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Wood furnace in mild temps?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by rescueram, Dec 6, 2012.

  1. rescueram

    rescueram New Member

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    I am new to this board and I would like some info about using a wood boiler furnace in mild temps say from 30 degrees to 55 degrees. My only experience with wood heat is my father's boiler which is from the late 70's so I'm not sure how technology has evolved. My fathers boiler will not burn properly unless the outside temp is below freezing, and preferably mid 20s or colder. I'm not sure if this is a limitation of the boiler or if there is simply not enough heat demand at warm temps above freezing. Can anybody provide an explanation?

    I'd like to use wood heat for a home that is still in the planning (and $ saving) stage. It would be 2,600sf two stories and mid grade insulation. I want to use wood heat as much as possible. Is there a central boiler system that can operate at wide temp ranges like 0-50 degrees? Should I use a small wood stove for heat when temps are above freezing and a boiler for temps below freezing? It seems inconvenient to use two systems but I'd rather do this that rely on fossil fuels for heat. Any input is appreciated.

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  2. peakbagger

    peakbagger Minister of Fire

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    I expect it may be a draft issue, if the installation has a marginal draft, warm weather could make it a PITA to light off. Unless you have storage, it make a lot of sense to have a small woodstove for shoulder seasons. Unfortunately most wood boilers only burn clean when putting out a lot of heat, depending on the design if you dont need the heat, the damper shuts and starves the fire for air and it turns into a smoke dragon. I beleive many of the new boiler require storage due to this issue.
  3. Gasifier

    Gasifier Minister of Fire

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    For your future system ideas. I use a wood gassification boiler with a buffer tank of 400 gallons. I use it year round. I have burned about 40-50 gallons of oil, I have burned with it for a little over one full year. For your future system I would look into the gassification boilers and have at least a buffer tank. More water storage is ideal, if you can afford it. With buffer tank, or more storage, you can use an indirect hot water tank to heat your domestic hot water (DHW) for everything you need hot water for. Using wood. That is the cat's ass right there.

    For your father's current system. He could add hot water storage in, but it would cost him some money. This would allow him to use it at any temp. Heat tank(s) up and let the heat demand draw from the tanks until it needs to be charged again. Some folks with lots of storage go for days without a fire, depending on heat load at the time.
  4. flyingcow

    flyingcow Minister of Fire

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    I have 820 storage. Learn about thermal storage and I think it's the way you want to go. I burn wood year round. A wheel barrow full of wood gives me close to 5 days of DHW( In the summer) for a family of 5. 3 of which are teenagers. I got to admit, it was odd the first few times starting a fire in the middle of summer, when it's 85f outside. As far as your choice of boilers, there are many really good ones out there. Hang out and learn, ask questions. This site helped a lot. Good group here.
  5. Gasifier

    Gasifier Minister of Fire

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    Hey rescueram. I just got thinking about your thread and thought maybe I would ask how far off this next house of yours will be. I was thinking that if it is a few years off, say two or three, you may want to start gathering your wood now. If you decide to go with a gassification boiler they like dry wood. Best to have it cut, split, and stacked (c/s/s) outside for over one year to give it plenty of time to dry. Two years is even better. Keep asking questions, and research hot water storage. You can add storage fairly cheap if you can do it yourself and can find used propane tanks and have someone fabricate the fittings you need to them.
    flyingcow likes this.
  6. pdf27

    pdf27 Member

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    Might also be worth doing some quick calculations on cost of added insulation versus the cost of a bigger heating system. Depending on the construction method it may actually be cheaper to add insulation and go for a smaller heating system (which will also be easier to deal with in future).

    The only reasons I can think of for your father's boiler working poorly in moderate-warm temperatures are:
    1) Poor draft from the smaller temperature differential. Not a problem for many modern boilers, as they will use an electric blower to control this.
    2) Heat demand being very low compared to the design load. All wood burning appliances have this issue. There are two ways of dealing with this - catalyst type stoves which radically improve the efficiency at low burn rates, or large volumes of heat storage which mean you can have short, fast burns to provide heat for a sustained length of time.

    Personally I'd go for the storage option if you have the space and budget for it - plenty of threads about it on here, often using old propane tanks. It does have the big advantage that in moderate weather (if the store is big enough or your house is well enough insulated) you only need to burn a couple of times a week, as opposed to once or twice a day without storage. Better insulation in this case may well allow you to use a smaller (cheaper) boiler and/or smaller tank, as well as reducing the work you need to do filling the boiler.
  7. maple1

    maple1 Minister of Fire

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    'Not burning properly' - does that mean it spends most of its time idling? (with damper closed?) Or does it mean that with the damper open, it doesn't burn good?

    Boilers can be operated very efficiently year round if they have somewhere to put the heat they're generating. That would mean storage. Depending on the boiler and how much you want to stay on top of it, you might also be able to burn year round without storage (e.g. frequent small fires in a Wood Gun) - but the latent heat might roast you out.

    If you're in the planning stages of a home build, insulation is the one area you want to not skimp on. Save the $ saving for other aspects of your build - things like kitchens & bathrooms can be upgraded later a lot easier than insulation & air sealing of the envelope.
  8. stee6043

    stee6043 Minister of Fire

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    I'd agree with maple1 above. For your dollar there are few places you can make up ROI as quickly as insulation. If you're planning a house you should plan to "super insulate" and never look back. You'll thank yourself many times over the coming years...
  9. Clarkbug

    Clarkbug Minister of Fire

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    I just wanted to echo the thoughts of the other members here.

    Technology and wood burning appliances have come a long way from those of the late 70s. (Woodstoves and Boilers both!). Definitely keep digging around here on Hearth, ask questions, and follow gasifiers idea of getting some wood cut, split, and stacked now. If you burn it, you will be glad you did it now. If you go another route for your house, you can always sell it to folks that dont have dry wood and get some money out of it.

    Also, definitely follow the advice about more insulation now. It makes for a cheaper heating system, and less wood you have to deal with each year.

    Welcome to hearth!
  10. rescueram

    rescueram New Member

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    Wow, lots of great info. I will definitely be putting lots of effort into good insulation for my home. I will also have some water storage for DHW, but I'm not sure how much room I will have. I don't think I could store several hundred gallons, but like I said, I'm still planning.I would prefer to go heavy on insulation so I will need a smaller heating system.


    My fathers system will smoke and not burn properly at warmer temps, especially if there is too much wood in the firebox. Example, the day starts out cold and the furnace is loaded with lots of wood everything is fine. If it suddenly warms into the 30s throughout the day there can be lots of smoke. Probably not enough temperature differential and not enough demand at those temps. In his case, I don't think he will be replacing his system anytime soon, so he can only burn wood when the outside temp is 30 or colder.
  11. flyingcow

    flyingcow Minister of Fire

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    FYI- The 820 gals i have for storage is 7ftx7ftx4ft high.

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