What is required at a low firing rate compared to a high firing rate?

At a low firing rate, it is necessary to have more excess air compared to a high firing rate. This additional excess air is needed to ensure complete combustion of the fuel. At lower firing rates, the flame may not be as vigorous, and without sufficient air, incomplete combustion can occur. This can lead to carbon buildup and increased emissions.

In contrast, at higher firing rates, the combustion process is more vigorous and typically better mixes with the fuel, allowing for more efficient burning with less excess air. The increased turbulence and heat contribute to a more complete combustion reaction. Thus, lower firing rates demand more excess air to enhance the combustion efficiency and maintain stable burner operation.