You light the stove, the wood burns, the house is warm. But when cleaning, you discover a black, shiny, sticky layer in the flue pipe or chimney. Sometimes it even resembles asphalt and smells unpleasant.
“That’s just soot,” you tell yourself.
But beware! It could be tar. And it’s no longer just about a dirty chimney.
Soot or tar? They’re not the same thing!
Soot is typically a black, dry, powdery deposit that is produced during combustion processes.
Tar deposits, on the other hand, can be sticky, viscous, shiny, and even very hard when hardened.
Both substances can accumulate in the chimney, but particularly thick tar deposits pose a serious risk because they are flammable and can contribute to a chimney fire.
Why is tar formed?
Put simply: Burning wood also produces substances that, under unfavorable conditions, do not burn completely. If the exhaust gases cool down too much, these substances can deposit on the walls of the stove, the flue pipe, or the chimney.
And what is the most common contributing factor?
1. Wood too damp
“I’ve had it for three years!”
Okay, but where? In the rain or in a well-ventilated wooden shed?
Damp wood cools the firebox and worsens combustion conditions. This can lead to increased smoke and tar deposits.
2. Stove too narrow
If you want an application to last as long as possible, close the air supply almost completely.
The fire will begin to smolder, but instead of providing efficient heat, it may produce more smoke and debris.
Proper operation according to the manufacturer’s instructions is sufficient. Continuous fire suppression outside of the recommended conditions is not permitted.
3. Exhaust gas too cold
The problem may not be solely due to the wood or the service.
When flue gases flow through an improperly constructed, undercooled, or unsuitable chimney, condensate and tar deposits can form on its walls.
Therefore, it is important that the oven, flue and chimney form a properly constructed unit.
Would it help if I heated it up really hard and burned off the tar?
You absolutely should not try that!
The deliberate burning of tar by heavy flooding can cause a chimney fire, damage it, and endanger the entire house.
If you notice large tar deposits, have your chimney inspected and cleaned by a professional. Hardened tar may not be removable by regular sweeping.
How can tar formation be prevented?
The basis consists of a few simple principles:
- Use sufficiently dried wood for heating, usually with a moisture content below 20%, unless otherwise specified by the manufacturer.
- Adhere to the recommended fuel dosages and combustion air settings.
- Do not try to prolong the burning by constantly stoking the fire.
- Have the exhaust system cleaned and inspected regularly at the prescribed intervals.
- If tarring is repeated, the suitability and function of the chimney and the oven itself should be checked.
Our final piece of advice
The chimney is not a place where everything that wasn’t burned in the oven should end up.
If you notice significant tar deposits, do not ignore them. Simply wiping the soiled door and using a slightly drier piece of wood next time is not enough.
Have the condition of the exhaust system checked and the cause determined.
A properly functioning stove is meant to heat your house. Never light a fire in the chimney.