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Black or white smoke emitted from the boiler chimney indicates inadequate combustion leading to excess fuel consumption. Check boiler parameters and settings

The colour of the smoke from the chimney of a boiler is a good first check on combustion.


Black Smoke

White smoke

Grey Smoke

What it indicates

Low air to fuel ratio, i.e. oxygen deficient combustion

High air to fuel ratio, i.e. oxygen rich system

Optimum air to fuel ratio for combustion

Status of Combustion

Incomplete combustion

Complete combustion but the excess air carries away useful heat energy.

Complete combustion with minimized losses

Leads to

Excess fuel consumption due to high unburnt losses

Excess fuel consumption due to higher stack losses.

Optimized fuel consumption.

To keep fuel bills to a minimum, the boiler must not consume more fuel than it actually should. This requires that combustion is complete and without excess air.