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  • OT- Outside Wood Furnace

    I've seen a bunch of these crop up in the last 5 years or so. I am familiar with how a commercial boiler works and is controlled, fired by oil or gas. When there is no demand, they shut off. But with one of these wood burners, it has a fire going all the time and if there is no demand in the house and the circulation pump shuts off, how does the water not boil out of the heat exchange coil? Maybe a bypass of the heat from the firebox?

    They are expensive, and I would have to pipe to a heating coil in the forced air system. Anyone have experience with one?
    Last edited by rws; 12-16-2015, 08:24 AM.

  • #2
    I haven't built one yet,but if heating and hot water costs keep going up I may just do it.I've been watching some on Youtube and most seem to simply control the draft to the combustion chamber.
    I just need one more tool,just one!

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    • #3
      The price of oil is going down but the cost of heating hasn't, think the oil shortage is just as engineered as the diamond market, they just keep screwing us till we sqeal than back off a bit for a while then continue ad nausium as it were.
      Guy in California told me he wasn't allowed to fit a wood burner?, you could only have one if it was always there, don't know if that's true, it's mad enough to sound like local government.
      Mark

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      • #4
        Keep in mind that outdoor boilers are regulated very differently (and a lot less) than indoor wood burning appliances. The consequence of that is my EPA rated wood stove (Blaze King) likely attains 70% efficiency in the real world. Most boilers would be lucky to beat 30%. That also means double or triple the air pollution. Here is a pretty interesting comment from a guy who used to be in the business:

        http://www.woodheat.org/confessions.html

        That doesn't mean you shouldn't do it, but go in with your eyes open.

        Comment


        • #5
          I have one. had it for 8-9 years I guess.
          I like it a lot. mainly because I can beat my garage and shop as well as the house with one fire. bonus is it heats my hot water for the house. my electric bill drops 30 dollars in the winter from that.
          I leave my pumps run 24 hours a day. when house or garage calls for heat it's there as soon as blower kicks on. there is no draft fan on mine but just a dampener door that opens to maintain water temp in boiler. it's a very simple system. jim

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          • #6
            Check your local zoning laws on them. Around here unless you were grandfathered in you need a certain amount of land to own one and there is only certain months out of the year they can be used. They also regulate the "chimney" height. The problem is the smoke that comes off of them.

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            • #7
              They are not hard to build yourself, plans are all over the internet. I was goint to do one as we have steam heat which I love & was told it wouldn't work. My rheary was still use fuel to bring the water temp from almost boiling to boilng. Then I broke my back so it's a moot point.
              "Let me recommend the best medicine in the
              world: a long journey, at a mild season, through a pleasant
              country, in easy stages."
              ~ James Madison

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              • #8
                So, the unit controls the burn to keep from boiling the water? A damper opens and closes, but that isn't very "reactive" so to speak. I'm not sure where I live people get permits or have regulations about them. I see them smoking all year, some closer to a house than others.

                I had an old wood stove in my first house, a cheap one (there when I bought) and it had a bimetalic spring that opened and closed a damper as a heat control. It would build up creosote big time, never would burn clean.

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                • #9
                  If you have a steady supply of wood, than a OWB can make sense, but having to buy wood to feed one can get expensive real quick.
                  Instead of buying an outside wood boiler, look into a wood gasification boiler instead. it burns clean compared to the OWB and you heat up 1000 gallons of water in a storage tank and draw the heat for the house of of that.
                  I have a friend that is running one now and he says he would not switch back to an OWB as his wood consumption is way down. He suggested I look at one to heat both my shop and house when I build my new shop. The largest drawback to them is that they cost more money than an OWB does. But they are allowed in most areas.
                  Dan.

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                  • #10
                    I run a H.S.Tarm boiler in the shop and heat floors in the the shop and house. It is rated to about 80% efficiency. It also has a domestic water circuit separate from the main boiler. I am very happy with it. I do have an endless supply of firewood so it works well for us.

                    Joe

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                    • #11
                      Ironwoodsmith That's the way to go, nothing better than warm floors. If I ever build a house that's what I'll use but with gas becuse my wood cutting days are over.
                      "Let me recommend the best medicine in the
                      world: a long journey, at a mild season, through a pleasant
                      country, in easy stages."
                      ~ James Madison

                      Comment


                      • #12
                        I installed an OWB for a friend about 20 yrs ago when I was a heating contractor. I didn't sell them and didn't want to. I told him to buy the stainless model for about $6,000. I installed the piping in 2 buildings and the indoor heat exchangers. It worked quite well. I don't know if they are still like that, but this one was not a true boiler. It was not pressurized and was rated for a maximum 180 F temp. It was manually filled with water and a bladder kept a slight pressure on it. Firing was controlled by a draft door and if it overheated some of the water boiled off. The owner was to check water level regularly. If the owner was away for a few days, the warm air oil furnace in the house transfered enough heat back into the hydronic circuit to keep the OWB from freezing. The manual said you only had to load it once a day and unseasoned wood was ok. They didn't burn so much as smolder. Imagine a pile of 4' logs taking 24 hrs to burn. So, low chimney and a smoky inefficient fire. I could understand the neighbors getting POed. Insurance companys loved them for getting fire hazzard away from the residence. Russians had the right idea. Heat up a large mass of masonry with a large, very hot, clean fire and then let the masonry heat the home for a day.

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                        • #13
                          The downwind stink of those things is often atrocious. Smells like creosote smoke. Nasty, smells like it should take paint off things. I'd bet most are not as clean burning as a regular woodstove, fireplace or chiminea.

                          There probably are good ones, but even a good one loaded up with wet punky wood is going to stink.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #14
                            Wood gasification is supposed to be as much as 50% to 80% efficient:
                            http://www.greenwoodusa.com/Article_...sification.php

                            It produces a combustible gas that can be used not just for heating, but also to fuel an ICE for mechanical power as well as a generator for electric power.

                            https://en.wikipedia.org/wiki/Wood_gas_generator

                            https://en.wikipedia.org/wiki/Gasification

                            There is a company in Lebanon, PA, that specializes in such products. I may make plans to visit when attending the Cabin Fever Expo in mid-January:
                            http://www.smokelessheat.com/what-is-wood-gasification
                            http://pauleschoen.com/pix/PM08_P76_P54.png

                            Paul: www.peschoen.com
                            P S Technology, Inc. www.pstech-inc.com
                            and Muttley www.muttleydog.com

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                            • #15
                              I use an Ashley wood stove in the shop. A common brand that has been around for a long time. There is a row of fire brick (on end) lining both sides of the burning coals. Besides protecting from burnout I think it keeps the combustion temperature up so it burns cleaner. Outdoor wood boilers do the opposite. The water jacket surrounding the fire never gets above 180 (or 212 in the worst scenario) so the fire never gets hot enough to burn clean, thus the smoke, thus the regulations.

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