Blue Flame vs Yellow Gas Flame

Blue gas stove flames are good. 

Red/Yellow gas flames… not so much…

Blue flame vs yellow flame colour is an issue of safety, proper combustion and saving gas.

Gas flames are normally blue but sometimes they burn red or yellow when there is a problem.

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Natural Gas Blue Flame and LPG Gas (Propane) Blue Flame Colour – What Temperature is it?

A natural gas (methane gas) blue flame colour and an LPG (propane) gas blue flame colur burn in a different colour from other materials, like wood. For natural gas, the methane gas flame color is blue and the temperature is about 1,960°C. 

With complete combustion, an LPG (Propane) gas flame colour is blue and burns at a temperature of around 1,980°C, which is 20°C higher than a natural gas blue flame colour. See the flame color temperature chart below.

You get a blue gas flame with a hydrocarbon gas when you have enough oxygen for complete combustion.

When you do have sufficient oxygen, the gas flame appears blue because complete combustion creates enough energy to excite and ionize the gas molecules in the flame.

Not having a natural gas (methane gas) flame color blue or an LPG (propane) blue flame color, and having a yellow/red flame colour instead, could be indicative of an appliance problem.

Blue Flame vs Yellow Gas Flame Colour – LPG (Propane) & Natural Gas (Methane Gas) Flame Colour

LPG – propane – and natural gas (methane gas) flame colour are both blue. A blue gas stove flame colour and temperature means complete combustion, indicating you aren't wasting gas and money.

Red or yellow natural gas or propane gas flame color, instead of a blue flame, may mean signs of incomplete combustion, wasted gas and a serious safety hazard.

With hydrocarbon flames, such as gas, the amount of oxygen supplied with the gas determines the rate of gas combustion, flame colour and temperature.

In all but exceptional cases, like decorative propane gas fireplace flames, you always want a blue gas flame colour from a gas appliance burner.

Flame Colour (Color) Temperature Chart

On the following gas flame colour temperature chart, a blue LPG – Propane gas flame color means it burns at a temperature of around 1,980°C. A natural gas (methane gas) blue flame colour means it burns at about 1,960°C.

A yellow natural gas or LPG – propane gas flame color is indicative of incomplete combustion and carbon monoxide emissions. Yellow gas flames only burn at around 1,000°C.

Gas Flame Color Temperature Chart

Gas

Flame

Colour

Temperature

Chart

LPG (Propane) Blue 1,980°C
Natural Gas (Methane Gas) Blue 1,960°C
LPG or Natural Gas Yellow 1,000 °C
 Temperatures are approximate.
 Blue flame temperatures assume
 complete combustion.

Gas Fireplace Flame Color

A gas fireplace flame color is yellow and the exception to the rule. Gas fireplaces are typically designed to burn with an orange or yellow flame colour, not blue, for a more natural look.

Wood logs do not burn with a blue gas flame colour, so a gas fireplace flame color is yellow or orange for a realistic look and feel. It is also engineered to operate safely with that flame colour.

This means gas fireplaces break the rule of having a blue flame. They are also flued so there are no indoor emissions issues, should they produce some CO from the orange flames.

Gas Stove Temperature

Gas stove temperature is not the same as the gas flame temperature, which has a maximum of almost 2,000°C. The actual gas stove temperature range is typically from about 90°C to no more than 300°C.

Propane Torch Flame Temperature

Propane torch flame temperature is the same as other propane flames, at 1,980°C. Propane torch flame temperature colour would also be blue.

And Why is it Important?

It does make a difference. 

To understand all of this, we need to look at the background behind flames and combustion. 

The amount of oxygen supplied with the gas is the most important factor in determining the colour of the flame.  

Blue Flame Means Complete Combustion

A blue flame means complete combustion of the gas.

If you ever took a high school chemistry class and had a chance to use a Bunsen burner, you know how adjusting the air (oxygen) supply affects the colour and temperature of the flame. 

When you adjusted the Bunsen burner to increase the air supply you got more complete combustion, less soot, a higher temperature and a blue gas flame colour. 

With complete combustion, an LPG (Propane) flame burns at a temperature of around 1,980°C. 

For Natural Gas (Methane), the temperature is about 1,960°C, according to the flame color temperature chart.

Complete Combustion:

Gas + Oxygen = Water + Carbon Dioxide + Heat

Red/Yellow Flame Means Incomplete Combustion

A red, orange or yellow flame means incomplete combustion of the gas.

Again, remembering back to high school, if you starved the Bunsen burner of air, the combustion process was incomplete and the gas flame colour burned sooty red or yellow and at a cooler temperature. 

