At this time of year when the weather gets cold enough to start affecting your fire or stove you may be surprised or even shocked when things don’t seem to work the way they normally do.
Appliances have Running Temperatures
Stoves, indeed all appliances have a running temperature and it takes time to reach this point, so you may find they won’t start up so easily and/or are Smokey for the first 10-15 minutes. This is due to the cold air dropping down the flue and stopping the updraft of hot air trying to rise but once up to running temp the hot air rising displaces the cold air as it pushes its way up and out the chimney flue.
One way to overcome this problem is to try heating the metal baffle plate with a blow torch before attempting to light your fire. Or if it is not metal, you could try the Scandinavian method of building your fire kindling upside down i.e. paper on top> kindling>wood/coal.
** NB// This updraft problem is particularly prevalent in flues on the gable end of your building and if the flue space is big too, then you may need to have your liner wrapped in an insulation jacket or the flue space backfilled with vermiculite. **
Tar or Black Liquid Formation
Recently, a customer called worried about black liquid tar coming down into their stove. You too may have found a sticky, black liquid in your wood-burning stove and you might have spotted it running down the inside walls of your appliance or settled somewhere in the firebox. The consistency reminds you of tar because that is exactly what it is.
If you have seen this black liquid, it indicates that you are not operating your stove correctly and in particular , burning unsuitable (damp) fuel.
Usually tar is created as a by-product of burning logs on a wood burner when the moisture level of the wood is too high. Since energy is being wasted evaporating water, the stove doesn’t get up to a 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 cold metal of the flue liner.
The condensed gases will either solidify on the inside or the flue or start to 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 highly flammable creosote in your stove system significantly increases the risk of chimney fires. This is especially true if you burn soft wood such as pine, the resin being the main culprit.
How to stop the black liquid appearing in your wood burner
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 (<15-20%), this is easily achieved by using a moisture meter.
Ensuring there is a strong draw up your chimney, operating your stove at full capacity and burning it with the air intake fully open for 10-15 minutes once or twice a day will blast off the vapor and burn any sediment that settles on the flue. You can also try using some table salt on the burning wood to try to help absorb any water that is created. Finally, not slumbering your stove over night and also ensuring your room is well ventilated (especially if you keep damp logs in the room too) will minimise the chance of flue gases condensing in your chimney.
It is also important to get your chimney swept regularly as this will remove any residual creosote that has built up in your chimney and prevent it seeping back down your chimney and into the stove. Regular sweeping will also protect your liner from corrosion and eventual destruction.
