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  1.  
    After burning wood in a multifuel stove for a number of years we have a layer of hard shiny creosote 5mm to 10mm thick in the unlined chimney. A camera shows it extending for 2m to 3m above the sweeping door which is above the mantelpiece, before becoming more patchy. The house is stone, 300 years old. The chimney is not large - estimate 350mm x 250mm at the top, bigger lower down.

    Two sweeps can't make any impression, one with a normal brush, one with a plastic flail. Reaching in through the sweeping door, it's very difficult to remove with a paint scraper, but small pieces can be chipped off by hitting it with a chisel. This is after burning smokeless fuel (virtually no wood) for two winters, and after spraying the bits I can reach with a strong solution of caustic soda (100gm water, 45 gm caustic soda, very nasty, take great care).

    I've read of a product that's claimed to make it friable (Creaway) but can't find anyone who uses it in this area (south Cumbria or north Lancashire).

    We intend to have a liner fitted after the creosote is removed. Please can anyone suggest a course of action?
    • CommentAuthorgyrogear
    • CommentTime7 days ago
     
    I suppose you have already tried one of these ?

    http://www.firewood-for-life.com/chimney-cleaning-logs.html


    gg
  2.  
    Not used chimney cleaning logs, but we tried some chimney cleaning powder on the fire - no effect.
    • CommentAuthorgyrogear
    • CommentTime7 days ago
     
    The benefit of the logs, is they last a long time - maybe an hour, and send the temperature soaring...
    I use one a year (and I sweep my flue 3 x a year...)

    gg
  3.  
    The quickest method I saw a chap use was to set fire to the creosote, although he could totally close off the bottom of the chimney to extinguish the resultant fire. I saw the chimney afterwards and it was without any creosote and the said creosote was reduced to a black powder that fell out of the chimney. This method is not without risk and I would not recommend it - but it did work !!

    Perhaps a bit more realistic approach would be to leave the creosote where it is and put in the liner and then fill the space between the liner and the chimney with non-combustible insulation and ensure a good seal between the liner and the chimney. Or if it is to be a twin wall SS insulated liner then that should be enough on its own (and leave the creosote where it is)
  4.  
    Thank you to both for suggestions (I'd thought of the fire and chickened out). I'm encouraged to try logs for maintenance. The installer pointed out the penalty of a large quantity of dirty wet vermiculite coming out if we ever need to remove the liner (there isn't space for wrapped insulation). I'm continuing to try for a chemical remover for now but not at all confident that it will work.
    • CommentAuthorJonG
    • CommentTime6 days ago
     
    It might be worth checking the size of your stove against your demand, often deposits of this nature suggest an oversized solid fuel appliance, which is failing to reach the really high temperatures required to burn off all the nasties, which then get left as deposits in the chimney or linings of the wood burner.
    • CommentAuthorgyrogear
    • CommentTime6 days ago
     
    <blockquote><cite>Posted By: JonG</cite>failing to reach the really high temperatures required to burn off all the nasties,</blockquote>

    +1

    A flue thermometer being an essential accessory...

    gg
  5.  
    You can also get creosote deposits if the chimney is oversized for the stove, especially with modern stoves that are designed to maximise useful heat and minimise lost heat up the chimney. It could well be that the cause of the creosote build up is that the chimney is oversized and therefore would never get warm enough to stop deposits forming.

    carrotandturnip I don't understand the comments by the installer when they pointed out the penalty of a large quantity of dirty wet vermiculite coming out if we ever need to remove the liner. Does this imply that the liner will not be insulated? Liners work much better when they are insulated and need cleaning much less frequently.

    However I would still suggest, whether or not the liner is insulated, to leave the creosote alone as too much trouble to remove and put in a register plate to close off the gap between the liner and the chimney and a similar closer at the top, but some level of ventilation through the chimney will be needed unless you intend to remove the old chimney down to first floor ceiling level and have new chimney comprising of the liner, (which needs to be insulated above first floor ceiling level) going through the roof.
  6.  
    "[if] the chimney is oversized and therefore would never get warm enough"
    "A flue thermometer being an essential accessory..."

    Interesting idea which I hadn't thought of - I have a thermocouple - but not at least until I've had a go with the chemicals so can make a good blaze. The stuff is being posted today. The stove has a back boiler, which probably cools the flue gases more.

    "Does this imply that the liner will not be insulated?"

    It will be double skinned, but there is a tight point so there's not space for anything larger to be pulled down the chimney.

    The stove is forward of the fireplace, in the room. The new flue will exit the top of the stove and bend to enter the wall above the mantel shelf (so stone shelf needed). The space between the liner and the chimney will be closed at the bottom, and the installer says he will make a ventilation hole in the side of the chimney stack. So there won't be much air to supply a fire between the liner and the chimney.

    I think we will need to roar the fire more frequently to avoid a repetition of the creosote accumulation.
    • CommentAuthorgyrogear
    • CommentTime5 days ago edited
     
    <blockquote><cite>Posted By: carrotandturnip</cite>he installer says he will make a ventilation hole in the side of the chimney stack</blockquote>

    Do you have more details about this -- such as height off floor ? Why is it necessary and what is being ventilated ?

    gg
  7.  
    "Does this imply that the liner will not be insulated?"

    It will be double skinned, but there is a tight point so there's not space for anything larger to be pulled down the chimney.

    Are we getting confused here? All (I think) s/s liners for solid-fuel (not gas) use are twin-walled, but the flexi-ones (liners, as opposed to free-standing s/s chimneys) are not, in my experience anyway, insulated. Therefore you need to add insulation. In my case I have 150mm liners, and due to the vagaries of the flues, I doubt I could have pulled a bigger liner down, but there is room for loose-fill vermiculite.
    • CommentAuthorJonG
    • CommentTime5 days ago
     
    Nick is right most liners are not insulated but some are available with in situ insulation and also a jacket can be added prior to installation, but by far the most common solution is vermiculite or similar poured to fill the voids.

    I would definitely check output to demand though because the flue might not be the whole story here, and if the demand isnt there you will struggle to achieve a stochiometric burn.
  8.  
    I understood the ventilator will be above the roof, to ventilate the space between the liner and the chimney.

    The stove is 1980s. It's a Logfires Gloucester, not made any more I think, and rated 8kW. The flue outlets are for 150mm or 6 inch liner, which is the size of flexible liner proposed. We tested a short length down the chimney, and it needed pulling quite hard in one place.

    The installer says that most of his installations don't have insulation, but I can if I want.

    A few days ago I sprayed the visible part of the chimney with a concentrated sodium hydroxide solution (see original post), and we have lit fires (smokeless fuel) on two evenings since. This afternoon I had a prod at the creosote with a paint scraper. It doesn't seem much different. But I will await the stuff that is being sent and try that.
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