The yellow gas flame colour is due to incandescence of very fine soot particles that are produced in the flame. 

This type of flame only burns at around 1,000 °C, as noted on the flame color temperature chart.

Depending on the lighting, you may have actually seen the soot rising from the flame. 

What you didn't see was that incomplete combustion was also producing dangerous carbon monoxide.

When comparing different gases, you will discover that they required different amounts of air for complete combustion. 

To burn properly LPG (Propane) requires an air-to-gas volume ratio of about 24:1. 

For Butane, it is about 31:1. 

Natural gas (Methane) requires an air-to-gas volume ratio of about 10:1.

Incomplete combustion also results in hazardous carbon monoxide:

Gas + Oxygen = Water + Carbon Dioxide + Carbon Monoxide + Heat

Why Does a Blue Flame Mean it is Safer?

Stove Flame - Blue versus yellow gas flamesA blue flame means complete combustion is taking place. A key warning sign that you require gas appliance servicing is a yellow or red flame or a gas flame colour with a yellow burning tip. 

Other indicators include the accumulation of yellow/brown soot around the appliance, pilot lights that frequently blow out or an acrid smell and eye irritation. 

The exceptions to this are gas fireplaces and gas log fires that are designed to have a yellow gas flame colour.

The above are all indications of incomplete combustion. 

The result is that you could be wasting gas and/or generating dangerous carbon monoxide. 

The latter is a serious safety problem, if it occurs with an indoor appliance. 

If you observe any of these warning signs, you should schedule a service as soon as possible.   

The burner should be cleaned and checked for proper operation. 

Burners blocked with dirt can result in improper combustion, leading to soot build up inside the appliance. 

Flames in Gas Oven – What Colour Should the Flame be in a Gas Oven?

As with other gas appliances, the flames in a gas oven should burn with a blue gas flame colour, meaning complete combustion. The same applies to the flame color of propane or natural gas cooktops.

Why is There a Blue Flame in Burning LPG (Propane) Gas and a Yellow Flame on Burning Wood?

The LPG (propane) gas flame colour appears blue because complete combustion creates enough energy to excite and ionize the gas molecules in the flame. The exception is a gas fireplace flame color being yellow, for a more realistic look.

Burning wood has a yellow flame colour due to incandescence of very fine soot particles that are produced in the flame.

Depending on the lighting, you may have actually seen the soot rising from the flame.

Combustion and Carbon Monoxide (CO)

All gas appliances, domestic and industrial, produce water vapour, Carbon Dioxide and heat, and usually very small amounts of Carbon Monoxide.

If installed and maintained correctly, the operation of the gas appliance provides quick and efficient heating, cooking, hot water and more, and the products of combustion do not create any hazardous situations.

If an appliance is not correctly installed and maintained or has been modified, the products of combustion might change, and become hazardous to the people around the appliance.

Something as simple as a ventilation change (getting fresh air to the appliance to sustain complete combustion) may cause a gas appliance to malfunction, and create a hazardous situation for the people around.

Sometimes it is obvious when a gas appliance malfunctions.

Sooty smoke, red or yellow flames or poor performance are indicators, but sometimes no indicators are obvious.

If Carbon Monoxide (CO) is produced and escapes the appliance into the surrounding air, it will not be obvious (no smell and no taste) but will be very dangerous.

It is essential that gas appliances are correctly installed and serviced every two years, to maintain good combustion and safe, efficient operation.

Carbon Monoxide

Signs of carbon monoxide poisoning
Properly functioning gas appliances are quite safe. 
A blue flame is one indication of proper function and complete combustion.
As discussed, malfunctioning units may generate carbon monoxide, due to incomplete combustion. 
If you experience any signs of carbon monoxide poisoning while operating your indoor gas appliance, you should stop using it until it is serviced by your gas fitter.

How Does a Blue Gas Flame Colour Mean You Save Money?

A blue gas flame colour means complete combustion. 

This indicates that the gas is being burned efficiently without any unburned and wasted gas. 

With complete combustion you get the maximum heat output from your gas and use less gas to generate heat with whatever appliance you are using. 

You also minimise or eliminate the creation of carbon monoxide.

Final Thoughts

So, now you know why a gas flame burns blue and why it’s a problem if it doesn’t. 

Keep an eye on your gas appliances and have them serviced, as needed, to keep them operating properly and safely. 

Also follow the manufacturers' recommendations for periodic routine servicing.

Your family will be safer and you’ll save money, too.

 

 

 

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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.

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