In boiler operation, which color smoke indicates too much air?

• A. Black smoke
• B. White smoke
• C. Blue smoke
• D. Gray smoke

Answer: (B)

The color of the exhaust smoke reflects the air‑to‑fuel ratio in the burner. When there is too much air, the mixture is lean and the flame runs cooler, causing the water vapor produced during combustion to condense and form a visible white plume. That white smoke is a sign that the air supply is excessive and should be reduced to bring the ratio back toward the proper balance. In contrast, too little air leads to a fuel‑rich flame and black smoke due to soot.