Incorporate a wood burning support to my current water system.

Discussion in 'Water Heater Forum, Tanks' started by GG_Mass, Oct 4, 2013.

  1. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Greetings ,all.
    I am starting with a plan to accomplish the above statement. I have an indirect hydronic system currently, with a 40 gallon tank.
    I plan to warm up the house with a wood stove starting this or next winter, placed in the basement, a few feet (7-8) from the Boiler /tank area.
    I'm sure you know by now, there are only a 1000 videos on YouTube showing all kinds of nice tricks, but each setup is good for the respective owner and location.

    One principal that I would like to use is : Water is run through a coiled pipe, and the coil is tightened to the outside of a wood stove. Water running through the coil gain heat, and returning to a tank.
    That, is the only constant I have. I do not know weather the water should be running straight to my current tank after them interfacing with the wood stove, or, should I add a second tank, make the second tank exchange water with the wood stove, and have it's hot water exit connected to the main tank's cold water entry. The number of valves or control units needed for this setup will be determined by a professional.

    This is just a preliminary question, if anyone has some experience or knowledge to share, I thank you in advance.

    P.S
    I acknowledge the fact that professional help may be needed on site, however, I need to have a firm grasp of the plan, for many reasons, budgeting would be a good one to start with. (A wood stove cost is not relevant to this part of the budget).
    Thank you.
  2. Dana

    Dana In the trades

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    Even though that would probably work, the benefit is low and you'd have to convince the inspector that the risk of steam explosion is sufficiently low.

    A HilKoil isn't exactly a code-approved plumbing device in MA even for hydronic heating, would violate the warranty of the woodstove...

    ...but could work if you engineered-up the necessary controls, heat exchangers & pumps.

    For the amount of money you'd spend on a hack of dubious benefit you can probably install a heat pump water heater (the GE Geosprings are about a grand at box stores, and subisidized in some utility areas if you're already heating hot water with electricity) which would pull over half it's heat from the room. If that room is heated by the woodstove, over half the hot water heat is from the woodstove, the rest is from the electricity used by the compressor. In summer it would serve to dehumidify the basement too. It's still drawing heat from the woodstove, just in a less direct (but fire-safe and code-compliant) manner.

    If the hydronic boiler is propane fired even a standard electric tank would cost less to operate at recent years' propane prices. If oil it's comparable in cost. But a heat pump water heater's operating cost is less than half that of a standard electric tank during summer, and during heating season when drawing heat from the room (a bit more than half the total heat going into the water), the cost of the wood-heat fraction is dependent on your cordwood cost & wood stove efficiency.

    BTW: If the basement foundation walls aren't insulated you're going to burn a LOT of wood trying to keep the first floor warm mid-winter. the above grade portion of the foundation wall loses about 10x as much heat per square foot as insulated 2x4 framed walls, and if you have to keep the basement at 80F to keep the first floor at 65-70F it's even lossier due to the higher difference in indoor/outdoor temps. Wood stoves and other point-source heat sources (eg: mini-split heat pumps) work a lot better with higher net-efficiency if located in the space you're trying to heat. In most of MA heating with a better-grade mini-split is cheaper than heating with purchased cord wood in a 75% efficiency stove. If the idea of the woodstove is to cut down on oil or propane heating operating costs, it's worth considering.
    Last edited: Oct 4, 2013
  3. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Dana:
    My water boiler is oil fired.
    I am not going to mount the coil within the stove, it is going to be mounted outside the stove, as shown here : http://www.youtube.com/watch?v=b3i249KtB0o . This , will eliminate the warranty issue.
    Of course, one issue that may tank this idea, is the suffocating state regulations here, being you mentioned that it may only have a chance, I'm not sure if it's good or bad news.
    A heat pump is a valid idea, but is counter what I'm trying to achieve. Doubtless, that if I'm looking for an easy life, I can just change the hot water to all-electric. There is going to be a wood stove, burning wood, in that basement, I want to get more out of it, and if that more also works if/when there's no power, that is very, very welcome.
  4. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Dana:
    Although the installation of the heat-pump within close range to the water heater (not too close), as you mentioned, is an interesting point.
  5. DonL

    DonL Jack of all trades

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    Location:
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    Please post pictures, that would be a nice looking setup.

    If it don't work you can always convert it into a moonshine still. Or make clean burning fuel for your automobile.


    Have Fun.
  6. Dana

    Dana In the trades

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    The pre-fabbed coil used in the video is EXACTLY a HilKoil, and is not MA-approved for either potable or hydronic heat plumbing. You'd have to get an inspector to sign off on a variance to use it (or any similar approach with DIY coils.) Hilkoil does not appear in the listings of manufacturers with approved products- scan through the Hs, you'll see. (Thermo-Bilt isn't listed either.)

    And don't count on exterior mounting to not void the warranty on the stove- far from it! If it's mechanically attached to the stove and pulling heat, it's creating thermal stresses that the stove was not designed for. As long as it's not in direct contact you may have an argument for saving the warranty, but you'd also get much lower heat transfer rates.

    To get the most out of your wood stove, insulate and air seal the house, starting with the basement where the woodstove is installed. There are ways to do this without creating moisture problems, and ways that will turn your basement into a mold-farm, so read up on it first.

