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Heating and cooling: New build flu for wood burner.

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    Hi I have just read a very similar thread with regards to log burner flues but I need advice on the best system for new build and I do not want to hijack the other thread. I am fitting a 6kW log burner and need to know about flu installation. What is the best system? build the breast and line it after or can you construct the flu more cheaply or differently as you go? I guess as I still have access then other options will be open to me? Can you use clay or steel tubular lengths and fit as you build? Thanks.
    • CommentAuthortychwarel
    • CommentTimeApr 28th 2010
     
    If you are building a complete flue / chimney stack then use a sectional pumice or clay system such as isokern basically in these systems the liner and outer go up together. for 6kw log burner you would probably require a 150mm internal diameter
    • CommentAuthorowlman
    • CommentTimeApr 28th 2010
     
    The insulated pre-fabricated chimeys like isokern are good if expensive and I always think, correctly or not, that they are ideal partners for timber frame or indeed all timber houses. I guess to many pictures in my brain of Hollywood movies with the old burned out homestead and only the chimney left.
    There are cheaper alternatives, brick or block outer, clay liners, and insulated inbetween. Or alternatively lined with SS and insulated again. If you build from scratch like this you can easily increase the insulation to suit.
    As tychwarel says go for a 6" or 8" liner or clay.
  4.  
    So my chimney breast is built in block then I could fit clay sections as I go? What insulation do I fit in the void between the clay tube and the blocks? Thanks.
    • CommentAuthorfinny
    • CommentTimeApr 28th 2010
     
    Liner section depends on the output of the stove fitted, check with manufacturer to avoid costly mistake!:cry:
    • CommentAuthorCWatters
    • CommentTimeApr 28th 2010 edited
     
    <blockquote><cite>Posted By: gustyturbine</cite>So my chimney breast is built in block then I could fit clay sections as I go? What insulation do I fit in the void between the clay tube and the blocks? Thanks.</blockquote>

    Yes. Our chimney is built that way. Outside is from blocks (bricks above the ridge) around 225mm circular pumice clay liner pipes from the builders merchants. However it might be perhaps worth taking a look at the DM or Scancore single block chimney system here...

    http://www.stovesonline.co.uk/wood_burning_stoves/Pumice-chimney-systems.html

    If necessary Leca can be used as back fill insulation.

    If you use round pumice liners I'm not quite sure how the first liner block is supported. This needs care as its carrying the weight. I think ours was cast into a concrete lintle of some sort. Probably a question for your SE. We had some problems with this lintle expanding and cracking plaster in the room. Perhaps consider plasterboarding the chimney breast rather than wet plastering it ?

    I also had some problems getting a stainless steel funnel that went from 225mm clay to 150mm stove pipe. There are several sources on the internet but the quality was dire. Had to send two back as they were made the wrong size and didn't fit. If you can't find one locally go to www.specflue.com . When you set the lintle height supporting the bottom liner block you need to allow enough room above the stove to hide any such adaptors up behind the mantle piece.

    I read somewhere that _flexible_ stainless steel liners aren't allowed for new chimneys. Has to be rigid?
    • CommentAuthorowlman
    • CommentTimeApr 28th 2010
     
    Gustyturbine; look up, hepworthterracotta.co.uk for clay chimney components, they have all the bits including the starter fireplace sections that CW was referring to, they are readily available from most builders merchants. For most of the logwood room heaters a 6" flue is fine, my 35Kw boiler is only 6". The clay liners are both round or square section. Plenty of choice, personally I'd oversize, -- 8" or 9".
  8.  
    Hi,
    Thanks for the help.
    Owlman- I am looking at 9" but how then do I drop down to my flue size?
    1 Can I build a small steel reinforced concrete lintel with shuttering?
    2 Sit the flue on lintels and fit an adaptor under the clay flue before it gets built.
    3 Let the clay flue sit lower than the supporting lintel set up and hide it behind the lintel holding the breast blocks up?
    I hope you understand what I mean?
    Thanks.
    • CommentAuthorCWatters
    • CommentTimeApr 29th 2010 edited
     
    <blockquote><cite>Posted By: gustyturbine</cite>Hi,
    Thanks for the help.
    Owlman- I am looking at 9" but how then do I drop down to my flue size?</blockquote>

    You can use either:

    a) A stainless steel funnel as I referred to above. They fix to the bottom block using screws and fire cement. See something like product code 130?088 = "clay liner adaptor"..
    http://www.specflue.com/leaflets/specflue_multifuel_fittings_leaflet.pdf
    or
    b) A register plate..
    http://www.specflue.com/leaflets/register_plates.pdf

    I think the funnel is better as any condensate runs back into the fire rather than collecting around the bit of pipe that sticks up through the register plate or leaking past the seal (but perhaps best ask for opinions on this).

