Woodburner Disappointment - Poor Output

Discussion in 'Plumbing and Central Heating' started by subzero, 10 Dec 2010.

  1. subzero

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    Hi

    Can't find a 'woodburner' forum so putting this in plumbing / central heating.

    We just had a 4kw stove installed into an average sized room, 12ft by 14ft approx. It does heat up but I guess we were expecting a reasonable amount of heat from it - enough to heat the room at least, but you can only feel the warmth by sitting right in front of it.

    Bought the stove after doing research and understanding that the 4kw output should be ample for the room size. Logs burn as they should and good draw on the flue etc.

    Does anyone have any advice on this?
     
  2. Richard C

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    Poor performance can be due to a number of reasons including poor stove efficiency, incorrect installation or, potentially far more dangerous, incorrectly sized/blocked flue leading to insufficient draw Was it a registered HETAS install or did you DIY & notify?

    4kw should be more than enough for a room that size, if you have standard height ceilings. I have a 4m x 6m room with an 8kw multi-fuel inset stove. It’s very efficient & more than enough for the room. It will heat the whole house if I stoke it up, allowing us to turn off our oil fired C/H system but the downside is you can’t really sit in the room if you run it at full tilt for long, it gets too hot in there!

    What sort of room/property is it old/new? DG fitted? solid/cavity walls? What type of main heating system do you have?
     
  3. Agile

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    I am always suspicious of the claims for wood stoves. My friend in France has a large room about 5m x 8m and the original stove was meant to give out about 7kW but I changed it for a smaller one which was far better as it gave less to the heating circuit and more to the room.

    Its possible that whilst 4 kW would be adequate in your case that as it takes its combustion air from the room that its just drawing all the heated air up the flue to be replaced by cold air from the outside.

    Tony
     
  4. big-all

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    what you need to remember thats the output with the stove full off the best fuel for about 10 mins off every hour
    you need to top it up every 15 mins to get around 80% max iff you go for every half hour your down to perhaps 60%

    then iff you choose soft wood that burns quicker but cooler you probably down to 40% stoking every 30 mins

    and of course if you get a duel fuel and burn softwood the output drops even more :oops: :cry:
     
  5. RigidRaider

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    We have two identical Dovre 500s in identical rooms with identical flues and ventilation yet the one in the back room sucks like a good 'un and burns hot and clean while the one in the front room is sluggish, smokey and smelly, especially when it's not burning as drafts come down the flue.

    I think I even posted a Q on here last year asking if anybody had any suggestions as to the reason. I believe it might be to do with the prevailing wind and the air flow over the roof. One thing is for sure; even the better stove is slow to light after a few days not lit because the whole flue and chimney cool down and it doesn't begin to draw and light easily until it's been burning for an evening or two.

    Is your wood properly seasoned? If it's not, it will steam and the steam will be cooling your combustion down and damaging your flue by forming suplhuric acid. If you can hear hissing when you burn wood, it's too wet.

    The other issue is the way you burn the wood. One or two big logs will smoulder at the edges but won't give out much heat. A woodburner needs a good bed of glowing embers radiating heat before it will get up to a good temperature and you are achieving proper, hot, clean combustion. You need to create this bed of hot embers by splitting the wood into smaller pieces or by starting the evening with a good layer of smokeless nuggets, which will raise the combustion temperature enough to deal with the big cold lumps of wood you throw in. Wood is a poor conductor of heat and you have to supply a lot of heat to a big fat cold log, especially a dense wood like beech or oak or ash before it will begin to burn. Once a heavy wood begins to burn it will liberate heat for much longer than a light wood like pine, which burns up in half an hour. I can't over-stress the importance of creating a bed of glowing embers; the radiant heat is what warms your room, not a couple of logs struggling in a cold draft from the bottom vent and sending everything up the chimney.

    One word on stove size: the best advice we had when we bought ours was to err on the smaller size because that would mean we would be burning them harder with more oxygen and thus higher combustion temperatures, meaning less soot and less moisture in the flue. So often you see oversized stoves turned down too low with the window all sooted up because the combustion temp is too low and the fuel is smoking.
     
