What’s in a Flame? How the Characteristics of a Gas Burner’s Flame Can Reveal Hazards.

Let’s talk about the characteristics of a gas burner flame, especially its color, as it can indicate certain safety conditions. The gas burner flame characteristics discussed here apply to gas ranges, furnaces, water heaters, and any other type of gas appliance.

A word of caution before we continue. Only qualified service technicians should adjust or repair gas burners. The awareness information provided here is directed to everyone, while our diagnostic guidance is from an experienced service technician to other techs. If you see yellow or orange flames or smell the sharp odor of aldehydes sometimes present when deadly carbon monoxide (CO) is produced and you don’t have the experience and training to adjust gas burners, call a service technician. Don’t attempt to adjust burners yourself, as you may worsen the problem or cause an unsafe condition where there previously wasn’t one. ?

General Characteristics of a Burner Flame

Each natural gas or propane consumer should know a little about gas burner flames.

For example, most consumers know from personal experience there are generally three colors of gas burner flames. They are blue, yellow, and orange. It’s possible to have a combination of these colors. The “normal” color for the flame depends on the type of gas it is burning. Normal natural gas burner flames should be completely blue. Propane burner flames should be blue with slight yellow tips. In either case, too much yellow indicates incomplete combustion and the potential presence of deadly CO. Orange flames suggest humidity or particulate matter, such as dust, in the gas supply.

Blue Flames

Properly adjusted blue gas burner flames should be sharp and well-defined, like the flame on a welder’s cutting torch. The flames should be quiet, without an abnormal roaring or blowing sound. Additionally, the size of the flames shouldn’t be too large or too small. This is critical, as even a sharp blue flame can indicate issues in the system or present a hazard if it’s not the correct size.

Service technicians will know the approximate size of properly adjusted gas flames. However, most people can recognize when a burner flame is far too small or too large. Generally, you will know that the flame is too small if it’s difficult to produce enough heat for cooking when the burner is turned to the highest setting.

There are many reasons that a burner could produce small flames, but one common cause is that the appliance is configured for propane while being supplied from a natural gas system. Many gas ranges can be configured for either type of gas. A service technician should be suspicious of the range’s configuration if it was recently installed or is in a mobile home, as mobile homes are sometimes moved and must be reconfigured to use different fuel gases.

You will know that a gas burner’s flames are too large when they impinge upon or touch the burner grate or the bottom of cooking pans. Even if the gas-to-air mixture is correct, impinging flames will cool on the grate's surface or pan before fully burning the fuel. This can cause “incomplete combustion,” which may produce CO as a byproduct. ?

When service technicians arrive after cooking has been completed, it can be challenging to determine the source of CO. However, by checking to see if the gas burner flames are too large, they can determine if that is a possible source of the CO. Impingement is also a factor in water heaters and furnace gas burners.

It's important to note that blue flames can produce CO if, as discussed, the flames impinge on any other surface or the gas system pressure is too high or too low. Service technicians should check for CO on any call where it is suspected. Members of the public should immediately call their gas supplier or a service technician if they have similar suspicions.

Yellow Flames

Yellow flames are usually lazy and drifting, unlike the sharp, well-defined blue flames associated with properly adjusted gas burners. Yellow flames almost always indicate incomplete combustion, meaning the burner has the incorrect gas mixture to air and is less efficient than blue flames. Yellow gas burner flames can also produce unsafe CO and a pungent odor.

But the lack of unpleasant odor doesn’t mean yellow flames are burning safely. CO is odorless and colorless. CO should always be suspected when gas burner flames are any color other than blue. Service technicians should check for CO on any call where yellow flames are observed. Members of the public should immediately call their gas supplier or a service technician in similar situations.

When observing range-top burners, service technicians should check to see if they all exhibit the same characteristics. If there are differences in the appearance of the burners, maladjusted or dirty burners could be the cause. Just as a mechanic can adjust an engine’s carburetor to change the gas-to-air mixture, service technicians can adjust a gas burner when necessary. A properly adjusted carburetor ensures fuel is completely consumed, resulting in maximum power output and low exhaust fumes. Similarly, a service technician can increase or decrease the amount of fuel and air in the burner until the optimum mixture is delivered for combustion.

If all burners have the same yellow appearance, an appliance regulator or gas supply issue may be the cause.

Orange Flames

Orange flames have two leading causes: excess humidity and particulate matter, such as dirt, in the gas stream.

If a service technician responds to a report of orange flames during winter, see if the customer uses a humidifier. As homeowners attempt to keep humidity in their houses to prevent static electricity and to keep the home comfortable, they may use a standalone humidifier or one installed as a component of the home's heating system. One way to determine if humidity is causing the orange flames is to open the doors and windows for several minutes while observing the flames. As the humidity level inside the building is reduced, the flames should become less orange and more blue.

Service technicians have sometimes observed orange gas burner flames after installing a new gas meter or service piping. The particulate matter typically burns off quickly, and the flames become blue.

If burners are improperly adjusted, the abnormal flame characteristics may be limited to only some of the burners. When orange flames are caused by humidity or particulate matter, all range top burners will generally be affected. This observation is an easy test service technicians can use to understand the potential causes of the yellow or orange flames.

Occasionally, it can be difficult to tell whether a flame is yellow or orange since the conditions that cause yellow flames and those that cause orange flames are both present. When yellow or orange flames or some combination of the two are present, service technicians should check for CO. In similar situations, members of the public should immediately call their gas supplier or a qualified service technician.

Keeping Your Family Safe

The next time you prepare to cook on a gas range, take a few seconds to observe the gas burner flames before you set a pan on the grate. The burner works fine if you are supplied with natural gas, and the flames are a pleasant blue color with sharp definition and no unusual noises or odors. If you use propane, these same criteria apply, except you should expect to see small yellow tips on the flames. Service technicians should not attempt to adjust the yellow from the propane burner flames. If they do so, the gas-to-air mixture will be too lean and may potentially produce CO.

CO travels silently, as it is odorless, colorless, and weighs about the same as ordinary room air. So, just as every home should have appropriately positioned smoke detectors, they should also have CO detectors. It’s possible to buy high-quality combination smoke and CO detectors. These vital life safety detectors are not where you want to buy the cheapest. You get what you pay for, so purchase the best and as many as necessary to monitor your entire home. CO detectors should be located and placed in sufficient numbers according to the manufacturer’s instructions to warn occupants of a CO emergency as early as possible.