What is a sign of an inefficient oil nozzle?

Increased smoke production during heating is a sign of an inefficient oil nozzle. When the nozzle is not functioning properly, it can lead to incomplete combustion of the heating oil. This inefficiency typically results in the formation of smoke, which is an indication that the oil is not being burned as cleanly as it should be.

In an efficiently operating system, the oil nozzle atomizes the fuel properly, allowing for optimal mixing with air and complete combustion. When the process is compromised, either due to clogging or wear, it leads to scenarios where carbon particles are generated, contributing to visible smoke.

The other options do not directly correlate with inefficiency in the same manner. A consistent flow rate indicates the nozzle is delivering fuel reliably, cold oil flow may be symptomatic of temperature issues rather than nozzle efficiency, and high suction vacuum can relate to other system characteristics but does not explicitly signal inefficiency in the nozzle itself.