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Woodstove with domestic hot water loop

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by kiwi, Nov 29, 2005.

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  1. kiwi

    kiwi New Member

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    Gidday,

    We are in the process of installing a Domestic Solar Hot Water system. We would also like to supplement the DHW on cloudy cold days with a DHW loop in a free standing woodstove. We have sized the storage tank to accomodate both forms of hot water heating. Now I'm in the process of locating a woodstove with the loop factory installed. I hesitate buying a new stove and then voiding the warranty by drilling holes in the stove to install the loop. Any ideas?

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  2. begreen

    begreen Mooderator Staff Member

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    D'pend what's available to ya mate. Efel makes stoves with a hot water coil.
  3. Sundeep Arole

    Sundeep Arole New Member

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    This has been discussed here before. You can find a article addressing this in the archives. I don't know if there are any stove models currently which offer a hot water coil as a option, although I do recall someone mentioning one. However, if you really want to mostly depend on your solar system + wood, you should consider a TARM boiler. There are multi fuel models which burn oil/gas and wood, and there are wood only models which can add on to a existing oil or gas fired boiler. You can likely share the heat storage tank between the solar system and the TARM, but the TARM needs a big heat storage tank.
  4. webbie

    webbie Seasoned Moderator Staff Member

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    Yeah, I don't think you will find a USA stove with hot water loop available. Nothing wrong with a little drilling - what's going to happen to a stove anyway? (That's my opinion, anyway!)....

    You can use one of the Hilkoils or the Yukon Hot Rod inside the stove, or else a pipe mounted one like:
    http://www.fluemiser.com/

    The pipe mounted one is probably best with a non-cat stove with a relatively high stack temp.
  5. begreen

    begreen Mooderator Staff Member

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    lighten up frank. i take responsibility for my accent.
  6. shredney

    shredney New Member

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    Well I hate to put a damper on this parade, but..... Do Not, drill any holes in the side of your new stove. Not only will you void any warranty you may have paid for, but if anything should go wrong you may void your insurance. I can tell you that a coil inside a woodstove not properly sized can be very dangerous, imagine this scenario. You have a big fire in your stove and are happily circulating water through the stove to your storage tank. Then the power goes out, your circ pump stops and there is still water in the coil. You will very quickly generate steam and steam is explosive. I know someone here will say put a pressure/temperature relief valve in the system. However it is critical to any design to locate that relief exactly right. I can tell you there is a reason why there are no longer any domestic (North American) manufacturers allowing coils or heat exchangers in their stoves today, and it is due to liability. Companies making cookstoves do but the manual for their heat exchanger is double the size of the stove manual, and there are many disclaimers. So don't drill !!! As far as heat recovery devices for the chimney connector or stovepipe go, check with your local fire inspector or dealer, for instance in Canada, these devices are not allowed, whether they are air or water heat recovery units. One reason of course is that with a modern efficient wood stove the flue gases can be relatively cool to begin with, and extracting more heat from it can cause draft and creosote problems, and you don't want any of those. In short, if you want to heat water with wood, please use a unit designed for that purpose, like a boiler. The Tarm is an incredible unit by the way, albeit a bit expensive. Look around for what is in your area. And I too applaud your decision to burn wood. What part of NZ do you live in?

    Good Luck
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    Kiwi,

    You might be better off building a storage tank to store your solar-heated water. I heat my DHW with a boiler, but I'm not sure how well that would work with a wood stove coil. Steve raises some pretty good points about the potential problems. I mean, if the coil were to fail, you'd not only have a flooded house, but probably a ruined wood stove in the bargain. And I wouldn't trust ordinary copper not to fail eventually when subjected to the kind of heat swings the typical firebox generates.

    I think HotFlame's right about the Tarm, but I don't think the (very expensive) water storage tank option is necessary in many applications. It's recommended by the manufacturer, I know, but I've successfully heated homes all winter with much less efficient boilers than the Tarm Solo and with the exception of a 40-gallon hot water heater, never used a heat storage tank.
  8. Rhone

    Rhone Minister of Fire

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    Wish I could copy & paste what I wrote a month or so ago. Here's the scoop.

    25 years ago we got a wood stove with water coils in it. Worked great, except that environment inside a wood stove is so harsh the coils lasted 2 years and they sprung leaks and caused lots of damage and cleanup. When you tried to remove the faulty beasts, it was nearly impossible! Have you ever tried to take a bolt out of your furnace, muffler, etc after its been repeatedly heated & cooled? Practically impossible. We had to cut them out and being heated and cooled frequently the pipes needed to be cut and were like Samurai swords. After that, we put in new ones and had to drill new holes and retap them as the old bolts wouldn't move. Long story short, the pipes lasted a couple years because of the environment, were impossible to get out, new ones nearly impossible to put back in, and this was a stove designed to use them! After several years and a couple replacements they came out and stayed out.

    Why don't todays stoves have water coils in them? Because they suck the heat out of the fire and make it almost impossible to get the high temps needed to get the efficiencies of EPA approved stoves. If you put water coils IN your stove, you'll put yourself in my paragraph above AND your stove will run less efficient, cause creosote to form, you'll need more wood to compensate, etc. etc.

    Then, someone came up with the idea wrap coils from your water tank around the flue of your stove. Well, todays stoves only allow just enough heat to go up your chimney to get proper draft and prevent creosote formation. Wrapping the coils around your stove flue pipe saps the heat out your exhaust and you no longer have enough left for draft, creosote forms, without proper draft your burns are terrible, you smoke the house, and put yourself in a dangerous perdicament.

    I recommend you get an electric heated water tank, they supplement your solar nicely and you don't get standby losses. Almost all solar DHW users have electric backup to their solar for cloudy spells. Good for you though, glad you're doing it. In a few years I plan on doing it. Can I recommend you replace your roof shingles first? Solar panels today usually last around 30 years. You don't want to be putting them on a roof that needs replacing in 5-10 years. If you do come from New Zealand (hence the kiwi) your country came up with the secondary burn technology. The USA & Canada have been tweaking it (our laws are more strict) and using it instead of catalytic converters in stoves). Secondary burn is probably old technology for you.
  9. kiwi

    kiwi New Member

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    Thanks everyone for the great advice. I think we will skip the wood stove water loop and focus our attention on the sloar panels and then space heating with the wood stove.

    Sorry to burst bubbles; I'm a kiwi transplant raised in NZ, but now residing in the US.

    Thanks again, kia kaha.
  10. Corie

    Corie Minister of Fire

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    All of the harman magnafire coal stoves are hot water coil capable :)

    Don't know about the wood stoves though
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