  6. subzero

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    So many awesome replies! Thanks to all

    More info -
    DG installed
    CH installed
    Solid brick 1930s semi-detached
    The stove was installed and commissioned by a hetas engineer.

    The main reason for installing the burner is the potential heat output so we don't have to rely on CH so much. And also for the lovely wood burning smell.

    So far, not that impressed.

    We have a Morso squirrel waiting to be plumbed into the front room, maybe that will do the business...
     
  7. RigidRaider

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    You won't get much wood burning smell if the flue is doing its job; you'd be amazed at how much air gets sucked out of the room by a stove. Sometimes we burn peat that we bring back from Scotland but we have to go outside to smell it properly.

    Keep at it; it takes time to learn how to get the best out of a stove. Once you've nailed it you will love the silky warmth, the atmosphere and above all the dry, well ventilated feel it gives the room.

    We have vents in the same wall as the stoves about 6' away in the corner of the room. That way fresh air comes in and across to replace what the stove sends up the flue but we don't get a draft coming under the door or through the window freezing us. Proper and comfortable ventilation for a stove is quite a subject and needs to be got right; you are creating low pressure in the room and need to be in control of the air that comes in to fill the vacuum.
     
  8. Richard C

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    You are only at 4kw so a fixed ventilator not mandatory (5kw +) but it might be an idea to have one fitted. Solid external walls might be a factor; they tend to be cold (& sometimes even damp) if they haven’t been upgraded with additional internal insulation, especially North facing.

    Otherwise, very difficult to pinpoint what may be wrong (if anything) without seeing/trying it, have you tried contacting your HETAS installer for advise? A stove is not a complicated beast but running a good fire does require a little understanding & experience to get the best out of it without wildly fluctuating temperatures. After 2 years my wife still can’t manage it & apart from chucking on the odd log or few lumps of coal after some prompting, it tends to be left to me. As has already been said, burning logs requires a good ash bed so it will take an hour or so to get going & you mustn’t keep raking it.
    What make/model is the stove?
     
  9. hi1

    hi1

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    i have seen stoves with a vent connected and integral to the fire to supply combustion air. This is taken through the wall to the outside so the fire doesn't draw air from the room, or at least not as much, for combustion doing away with the draughts and change of room air which lead to lower room temperatures. These are usually the more expensive fires.
     
  10. iep

    iep

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    We have an Aga Litle Wenlcok which (I think) is about 4.5kW. We manage to heat a large room (8mx4mx2.7m) using this stove alone.

    However, when first installed I did not do a good enough job of sealing the register plate and we got much less air flow through the stove and the heat output was far lower. With a bit of care I managed a much better seal and now almost all the air that flows up the chimney has to flow through the stove. The result is that it now runs beautifully on smokeless fuel or wood and has kept the room above 20 degrees even when it was below -15 outside.

    Our house has single glazing, a woof panneled ceiling (through which air passes freely) and the room in quesiton has 3 outside walls so I'm sure your're room should be heatable with a 4kW stove.

    Check the seal on your chimney and keep at it, they do work.

    iep
     
  11. Burnerman

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    I think the last post was very important - without a register plate loads of air and most of the heat goes sraight up the lum.
    With a register plate the burner is allowed to radiate heat into the room, and all the combustion air passes through the burner.
    Likewise, the top baffle has to be in place, within the burner casing.
    John :)
     
  12. tryitandsee

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    I installed a morso squirrel heat into a chimney breast opening, it's not so much the heat coming from the stove that is impressive (quite disappointing in fact), it's the heat radiating from the surrounding brick/plaster walls that house it. The walls take quite a time to 'dry out' around the stove, but now after a good fire, the walls start to get quite hot. This heat then carries on up the breast above the stove and around the cheeks to the side. In the end it's the radiant heat coming from the walls that make it warm and cosy, not the stove its self.
     
  13. Corgigrouch

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    You have lit it.... Haven't you?

    Well it is silly season and we all get mad phone calls this time of year.... :p
     
  14. Richard C

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    [​IMG]
     
  15. rayburner

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    You could always try throwing some chipboard and 4x2 offcuts in there -that stuff certainly puts out some quick intense heat
     

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