Gas Heat ESCO Practice Exam 2026 - Free Gas Heat ESCO Practice Questions and Study Guide

Good combustion in a gas furnace is indicated by a blue flame coloration in the burner. This blue coloration signifies that the gas is burning efficiently and completely, which is essential for optimal performance and safety. A blue flame means that the combustion is occurring with enough oxygen, producing a clean burn with minimal harmful emissions, such as carbon monoxide, and maximizing the heat output from the gas being consumed.

In contrast, other flame colors can suggest incomplete combustion or inefficient burning. For example, a flickering yellow flame may indicate that the gas is not burning completely, often due to a lack of oxygen, which can lead to soot buildup and potentially hazardous conditions. A steady green flame can suggest the presence of contaminants in the gas or burner, while a bright orange flame typically indicates inefficient combustion and can also signify a problem, such as dust in the burner or insufficient air supply, leading to lower efficiency and increased emissions. Therefore, the presence of a blue flame is the hallmark of proper combustion in a gas furnace system.