    I can heat my house with just the wood stove in the living room comfortably down to about 30F outdoor temps, at which point I have to turn on the hydronic zone to the overglazed & lossy family room on the far end of the house where air convection through open double-doors won't quite keep up with the losses at those temps. If the thing were in the (fully insulated) basement there's no way it would keep up- the basement would be roasting, but the rest of the house would have comfort issues. To get a basement-installed woodstove heat the house reasonably you need to put an open grate directly above the woodstove, and another some distance away, to promote convective air transfer between the basement and the rest of the house.

    You also need to size the woodstove correctly for the actual heat load to be able to run it in it's higher efficiency firing rates. An I=B=R or Manual-J type heat load calc is in order, but you may be able to come up with whole-house number based on oil use measured against heating degree days (or a K-factor stamped on a late-winter oil bill, if you have a regular oil supplier keeping track.)
    Last edited: Oct 4, 2013
  7. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Dana:
    I understand the multitude of considerations one should have to be aware of. However, my inquiry is purely on the technical side of things, please see my initial question.
  8. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    View attachment 21823
    Here are some pictures. with some question as well..
    1- cold water suply,tees off to tank and down, to furnace ?
    2- another tee, left towrds the "Kendey Kinetics heat exchange" , and to the right to the tank.
    Why does it go both ways ?

    20131004_201122.jpg
    20131004_201141.jpg
  9. Dana

    Dana In the trades

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    That's a Energy Kinetics plate type heat exchanger, which isolates the heating system water from the potable water. That only means your indirect water heater tank doesn't have an internal heat exchanger.

    There's no way to get one of this work with convective flow systems like the a Hilkoil- you HAVE to pump both the potable and heater sides for it to work. That's why you have separate pumps- one (apparently mounted on the hot water tank) to run water through the potable side of the heat exchanger the other on the boiler side (mounted near the floor in the picture.) If you want to tap in for a convective flow, you'd have to put it on the potable side, but without a check-valve you'll be heating up the wood stove with the coil whenever the boiler itself is running. But WITH a check valve the convective forces may not be sufficient to open up the check valve enough to be effective, and you'd be at some risk of steam explosion.

    (And please stop calling the boiler a furnace- it just makes things more confusing, eh? ;-) If it contains water that it heats up, it's a boiler. If it's a burner with an exhaust-to-air heat exchanger and an air handler, it's a furnace.)
  10. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    That's funny. I keep correcting people about this mistake as well.. I'm a novice in this field, and learned pretty quick that if it's water being heated and circulated = boiler. Yes, that's well known here. About the rest of your reply, I'll take some time to learn it, and reply.
    Thanks.
  11. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Does that mean, that this : http://energy.gov/energysaver/articles/tankless-coil-and-indirect-water-heaters , does not happen in my case ? meaning, that the heat-exchanger coil which is shown inside that water tank, is actually all done on the outside ? - I would assume that can be quite energy (heat) wasteful, no ?
  12. Dana

    Dana In the trades

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    Yes, the heat exchanger is outside the tank in your case, not an internal coil. Insulating the plate heat exchangerand all of the plumbing loops in/out/around/between the boiler & tank to at least R4-R6 fiberglass would be appropriate. Insulating the hot water distribution and cold-water feeds with R4 closed cell pipe insulation (5/8" wall goods, not the cheap 3/8" goods you get at box stores) would be good too- it's a pretty significant standby loss factor.
  13. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Wow, That's a huge piece of info man.. this entitles you to a six pack of your favorite brew, if humans ever really interact outside the WWW.
    I'll add that to me to do list. Does something the in the grade of Armaflex cut it, or are you pointing to something better ?, I think they also make a 5/8" wall model.
  14. Dana

    Dana In the trades

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    The goods on the boiler loop side of the heat exchangers needs to be rated for 220F or better, since it's possible to run your oil boiler at those temps. The 1" wall fiberglass or 1.5" wall goods used for steam cuts it. (Fiberglass at that density is a bit over R4 @ 1".)

    The insulation on the potable side (or the cold-feeds) is fine with just a 180F rating. It need not be as pliable and expensive as ArmaFlex. The cheap polyethylene stuff from Frost King or ThermaCell is good enough, as long as it's 5/8" or more wall thickness. It's all typically R4+ at 5/8", R5+ at 3/4". Some places will sell the pre-formed bits for ells & tees too. Grainger carries a huge collection online, but most plumbing supply centers catering to the trades will have some selection of the cheap stuff. Pre-split-pre-glued goods are easier for retrofits.
  15. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Cool. Thank you.
    Do you think it's worth a shot to call an HVAC service and try to persuade them into this idea ? or I'd be just asking for a hang up ?
  16. Dana

    Dana In the trades

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    I doubt any competent HVAC contractor would risk their plumbing license on a code-violating hack. You might be able to get an inspector to sign off on the variance if you can give them the analysis from a registered PE that shows it's not really a hazard. You'll spend a lot more on engineering and contractor time than it's worth though, IMHO.

    Think seriously about installing a heat pump water heater and just turning off the oil boiler when not being used for space heating.
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