Cloudy Stove Glass: Why It Happens and How to Stop It

Has the glass in your woodburner turned cloudy? If you’ve followed our top tips on how to clean woodburner glass and your stove glass is still milky, crazed or discoloured, there is likely to be more to the problem than the usual ashes and soot that accompany regular use of a wood-burning stove.

The most common explanation for a white residue that coats or clouds your stove glass is the presence of sulphur. And the most common reason for the presence of sulphur is that it’s contained within the fuel you’ve been burning.

When the fuel burns, the sulphur contained within it is released and mixes with water to form sulphuric acid. There is always likely to be a ready supply of moisture on your newly lit stove in the form of condensation, which means that corrosive sulphuric acid is created can cause damage to the glass and other surfaces it settles upon.

Over a period of time, this will result in cloudiness or discolouring of the stove glass as the sulphuric acid. etches itself into the surface of the stove glass. When your woodburner heats up, the moisture within the sulphuric acid evaporates and leaves behind sulphur dioxide and sulphur trioxide, which are white powders.

Cleaning cloudy stove glass

Unfortunately, if you’ve tried cleaning the stove glass and the cloudiness isn’t budging, there isn’t a great deal you can do to improve the situation. You can’t remove discolouring, milkiness or crazing that has been caused by sulphuric acid.

Wiping the glass with a damp cloth might initially seem to resolve the problem, but in fact you will only be recreating the sulphuric acid. As soon as the glass dries or the moisture evaporates, the white powder – trapped within tiny cracks in the glass surface – will return and with it the cloudy effect on your stove glass.

The good news is that the damage will not have any effect on how the stove operates. The glass is not weakened and your stove will continue to perform exactly as it always has. The only issue is an aesthetic one. If you really can’t bear to have your view of the flames obscured by cloudiness, the only option is to buy replacement stove glass.

Of course, once you have replaced your stove glass you will be keen to avoid the same thing happening again. Let’s take a look at how to do that…

How to stop stove glass going cloudy

Check your stove manufacturer’s instructions on what fuels should be burned on your appliance. This varies between different stoves, so it’s always worth checking what your manufacturer has to say on the matter.

Avoid burning fuels that have a high sulphur content. Household coal (also known as bituminous coal, house coal and smoky coal) has high levels of sulphur. Petroleum coke (or pet coke) also contains a lot of sulphur.

Ensure your fuel is dry. Burning damp or wet fuels will heighten potential problems with sulphur, so make sure your stove is stored in a dry place. When you buy fuel that might have been exposed to the elements before, give it a chance to dry out properly before burning it. Similarly, if you’re burning wood, make sure it’s well seasoned before use.

Don’t slumber your stove. Allowing your stove to burn for extended periods without adding more fuel results in an inefficient burn that encourages the release of gases like sulphur and increases the likelihood of them condensing within your stove system. At the end of the evening, open the air vents fully to burn any remaining fuel rather than allowing it to slowly burn out of the coming hours.

Use your airwash system. The airwash system found on the majority of modern stoves creates a thin layer of air that washes over the inside of the stove glass and helps to prevent sulphuric acid and other substances from settling on the glass.

Clean your stove glass regularly. Giving your stove glass a clean (always when it is cold) will help to remove any harmful sulphuric acid that has settled on the surface before it gets the chance to cause permanent damage.

Clean ashes out regularly. A build-up of ashes again glass will increase the chance of sulphur contained within the ashes condensing and causing cloudiness.