Friday, June 24

Why Stove Glass Blackens and How To Get the Most from an Airwash System

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After a few uses, you might be noticing that your stove’s glass is not as clean as it should be. It could be that the glass has blackened or crazed (fine cracks on the surface).

This is preventable, however, so read on for a guide to getting the most from your stove’s airwash system.

Wood Type

How much firewood do you need for a log burner?

The Issue

Poor fuel choice can lead to an inefficient burn within the stove, which can disrupt the airwash system as well as causing additional particles to build up on the glass, making it hard to clean.

What to Avoid

Avoid burning woods that have been treated, such as pallet wood and fence panels. It is also worth avoiding woods that contain sap, such as pine or fir.

The Solution

Use a good quality hard wood such as oak, beach, hawthorn or oak. Well seasoned/dry hardwoods burn slowly, cleanly and produce a better heat output.


Moisture Content 

The Issue

Your wood should have a moisture content between 15% – 20%.

If the moisture content is above this, it can cause the fuel to smoulder rather than burn. This will cause a high amount of smoke within the fire chamber leading to particulate build up on the glass.

The Solution

Use a moisture metre on your fuel to ensure the moisture content is between 15% – 20%, if you find that it above 20% leave the fuel to dry a little while longer.


Airwash Air Controls


The Issue

The airwash (or secondary air control) can, in most cases, be opened and closed to give additional control over the fire. Pushing this air slider to the closed position, will cut off the curtain of air that acts to keep the glass clean.

The Solution

Keep the secondary air control lever open as much as possible. Although this will cause the fire to burn quicker, it is the best way to keep the glass clean.

If you do close the lever for additional control over the fire, soot will begin to build up on the glass, opening the lever back up for a hotter burn should clear the build up back off the glass.

Overloaded Stove

The Issue

An overloaded stove can cause 101 problems, but for this guide we’ll stick with how it affects the glass.

Your stove is designed and tested to burn in a particular manner, with air flowing freely around the fuel. Putting too much wood into the stove will disrupt this air circulation, causing an excess of smoke and hampering the performance of the airwash system.

The Solution

Try running the stove with fewer logs, we recommend two average size logs for your size of stove, if you’re using one of the hardwoods mentioned earlier in this guide your stove should still be giving out it’s rated output on this amount of fuel.

Fuel Mix

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The Issue

Mixing smokeless coal and wood together is never recommended, smokeless coal produces sulphur and wood creates moisture when burnt. Sulphur combined with moisture creates sulphuric acid which may not cause blackening, but will instead create a “crazing” on the glass.

The Solution

Try to burn only one type of fuel at anyone time. Stick to burning only wood OR smokeless coal. If you must mix the two allow the one type of fuel to burn down to embers before adding the new fuel type.


You can find guides on all manner of stove related subjects by browsing the Direct Stoves Blog. You can also head to the Direct Stoves website to find yourself a brand new Wood Burner, Gas Stove or Electric Stove.

Discover more articles below

What Chimney Cowls Are Best for Stoves? How Much Does It Cost to Run a Log Burner? 
 | A Complete Guide to Buying Firewood for Your Log Burner


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