Jøtul F 373 Advance with soot on the fireplace glass

Why does a fireplace become sooty?

Much of the pleasure of having a fireplace or wood burner is being able to see the flames of the fire through the large glass panes. So it can be frustrating to find that your view of the fire is becoming blocked by soot and pitch on the glass. Let us explain why this happens and offer some tips on how to prevent it.

Why you get soot on the glass

If the temperature inside the fireplace is too low, it is more likely that soot and tar will settle like a blanket in the burn chamber and on the glass. Usually this is because the wood you are burning is too moist or the draft is not strong enough.

Use dry wood

Moist firewood lowers the temperature inside the wood burner or fireplace. This causes poor combustion and frequently leads to soot formation. Remember that fresh wood needs to be left to dry for at least six months or preferably one year before it is dry enough to use. It should then be stored in a way that does not cause the quality of the wood to deteriorate. The drier the wood, the more heat! When we say that firewood needs to be dry enough, we mean it should have a moisture content of less than 20%. Firewood with a moisture content of more than 20% produces 10 to 30 times more soot and particulate emissions than dry, seasoned wood does.

Hand which grasping dry wood

There are several ways you can measure moisture content:

  • A moisture meter offers the most accurate means of measuring the moisture level of firewood.
  • You can also bash two logs together. If it sounds like you’re hitting a ball with a bat, it’s a good sign that the wood is dry. If it produces a dull thud, the wood is not dry enough.
  • You can smear washing-up liquid on one end of the log and blow into the log at the other end. If soap bubbles come out at the far end, the wood is dry.

Prevent soot with a good air supply

It is important before you start to light a fire in your fireplace to ensure there is a good supply of air. Once again, make sure the wood is dry and is finely split and that the air vent(s) are fully open.

The hand regulates the air supply in the fireplace

To get the fire going properly, it can be a good idea to leave the door of the wood burner or fireplace slightly ajar for a few minutes. The temperature of the fire will then rise quickly and the fire will be burning with complete combustion and clean exhaust gases – which means less soot.

If you are struggling to get your fire going properly because the draft is not strong enough, we have a few more tips that might help.

How to light a fireplace

Light the fire from the top down!

The way the fire is started also affects the amount of soot and particles produced by the fire before combustion is optimal. The most environmentally-friendly method is to light the fire from the top, which ensures a better air supply and makes the first load of wood last longer and burn better.


How to light your fire

Glass stays clean in wood burners with air wash

Did you know that many of our wood burners and fireplaces have an air wash system and glass coating that help to keep the glass clean while the fire is lit? And if any soot does settle on the glass, it is usually enough to get the fire burning briskly for a short period. The heat and air wash system ensure that any soot on the glass is burned away.

How to clean the fireplace glass

If you want to clean traces of soot off the glass, the simplest and most environmentally-friendly way is rub it off using paper and ash.