Excess air is supplied to the burner to provide a safety factor above the actual air required for combustion. A boiler firing without sufficient air, or fuel rich, is operating in a potentially dangerous condition. However, if there is too much air, heat energy from combustion is used to warm the excess cold air, which reduces boiler efficiency. Reducing excess air is one of the most effective boiler improvement techniques. The lower the exhaust gas, the less heat loss.
Flame temperature is raised, increasing radiant heat transfer in the combustion chamber walls.
The increase of efficiency reduces stack temperatures. Pollution is reduced because less fuel is required. This is an excellent time to also have your boilers tuned-up. A good tune-up, using precision test equipment, can detect and correct excess air losses, unburned fuel losses, sooting, fire side fouling and high stack temperatures. When the tune-up is completed, there should be a good record of the boiler s excess air and efficiency across the entire load range, at all existing firing rates.