Why is the glass on my fireplace black?

One of the most common questions we get from our customers is regarding their wood burning fireplaces or stoves is “Why is the glass on my fireplace black?”

In this post we’ll outline the possible causes of black or dirty glass and their solutions. We should have you enjoying a clear view of your fire in no time!

Possible Cause #1 : Wet Wood

Hardwood with a moisture content of under 20% is the ideal wood for burning a hot, efficient fire. Wood that is too green or has a moisture content of above 20% is likely to be difficult to catch fire and to keep burning.

Telltale signs that your wood is too wet are if you hear excessive hissing, if it’s hard to catch, and if it produces more smoke than usual. This may be where your black fireplace glass is coming from.

Solution:

• Burn only properly seasoned wood that has a moisture content of under 20%.
• Test your wood with a moisture meter.

Possible Cause #2 : Burning non-wood materials

Nothing besides properly seasoned hardwoods should ever be burnt in your fireplace or stove. Things you especially want to avoid are plastic, cardboard, treated lumber, mouldy wood, magazines, etc.

It’s also important to never use lighter fluid or any other kind of chemical. Fire starters made for wood burning fireplaces are fine, as well as newspaper to get the fire going.

Solution:

This one’s easy, don’t burn any of the non-wood materials listed above!

Possible Cause #3 : Not enough draft

If there is not enough draft the smoke created by the fire isn’t being pulled up and out the chimney, it’s hanging around your glass, and turning it black.

Solution:

There are a number of reasons why a fireplace may not be drafting properly. Like we mentioned above, wet wood could be a factor. The flue may be colder than the air inside the house causing a backdraft. There may be another appliance in the room pulling air outside. The damper could be clogged, etc. etc.

The best solution is to have a chimney professional diagnose the issue.

Possible Cause #4 : Fire built too close to the glass

Having the fire burning right up against the glass is a surefire(!!) way to increase creosote buildup on the glass. Refer to your appliance manual to see which logs are the best size for burning in your fireplace or stove.

Solution: For newer appliances ensure your logs are at maximum 16 – 18″ long. Any longer than this and it’ll be hard to keep the fire far enough away from the glass to prevent creosote buildup. You’ll also run the risk of broken glass if a big enough log falls against it when the fire shifts.

Possible Cause #5: Chimney Height

Each fireplace or stove has specifications on how high the chimney needs to be to draft properly. The installation manual will give the proper firebox to flue ratio to produce the correct amount of draft for the size of your firebox.

Solution:

This is another issue where you will want to call a professional chimney installer to check if the chimney height is the cause of draft issues.

Other recommendations to keep your glass from turning black

• Heat the Chimney Before building the fire.
• Burn your fires hot!
• Ensure gasket on door is sealing properly.
• Ensure dry wood and proper draft.

How to clean your glass once it has turned black

All of the above is helpful to learn how to prevent your glass from turning black. But what if you have black glass right now?

Most importantly, do not use a household glass cleaner like Windex. It will leave a white residue that will burn onto the glass and cannot be removed.

Make sure your fireplace glass is cool. Wait at least a day since the last fire to make sure there are no embers which may be keeping the glass warm.

Use a purpose made creosote cleaner like Meeco’s Creosote Destroyer. Apply it using a micro-fiber towel or purpose made creosote applicator.

It will take a bit of time and elbow grease but it should come as clean as new.

What can we help you with?

Please let us know what maintenance or installation questions you’d like answered. We’ll always do our best to share what we know and help keep your fireplaces and stoves in top shape and burning for years to come.

We stock replacement parts for hundreds of models of fireplaces and stoves – check out our online store and if you can’t find what you’re looking for submit our parts request form and we’ll do our best to find it for you!