The over-fire draft test reading on an oil burner is negative and approximately -0.02 inches of water column.

The over-fire draft test reading on an oil burner is negative and approximately -0.02 inches of water column.

• A. True
• B. False
• C. Cannot be negative
• D. Always positive

Answer: (A)

Over-fire draft is the pressure difference inside the furnace during operation, measured in inches of water column. It should be a small negative value, meaning a gentle suction pulling combustion gases toward the vent rather than pushing them back. A reading around -0.02 inches of water column is typical for an oil burner and indicates normal draft direction and magnitude. The negative sign shows there is suction, not pressure pushing back into the room. If the reading were positive, it would indicate an abnormal condition with the furnace under pressure and potential venting problems. If it were zero or far more negative, adjustments might be needed. So the statement is true because a small negative reading like -0.02 in. wc is a common, acceptable result.

Over-fire draft is the pressure difference inside the furnace during operation, measured in inches of water column. It should be a small negative value, meaning a gentle suction pulling combustion gases toward the vent rather than pushing them back. A reading around -0.02 inches of water column is typical for an oil burner and indicates normal draft direction and magnitude. The negative sign shows there is suction, not pressure pushing back into the room. If the reading were positive, it would indicate an abnormal condition with the furnace under pressure and potential venting problems. If it were zero or far more negative, adjustments might be needed. So the statement is true because a small negative reading like -0.02 in. wc is a common, acceptable result.