A natural gas flame should be blue, which indicates proper combustion. Long streaks of yellow or orange through the flame means the furnace needs adjustment and/or cleaning by a professional service technician. It could also mean you have a cracked heat exchanger. The burners shown below are an example of a furnace that needs service. 

    Colors other than blue indicate incomplete combustion of the gas due to insufficient air for combustion. This also increases the amount of carbon monoxide (CO) produced. We recommend you take a peek at the gas burners, while the system is operating, at the beginning of your heating season each year. If you don’t like the color of the flame, or the flame pattern is irregular or wavering, like in the photo below, call a service tech for further evaluation. An even better idea is to have a service contract with a heating and air conditioning company that checks your complete system annually.

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.