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Gas Fireplace Logs Turning Black? Here’s Why (+ How to Fix)

Gas fireplaces will usually have imitation logs made from ceramic fibers or refractory cement to offer better aesthetics and similarity to traditional wood fireplaces. The logs are designed to be fireproof and maintain the same look and feel as when you bought them. So, if your gas fireplace logs are turning black, does that mean they’re burning?

Your gas fireplace logs are turning black because they’re collecting soot. Vented gas fireplaces will naturally collect soot with time. Other reasons include incorrect log placement, chemical residue on the logs, clogged burner ports, improper airflow, and an old burner set.

In this article, I’ve put together a detailed list of all the major reasons why your gas fireplace logs are turning black. Following that, I’ve also provided a short step-by-step guide on cleaning blackened gas fireplace logs.

Reasons Why Your Gas Fireplace Logs Are Collecting Soot

If your gas fireplace logs are turning black, it’s improbable that they are getting burnt. The imitation logs are made from non-flammable materials and won’t catch fire or start to melt. 

As such, if the logs are getting black, they’re collecting soot on their surface. Now, many things can cause soot buildup on your gas fireplace logs. Some of these causes are natural, while others are due to faulty components, which you’ll need to fix.

Here are 7 reasons your gas fireplace logs are collecting soot:

  • You have a vented gas fireplace.
  • The gas fireplace logs are incorrectly placed.
  • The air-to-fuel ratio is off.
  • There’s chemical residue on the logs.
  • The burners aren’t covered with sand or embers.
  • The burner ports are clogged.
  • The burner set is old.

Let’s go over each of these reasons in more detail.

1. You Have a Vented Gas Fireplace

Is your gas fireplace vented or ventless? Vented gas fireplaces are the ones that have an attached flue. 

If you’re using a vented gas fireplace, it’s natural and completely okay for the logs to gradually turn black as they collect soot. 

You might have heard that gas fireplaces deliver a clean fire with barely any soot formation or residue. This is mainly true for ventless gas fireplaces. A vented gas fireplace does produce some soot in the burning process, albeit not as much as a traditional wood fireplace.

In most cases, this happens because the vented gas fireplace is configured to produce a yellow flame. This gives it an authentic look but also causes incomplete combustion leading to soot formation.

Over time, the soot from your vented gas fireplace will settle on the imitation logs, giving them a black appearance.

Thankfully, you can easily clean off the soot, and the logs will look good as new again.

Alternatively, you can also call an HVAC technician and have them reconfigure the vented gas fireplace to a blue flame, which is cleaner and will create less soot.

Please bear in mind that soot buildup on gas logs is only common with vented gas fireplaces. If you have a ventless gas fireplace where the logs turn black from collecting soot, something is wrong. In this case, you should call a technician to have the gas fireplace examined.

2. The Gas Fireplace Logs Are Incorrectly Placed

Whether you have a vented gas fireplace or a ventless one, incorrect log placement can affect the flame and cause excessive soot formation. This soot will eventually settle on the logs, turning them black.

The imitation logs are provided to help give the heating appliance an authentic and classy look. You can move the logs to customize the gas fireplace. In fact, you might even want to place the logs such that it comes in contact with the flame – making it seem like the logs are burning.

However, sometimes you can accidentally place the logs too close to the burners, causing them to interfere with the path of the flame. This causes incomplete combustion of the fuel, ultimately leading to excessive soot formation.

As such, if you notice heavy soot buildup on your gas logs, check to see if they are too close to the burners. If they are, rearrange them so that they don’t block the flame as it’s coming out of the burner.

If you’re into decorating your gas fireplace with your logs, I suggest getting a non-combustible platform, also known as a combustion matrix. These will make your gas fireplace look even more traditional and classy. Plus, it will ensure there’s enough space for the flame to burn properly.

3. The Air-to-Fuel Ratio Is Off

The quantity of air required to perfectly burn a set quantity of fuel is known as the air-to-fuel ratio. If this ratio is off because there’s less air, some of the fuel won’t burn completely, resulting in soot. 

As such, your gas fireplace needs to have the proper amount of airflow to ensure the gas burns cleanly and produces as little soot as possible.

Use Built-In Devices to Manage Airflow

So, how do you make sure the gas fireplace has enough air to play with? Well, the heating appliance should have in-built devices to help you adjust the airflow.

For instance, an open-front gas fireplace should have an air shutter, possibly located on the gas line. You should be able to adjust this to increase/decrease the airflow in the fireplace chamber.

Similarly, with gas fireplaces that have a glass door, you should be able to adjust the vent shutters located underneath the door to control the airflow.

You can also look at the user manual that came with your gas fireplace to learn how to adjust the airflow in your particular unit.

The goal is to adjust the airflow such that the gas fireplace produces a yellow flame with minimal soot formation. That said, you can also increase the airflow to get a more bluish flame—which means a clean fire—if you want to minimize soot as much as possible.

That said, always remember to keep these air intake vents clean. Over time, these can get clogged with dirt, pet dander, and other small dust particles, preventing proper airflow. 

As such, routinely clean out the air intake vents every few months to ensure optimal airflow and low soot formation.

