Clay pot adaptors are used to increase the size of the flue on your stove be it 5" or 6" up to the require 8" which is the standard flue size in Ireland, although some older flues can be up to 10" in diameter.
It is near to impossible to get a flue 100% air tight to the clay pot as over time the heat will crack any sealant applied to the adaptor at the time of installation, this is common and usually is not an issue, but in cases were unseasoned timber with a moister content above 25% is been used (Timber with a moister content above 25% should never be used in your stove) tar residue can seep through this cap ,stain the flue and emit a unpleasant tar like odour throughout your home.
This can also be caused by a fire being light in a cold flue causing condensation to seep down the pots. If you would prefer to have a flue that is 100% sealed we would recommend a Stainless Steel Flexible Flue Liner.
Clay Pot Flue Adaptors