Gas furnaces are an important part of many homes' heating systems. They produce heat reliably year after year as long as they receive the appropriate maintenance. However, if a furnace goes too long without its annual tune-up, it could become less efficient or even develop a yellow or orange flame. An abnormally coloured or shaped gas flame indicates trouble and should never be ignored.
Gas flames burn yellow or orange because they aren't getting enough oxygen. A normal flame should burn steadily and blue. If the flame is temporarily orange because there's a lot of dust in the air, it doesn't indicate a problem. However, if the colour doesn't clear up within a few minutes, the furnace needs attention. It may have a dirty filter, blocked air vents or another more serious problem that requires professional attention.
An orange flame means the gas in the furnace isn't burning completely, which can cause a number of problems, including soot build-up on the inside of the furnace and poisonous carbon monoxide emissions. Never allow a furnace to continue burning with an orange or yellow flame for any significant length of time. It could pose a serious health hazard.
Homeowners can perform some furnace maintenance tasks themselves. Observe the furnace ignition, and ensure that all burners have a steady, blue flame. If the ignition process includes a puff and a small flash, the crossover pieces are clogged with rust or dirt and require cleaning. A dirty burner can also cause a flame that burns too high and can contribute to an orange flame. Shut off the electrical disconnect switch, remove the burner and clean it out by hand. Once the burner is reinstalled, it may burn correctly without any additional problems. Change the furnace filter regularly, too because a dirty filter can keep gas flames from getting enough air.
When simple maintenance techniques don't clear up an orange flame, or if you're uncomfortable dealing with gas appliances, call a service technician. Annual furnace service may seem costly, at between £32 and £97 per session as of January 2011. However, a professional tune-up ensures that your furnace is safe and working efficiently, which can save you significant amounts of money over the course of the year.