Sticky, black liquid in woodburners

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Have you found a sticky, black liquid in your wood-burning stove? Perhaps the consistency reminds of tar, and that’s because that is exactly what it is.

You might spotted it running down the inside walls of your appliance or settled somewhere in the firebox.

If you have seen this black liquid, it indicates that you are not operating your stove correctly and, in particular, burning unsuitable fuel.

Usually tar is created as a byproduct of burning logs on a woodburner when the moisture level of the wood is too high. Since energy is being wasted evaporating water, the stove doesn’t get up to high enough temperature, which leads to cooler gases going up your chimney. Since they are cooler, they are prone to condense when they touch the metal of the flue liner.

The condensed gases will either solidify on the inside or the flue or drip back down into the stove in the form of the sticky liquid. Whenever the tar does get the chance to solidify it will turn into creosote. A build-up of creosote in your stove system increases the risk of chimney fires.

How to stop a sticky, black liquid appearing in your woodburner

There are a few ways to stop the black liquid appearing in your wood-burning stove. The first is to ensure that the only logs you burn are ones that have been correctly seasoned and have low moisture content.

Ensuring there is a strong draw up your chimney, operating your stove at full capacity and ensuring your room is well ventilated will also minimise the chance of flue gases condensing in your chimney.

It is also important to get your chimney swept regularly. This will remove any residual creosote that has built up in your chimney and prevent is seeping back down your chimney and into the stove.

Click here to read more about tar condensation.

15 thoughts on “Sticky, black liquid in woodburners

  1. Hi there,
    on a completeley unrelated point, do you know the make and model of the stove in this picture? I’ve got one exactly the same, but the grate is shot to pieces. I’ve no idea of the make and model to get a replacement either.
    Many thanks

  2. My neighbour kindly gives me off cuts from making bird tables for our local hospice shop. This is new wood from the local timber yard and looks to me completely untreated. I am using these off cuts as kindling wood but recently the flu has become blocked with crystallized soot and last night some black sticky goo was dripping down. Could this new wood be causing the problem and what should I do to prevent it happening?

    • Hi Trish,

      If it’s a new problem since you’ve started using these off-cuts, the best advice would be to stop using them (at least until you’ve found out for certain whether they are treated). Have the logs you’ve been burning all been well seasoned?

      Thanks,

      Gr8Fires

  3. Hi, we’ve just removed our log burner and have found a black sticky substance dripping onto our hearth. Seems to do it more when it rains, however
    Ver, we have had fitted a chimney cowl that is supposed to stop rain coming down the chimney liner. Any one got any thoughts please?

    • Hi Tony

      It’s likely to be creosote deposits in the flue being washed down by the rain. Try burning only well-seasoned wood or getting the chimney swept.

      Thanks,

      Gr8Fires

  4. Hi we have just had a liner fitted and swept. After a month of use we have had a deposit of black sticky gloop. Another piece was like a black piece of crystallised tar. Is this normal?

    • Hi Sherie

      This is creosote, which would suggest that one of the following his happening:

      – The wood you’re burning is too damp.
      – You’re overfiring the stove (allowing too much air in when it’s in use)
      – The draw up the flue isn’t strong enough (flue gases are condensing and solidifying into creosote inside the flue)

      Thanks,

      Gr8Fires

  5. Hi I have a multi fuel type stove with a backburner and its large , it’s started to drip the tar like substance down the outside of the flue out of the chimney ,but I haven’t lit the fire since April and its now September, I also have a rain cowl fitted on the chimney, The timber I use is well seasoned ash but I also burn smokeless coal designed for stoves ,swept the chimney last year ,and it seems fine when in use . Just a bit worried about lighting it now,

    • Hi Steve

      It’s almost certainly tar/creosote from deposits in the chimney. Step one would be to get the chimney swept again (this should be done at least once a year).

      Second step would be to look at sealing wherever the contents of the chimney are able to drip into the room.

      Thanks,

      Gr8Fires

  6. Hi. I have a new stove boiler that heats my rad & hot water. I have Moisture meter and all the timber I burn is always under 20% moisture. The wood I use is mostly from new 4×2 new timber cut offs and old dry roof trusts etc. Even 10 year old timber that I took out of an attic and should be bone dry contains 9 to 11% moisture? Like the other comments I have that sticky residue in my stove. I’m going to pick up some Kiln dry timber will that have 0% moisture? & if so will that produce sticky residue or burn off the sticky residue.Ventilation is perfect and I’m not over burning the timber. I don’t know how to stop the sticky residue.

    • Hi Noely

      If the roof trusses are treated, this could be responsible for the sticky residue (and it’s not a good idea to burn them for that reason).

      Also, if the are made of pine, this has a high resin content that causes sticky residue in woodburners.

      Thanks,

      Gr8Fires

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