What could a yellow flame in a gas furnace indicate?

A yellow flame in a gas furnace is an important indicator of combustion quality. It signifies incomplete combustion, which occurs when there is not enough oxygen to burn the gas completely. This can lead to the production of carbon monoxide, a dangerous byproduct, and is often caused by dirty burners or blocked air supply. The ideal flame color indicating complete combustion is blue, which shows the gas is burning efficiently with proper air-to-fuel ratio.

The presence of a yellow flame also suggests that the furnace is not operating at peak efficiency, potentially leading to higher energy costs and reduced performance. Therefore, the yellow flame serves as a warning sign that maintenance may be needed to ensure safety and optimal function of the heating system.