Simply put, you have too much air mixed with the gas. It is a common problem that is easily solved.
By reducing the amount of air mixing with the gas before it gets to the burner, the color changes from blue to yellow. The more air it pulls from the environment, the more yellow it becomes.
What Makes the Flame Yellow?
When you see yellow in the flames of your gas fire pit, you’re seeing unburned carbon. The bits of carbon are heated to the point that they are incandescent and producing a yellow light. It’s the same principle as that of incandescent light bulbs. Electricity is passed through a carbon filament making it hot enough to produce that glowing yellow light we associate with old-fashioned light bulbs.
With gas fireplaces and fire pits a yellow flame is achieved by reducing or eliminating the air mixed with the gas. This results in the incomplete combustion of the carbon molecules in the gas. That incomplete process leaves leftover carbon that is heated and produces a yellow glow to the flame.
A blue flame is caused by too much air mixed with the gas. In essence, it makes the burn too efficient. All of the carbon is burned off and that results in a blue flame. Unburned carbon is what gives the flame a yellow color.
How to Make a Gas Fire Pit Flame Yellow
Quite simply, to make the flame in your gas fireplace or fire pit yellow, reduce the amount of air mixed with the gas.
In the case of propane, it’s pretty straightforward. You’ll want to reduce the amount of air coming into the air mixer. (Because of the density of propane, all propane systems utilize an air mixer.)
Propane’s high carbon content makes it much easier to create a yellow flame; however, the more yellow the flame, the dirtier the burn. That desirable yellow color is produced by unburned carbon. The unburned carbon left behind is a black residue known as soot. You are looking for the middle ground—a pleasing yellow flame with minimal sooting. To reach this goal, it’s important to be using the appropriate air mixer for your burner.
Note: Make sure your air mixer is properly matched to the Btu rating of your fire pit burner. If not, the air/gas ratio will be off and can cause excessive sooting. If you are unsure about your set-up, check out our article: Propane Air Mixers – Everything you Need to Know (and then some!)
Things get trickier with natural gas. It has a lower carbon content than propane, so it is more difficult to get a yellow flame.
In fact, it’s not possible to remove all the blue color from the flames in your natural gas fire pit or fireplace. Even when you prevent any air from mixing with the gas, you’re still likely to see some blue color at the base of the flames. There simply isn’t enough carbon around to burn.
If you aren’t seeing any yellow components to your flame, or very little, consult with your licensed gas installer for guidance.
Why Do We Crave a Yellow Flame?
Due to its chemical make-up, wood burns yellow. Maybe there is something primal about the nature of a wood-burning fire in our primitive past, or maybe it just denotes warmth and nostalgia. Whatever the reason, yellow is the goal.
Natural gas and propane are hydrocarbons. They create the color blue when they burn.
Household gas appliances should always have a blue flame because it denotes a clean, safe, and efficient burn. However, gas appliance manufacturers recognize the desire for a yellow flame in certain applications where wood was traditionally used.
They understand that consumers want to mimic the look of a wood-burning fire in their gas fireplaces and fire pits. So, a yellow flame is more desirable, even if it isn’t the most efficient. To this end, industry experts have worked hard to develop a way to get closer to a yellow flame, while still being safe and reasonably efficient. This solution isn’t perfect, and it may not look exactly the same as wood, but it’s close enough for most of us!