With complete combustion, what should the flames look like?

In complete combustion, the ideal flame color is blue with orange tips. This indicates a well-optimized burning process where enough oxygen mixes with the fuel, allowing for efficient combustion. The blue color signifies a hot flame with a uniform combustion, which is generally a sign of a properly functioning burner.

The presence of orange tips can occur due to slight variations in the mixture or the combustion process, but the primary and dominant blue color reflects that the combustion is nearly complete and that the fuel is burning efficiently.

A red flame can indicate incomplete combustion and the presence of carbon particles, while yellow flames typically suggest the production of soot, which occurs when there isn't enough air for complete combustion. Green flames are rare and can indicate the presence of certain chemicals or elements, which do not pertain to standard combustion processes in HVAC systems. Thus, a blue flame with orange tips is the hallmark of complete and efficient combustion.