Blue flame versus yellow flame colour is a question of complete combustion versus incomplete combustion. LPG (propane) and natural gas (methane) flame colour are both blue. A blue flame colour and temperature means complete combustion. Red flames or yellow gas flame colour may be a sign of incomplete combustion, wasted gas and a serious safety hazard. Blue flame versus orange flame, blue flame versus red flames and blue flame versus yellow flame are all the incomplete combustion issue.  

Blue flames are good. 

Red flames and yellow gas flames... not so much...

Blue flame versus red flames is an issue of safety, proper combustion and saving gas.

Gas normally burns with a blue flame but sometimes it burns with yellow or red flames when there is a problem.

Flame Colour Meaning

Flame colour meaning can be indicative of temperature, type of fuel or the completeness of combustion. For example, a blue flame is the hottest followed by a yellow flame, then orange and red flames. Hydrocarbon gases burn blue whilst wood, coal or candles burn yellow, orange or red. A blue gas flame colour is also indicative of complete combustion.

What Does Blue Flame Mean - Blue Flame Means Complete Combustion

A blue flame means complete combustion of the gas. With complete combustion, LPG (Propane) burns with a blue flame. Pure hydrocarbons like methane (refined natural gas), propane, butane and ethane gases also burn with a blue flame. These gases are all alkanes and are gas that burns with a blue flame.

These gases come from raw natural gas processing and oil refining.

An LPG burns with a blue flame at a temperature of around 1,980°C, as noted on the flame colour temperature chart.

For Natural Gas (Methane), the blue flame temperature is about 1,960°C.

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 flame colour. 

 

Yellow or Red Flames Means Incomplete Combustion

An orange, yellow or red 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 as sooty yellow or red flames and at a cooler temperature. 

A blue flame indicates complete combustion of the carbon, which is why you see a blue flame with gas appliances. Propane is a hydrocarbon, containing carbon atoms. A blue flame is indicative of complete combustion versus a yellow flame or orange flame.

The yellow or red flames are due to incandescence of very fine soot particles that are produced in the flame.

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

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

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

Incomplete combustion of LPG Formula results in hazardous carbon monoxide:

LPG Gas + Oxygen = Water + Carbon Dioxide + Carbon Monoxide + Heat with Yellow Flame

What Colour is Natural Gas

Natural gas has no colour. Natural gas is clear and odourless, in its natural state. The smell that people associate with natural gas is added to it for safety reasons. The stench alerts us to gas leaks that might otherwise be undiscovered.

What Colour Does Methane Burn - Methane Gas Colour

Methane does burn with a blue flame colour, when there is complete combustion, with a methane gas flame temperature of approximately 1,960°C. Methane gas does also burn with a yellow, orange or red colour, when there is incomplete combustion, with a methane gas flame temperature is about 1,000 °C.

Ethane, propane, butane and isobutane do also burn with a blue flame colour.

Methane gas is the primary constituent of natural gas and it burns with a blue colour flame. If there are yellow, orange, or red flame colours when your methane burns, it is indicative of incomplete combustion. Other colours may also appear, indicating other substances burning within the methane.

 

 

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

A proper natural gas appliance flame colour is a vigorous blue colour flame with a lighter blue colour section within the middle of the flame. A small yellow colour tip may be present. A blue natural gas flame colour is indicative of proper combustion and minimal wasted gas.

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

A natural gas blue flame indicates that the burner is providing the correct air-fuel mixture, with sufficient oxygen for complete combustion at the burner. A blue flame burns the fuel completely producing carbon dioxide, water and heat.

The natural gas flame temperature is about 1,960°C. Natural gas burns with a blue flame colour, with complete combustion. LPG (propane) also burns with a blue flame colour. With complete combustion, an LPG (Propane) gas burns with a blue flame and burns at a temperature of around 1,980°C, as noted on the flame colour temperature chart.

LPG blue flame colour burns 20°C higher than a natural gas blue flame colour. See the flame colour temperature chart below.

Both natural gas and LPG burn in a different colour from other materials, like wood.

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.

What Colour is Natural Gas

What colour is natural gas can be answered in two ways. Natural gas itself is a colourless gas whilst a natural gas flame burns with a blue colour.

What Gas Burns with a Blue Flame

Gas that burns with a blue flame includes pure hydrocarbons like methane (refined natural gas), propane, butane and ethane. These gases come from raw natural gas processing and oil refining. These gases are all alkanes and are gas with a blue flame.

There are copper compounds that burn with a blue flame including Copper(I) chloride, commonly called cuprous chloride (CuCl), Copper carbonate (CuCO₃), Copper arsenite (CuHAsO₃) and Copper sulphate CuSO₄.

Blue Flame versus Red Flames Colour - LPG (Propane) & Natural Gas (Methane Gas) Flame Colour

LPG - propane - and natural gas (methane gas) both burn with a blue flame colour. A gas stove blue flame colour and temperature means complete combustion, indicating you aren't wasting gas and money. See the flame colour temperature chart below.