4. There’s Chemical Residue on the Logs

If you’re using a cheap gas log, it might have a coating or paint job using chemicals that are not highly heat resistant. In that case, when you place the logs inside the gas fireplace exposed to high heat, the chemicals can start to burn, creating a black appearance.

You can easily tell whether you have burnt chemicals or soot on your gas logs by observing the texture. 

In case of soot buildup, the gas logs will have a powdery or dusty black deposit. If the blackness is coming from chemicals burning, the residue might have an oily texture, or it might flake off, exposing the ceramic or cement layers of the logs.

Now, the simplest way to avoid this problem is by getting high-quality logs for your gas fireplace.

That said, even high-grade gas logs can suffer from blackening from chemical residue. This happens if you previously cleaned the logs with an incompatible aftermarket cleaner. 

The logs might still have some cleaner solution stuck to them as you put them back inside the fireplace and start a fire. The harsh chemicals in the cleaner can burn and char the gas logs.

5. The Burners Aren’t Covered With Sand or Embers

Some gas fireplaces recommend covering the burners with sand and embers. This spreads the flow of the gas fuel and ensures a proper air-to-fuel ratio. 

Other than this, the sand and embers also have a decorative purpose: creating the illusion of a real fire. 

Sadly, most people are only aware of the sand’s decorative use. Furthermore, some just don’t appreciate its aesthetic contributions and decide not to use them in their gas fireplace. This is a big mistake.

Some gas fireplace setups burn too vigorously. Without the sand and embers to hinder the gas flow, it can lead to incomplete combustion causing soot formation. As I mentioned before, this soot will settle on the logs and turn them black.

As such, if your gas fireplace recommends the use of sand and embers, know that it serves a function and isn’t there just for aesthetics. Ensure the burners are properly covered (not directly) with the material, and the soot buildup should stop or decrease.

For reference, here’s a short 1-min YouTube video on placing embers on gas log burners:

6. The Burner Ports Are Clogged

The burner on your gas fireplace has numerous small pores called the burner ports that release a steady stream of gas into the combustion area. 

Each port has a very small diameter and will only release a small amount of gas. This design helps create a fire that looks properly spread out, as you’d find on a traditional wood fireplace.

However, the problem with having small burner ports is that they can get easily clogged up. With time, dust, dirt, broken gas log fragments, insect nests, and even little amounts of soot can block the burner ports and prevent gas from passing through.

This restriction can potentially tamper with the air-to-fuel ratio. In some cases, this will cause incomplete combustion, generating more soot. The excess soot will ultimately lead to more burner ports getting clogged up. While all of this is happening, your gas logs will get blacker and blacker from collecting all that soot.

Thankfully, you can easily avoid such mishaps by routinely cleaning and servicing your gas fireplace. Ideally, you should service ventless gas fireplaces annually and vented gas fireplaces twice a year.

7. The Burner Set Is Old

If you have a really old gas fireplace with an old burner set, that might be the root of all that soot.

As the burners on your gas fireplace get older, they wear out and start to rust. Sometimes, the burners can form a crack, causing excess gas to release. 

Overall, an old burner set won’t be able to maintain the same volume of gas emission that a newer burner set can. This will inevitably hamper the overall combustion process and can potentially cause soot formation if the air-to-fuel ratio is affected. 

That said, replacing your old burner set with a new one will solve this issue and stop your gas logs from turning black.

How To Clean Dirty Gas Fireplace Logs

Now that you know what’s making your gas logs turn black, you can fix it and stop the problem. But what about the black soot deposits left on your gas logs?

Here’s a step-by-step guide on how to clean dirty gas fireplace logs:

  1. Put out the fire in the gas fireplace and turn off the gas supply.
  2. Wait for an hour or two for the gas logs to cool down.
  3. Remove the logs and place them on old newspapers or a drop cloth. Don’t directly put them on your carpet, as that can lead to a nasty stain.
  4. Use a brush to gently scrub off the soot buildup on top of the logs. You can also use a vacuum cleaner for this process.
  5. Now take a dry microfiber cloth and wipe down the remaining soot on the logs. If the soot is too stubborn to come off easily, you can use a soft scrub brush.
  6. If the logs still have some black soot spots, check the log’s user manual to confirm if you can use water to clean them. If the manual deems it appropriate, take a damp washcloth and work away at the spots till they are squeaky clean.
  7. At this point, you can also try using manufacturer-recommended gas log cleaners. Remember to follow the instructions, so you don’t accidentally damage the logs.
  8. Once the logs are cleaned up, bring your attention to the gas fireplace. If the logs are covered with soot, the fireplace chamber should be too. As such, clean the gas fireplace before placing the logs inside it.

And that’s it! You have successfully cleaned your blackened gas fireplace logs.

Key Takeaways

Your gas fireplace logs are turning black mainly because they’re collecting soot. 

This naturally happens in vented gas fireplaces. However, soot formation can accelerate if the logs are incorrectly placed, the air-to-fuel ratio is off, the burners aren’t covered with sand or embers, the burner ports have gotten clogged, or the burner set is old and rusty.

Chemicals from cheap gas logs or previously used cleaning liquids/sprays can also leave a blackish residue on your gas logs.


  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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