    If the chimney can't be swept through the stove you may need to put a door in the stove pipe. See the straight pipes and bends with stainless steel/chrome access doors...
    http://www.specflue.com/leaflets/premier_vitreous_leaflet.pdf

    As for Q1-3.. I think that's exactly what our builder did only we fitted the adaptor afterwards. Just beware that the cast lintel will expand with the heat - hence my comment about cracking plaster previously.
  10.  
    Thanks CWatters.
    So the flue from the burner sticks through the register plate with the 9" flue above it sealed against the plate?
    I assume this is how it would be set up so as you say and condensate could rest on the plate?
    With the funnel system then the condensate would run down the clay linerdown through the funnel (narrow end lowest) into the log burner? Is that right? I guess if the funnel was upside down then the condesate would run and pool inside the clay liner looking for ways to escape:sad:
    If I am correct in my thinking then how do you sweep your flue with the funnel fitted if you do not have an access hatch?:confused:
    Wouldnt your brush need to go through the narrow end of the funnel first?
    • CommentAuthorCWatters
    • CommentTimeApr 29th 2010 edited
     
    Posted By: gustyturbineThanks CWatters.
    So the flue from the burner sticks through the register plate with the 9" flue above it sealed against the plate?
    I assume this is how it would be set up so as you say and condensate could rest on the plate? With the funnel system then the condensate would run down the clay linerdown through the funnel (narrow end lowest) into the log burner? Is that right?


    Yes. The condensat is acidic and over time can corrode the plate. If it's allowed to run back into the fire presumably its re-evaporated and dissapear up the chimney. This is just what I've heard. I'm not a Hetas installer or anything.

    I guess if the funnel was upside down then the condesate would run and pool inside the clay liner looking for ways to escape. If I am correct in my thinking then how do you sweep your flue with the funnel fitted if you do not have an access hatch? Wouldnt your brush need to go through the narrow end of the funnel first?


    Yes but that doesn't seem to be a problem. The brush compresses to go through the 150mm flue and the funnel then expands as it gets to the 225mm liner.

    Typical brush is mostly bristle..
    http://www.hotline-chimneys.co.uk/products.asp?partno=BRSHWHT10
  12.  
    Thanks CWatters. Very usefull advice.
    • CommentAuthorowlman
    • CommentTimeApr 30th 2010
     
    CWs advice is good, but often in these situations its difficult to find off the peg items that "fit" as well as you would like, and you end up trying to make good with fire cement. A register plate is, I think the way to go, and as you're building from scratch it is possible to get a nice neat looking job. Get one fabricated, it's not so onerous or as expensive as you may think. The plate itself could be part of the starter for your clay liners, no?
  14.  
    Owlman- so your advice would be to shutter with say ply then place the register plate on the ply and then construct the lintel inc steel rods above the ply with the first clay liner centrally positioned on the register plate so the lintel will be formed around the first clay liner? Is that your advice as I agree it would look very neat and tidy. So from underneath all you would see eventually is the register plate with the flue going into it? Correct?
    Thanks.
    • CommentAuthorowlman
    • CommentTimeApr 30th 2010
     
    More or less yes. The register plate would, presumably be supported on three sides; left, right, and back by the fireplace brickwork, with, over the top of this, one of the starter fireclay units from the matching clay liner range also resting on and mortared into the brickwork and then onward and upward, insulating as you go. seen fom underneath you are right you would see just a flat steel plate with say a 4", downward hanging, 6"(?) spigot, painted with stove black all ready to accept the SS flue section from the stove. The steel plate wouldn't actually be supporting the full length of the chimney above, the starter unit would be doing that, but it would help and provide the neat look from in the room, and provide the necessary join for the stove pipe. I hope that makes sense, or have I got the design and concept wrong?
  16.  
    Owlman, that makes perfect sense to me. Many thanks for the advice.
    • CommentAuthorowlman
    • CommentTimeMay 1st 2010
     
    If you go down the route of a fabricated register plate, my advice would be to go for a reasonably substantial thickness of steel, not just some lightweight thing.
  18.  
    OK thanks Owlman. What is the general opinion on the liners? I have had a price for clay at £10.98 and concrete at £3.98 each! Am I missing something or are the concrete liners rubbish? I am not using the log burner every day. It will be used for the start of winter and end of winter to try and keep the heating off for longer so if concrete are fine I might be tempted? Thanks again.
    • CommentAuthorowlman
    • CommentTimeMay 1st 2010
     
    I can't see anything wrong with concrete, except I guess the weight, I don't know how high you're going. After all power stations are concrete. I just had a thought about the finished look in the room. Are you going for a simple minimal "hole in the wall" or a more traditional two sides and a mantle shelf?
  20.  
    The breast will be wet plastered 4" solid blocks. The look will be fairly traditional but probably with a fitted fire surround with obviously the upper section being the mantle. I only asked about concrete because one local sales rep said that concrete sections cracked and were absolute rubbish! Being a first build for me I was unsure. The cost of clay is so much more though and I will not use the log burner over the summer much if at all.
    • CommentAuthorowlman
    • CommentTimeMay 2nd 2010 edited
     
    I can't say about the fire resistance of the concrete liners. On my 35Kw wood boiler the temp guage in the boiler flue varies throughout each firing anywhere up to about 300 degrees. I doubt that a 9" flue on a simple room heater would generate more than that, and if, heaven forbid, it did crack you always have the option of dropping a SS liner down. It may be worthwhile researching which company casts the concrete liners and speaking to them, I would. Regarding my musing over your fireplace opening the thought occured that if you were having a register plate fabricated you could have a rectangular box section welded onto the front of the plate to double up as a lintle. Overhang the plate at each side in order to tie into the blockwork and you've just got the one component. While you're at it you could also weld a plasterboard stop bead onto the lintle so you end up with a nice crisp top edge. That gives you the option of having a simple plastered "hole" if you so wish. You can decide on a surround later. Make the opening big enough line it with brick slips or brick and with your wood stove inside the opening would look great. Good luck.
  22.  
    Many thanks Owlman. I will look into it.

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