first post that the heat does not spread through the house as well as you would like. If the insert is capable of meeting the heat load of the entire house, then you could use your existing hydronic system to convey heat created in your insert to the further reaches of your home. The difference between series and parralell is this; in series the heated water would pass from the wood insert through the oil boiler and then through your heat loops. In paralell, it would bypass your oil boiler, run through your heat loops and return to the insert.

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