Red flames or propane-natural gas flame colour orange, 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 LPG-propane gas fireplace flame colour, you always want a blue flame colour from a gas appliance burner.

Flame Colour Temperature Chart - Gas Flame Colour - Fire Colour Chart - Blue Flame - Red Flames

On the following gas flame colour temperature chart (fire colour chart), red flames or a yellow natural gas or LPG - propane gas flame colour is indicative of incomplete combustion and carbon monoxide emissions. On the flame colour temperature chart, red flames or yellow gas flames only burn at around 1,000°C.

Blue and Yellow Flame

As it relates to hydrocarbon gases, blue flame is indicative of complete combustion whilst a yellow flame indicates incomplete combustion. An LPG blue flame also burns hotter, at around 1,980°C, versus about 1,000°C for a yellow flame.

Propane Flame Colour

Propane flame colour is a blue flame colour on the flame colour temperature chart, with complete combustion, and burns at a temperature of around 1,980°C.

Natural Gas Flame Colour - Natural Gas Flame Colour Orange - What Colour Does Methane Burn - Methane Gas Colour

The flame colour changes to orange, yellow or red flame and the flame wavers. The yellow/orange/red colour is created by carbon soot particles in the flame, produced as the result of incomplete methane gas combustion.

With complete combustion, methane burns with a blue flame colour (natural gas blue flame) and burns at a temperature of around 1,960°C. Natural gas flame colour orange indicates incomplete combustion. What colour does methane burn is the same question and the answer is a blue methane gas colour and burns at a temperature of around 1,960°C. See the flame color temperature chart below:

Flame Colour Temperature Chart

Gas Flame Colour Temperature Chart (Fire Colour Chart)
Gas	Flame Color	Temperature Chart
LPG (Propane)	Blue Flame	1,980°C
Natural Gas (Methane Gas)	Blue Flame	1,960°C
LPG or Natural Gas	Yellow or Red Flames	1,000 °C
Temperatures are approximate.  Blue flame temperatures assumes  complete combustion.

Propane Gas Furnace Flame Colour

Propane gas furnace flame colour is the same as propane flame colour. Propane furnace flame colour is a blue flame colour on the flame colour temperature chart, with complete combustion, and burns at a temperature of around 1,980°C.

Gas Fireplace Flame Colour

A gas fireplace flame colour is yellow or red flames and is the exception to the rule. Gas fireplace flame colour is typically designed to burn with red flames, not blue flame, for a more natural look.

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

This means that the gas fireplace flame colour breaks 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 red flames.

Propane Fireplace Flame Colour

Propane fireplace flame colour is typically yellow, as propane fireplace flame colour is designed to burn with a more natural look.

As wood logs do not burn with a blue flame colour, neither should a simulated wood fire. A propane fireplace needs yellow or red flames for a realistic look and feel. It is also engineered to operate safely with yellow or red flames, with a flue to eliminate indoor emissions.

Gas Cooker Yellow Flame - Gas Stove Temperature

A gas cooker yellow flame indicates a combustion problem. A gas cooker or stove should have a blue flame.

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 flame. See the flame colour temperature chart above.

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.  

Complete Combustion of LPG Formula:

LPG Gas + Oxygen = Water + Carbon Dioxide + Heat with Blue Flame

 

Air to Gas Ratio for Natural Gas & LPG Proper Combustion

There is a difference is in the air to gas ratio for natural gas & LPG (propane or butane) required for proper combustion. The air to gas ratio for natural gas is around 10:1.

The air to gas ratio for LPG gases is higher. The air to gas ratio for propane gas is approximately 24:1.  The air to gas ratio for butane gas is approximately 31:1.

To achieve this difference, LPG is typically provided in a smaller quantity but at a higher pressure, drawing more oxygen with it into the combustion process, giving LPG a higher air to gas ratio than for natural gas.

Gas Cooker Yellow Flame - Are Yellow or Red Flames on a Gas Cooker Dangerous?

A yellow or red flame on a gas appliance is dangerous, as it is indicative of incomplete combustion and carbon monoxide (CO) generation. A gas cooker yellow flame is a dangerous safety problem, if it occurs with an indoor appliance like a gas stove. You could also be wasting gas.

A gas cooker yellow flame means you should schedule a gas stove service as soon as possible.

 

 

Why Does a Blue Flame Mean it is Safer than Red Flames?

A blue flame means complete combustion is taking place. A key warning sign that your gas appliance requires maintenance are yellow or red flames 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 or red flame.

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 Flames in a Gas Oven

Flames in a gas oven should burn with a blue flame colour, meaning complete combustion, as with other gas appliances. 

Why is a Blue Flame for LPG (Propane) and Yellow-Red Flames on Burning Wood?

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

Burning wood has yellow-red flames 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, yellow or red 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

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 Flame Colour Mean You Save Money?

A blue 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 gas has a blue flame and why it’s a problem if it has yellow or red flames. 

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.