What are the problems of burning wet wood?

Potential dangers from burning wet wood

Problems of burning wet wood

Burning wet firewood can result in two very serious problems associated with condensation in the chimney.

Water vapour combines with other gases and particles going up the chimney and unless the chimney is kept warm, the condensation forms a creosote-like substance which hardens to form tar on the surface of chimney liners and may seep into brickwork in an unlined chimney. Wet wood causes the chimney to cool and so condensation occurs and a residue is formed.

Blockages and chimney fires

The residue is brown or black and can be flaky, sticky, runny, tar-like or hardened and will sometimes be all of these in the same flue. The chimney may become completely blocked or the volatile residue can ignite causing a dangerous chimney fire.


The excessive condensation from wet wood which normally forms in the upper part of the chimney is acidic in nature and will corrode the inner surface of a metal liner, eventually leading to perforation and failure of the liner.

Chimney Keep your Chimney Clean

Having your chimney swept regularly will help your fuel burn more efficiently, and minimise any risk of damage to your appliance or chimney. The following frequencies are the minimum recommended by the Guild of Master Chimney Sweeps. Your chimney sweep will be able to better advise the correct sweeping frequency for your situation.

  • Smokeless Coal – At least once per year
  • Wood – Up to four times per year
  • Bituminous Coal – Twice per year

Visit the Guild of Master Chimney SweepsNACS, or APICS to find a reputable, reliable sweep near you.

Fit Smoke and Carbon Monoxide Alarms

Smoke and Carbon Monoxide detectors should be fitted in every home, whether the owners burn solid fuel or not. An audible alarm will alert you to any danger wherever you are in the house. Carbon Monoxide is a colourless, odourless, and tasteless gas which can be fatal if inhaled in large quantities. A Carbon Monoxide alarm is a reliable way of detecting carbon monoxide before it reaches dangerous levels.

Fire and Chimney Safety Tips 

  • Don’t store wood or other flammable materials next to your fire or stove
  • Try to use wood that is dried to 20% moisture or less
  • Don’t leave open fires unattended
  • Use a fire guard when necessary
  • Have your chimney swept regularly
  • Use audible smoke and carbon monoxide detectors

To read DEFRA's guide to open fires and wood-burning stoves, click here.

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