In the SI system, how is draft for heating boilers typically measured?

Draft for heating boilers in the SI system is typically measured in millimetres of water head. This measurement indicates the pressure difference that can cause air movement into the combustion chamber of the boiler. The concept behind using millimetres of water head is rooted in the understanding of how pressure is exerted by a column of water; specifically, it represents the height of a water column that would exert the equivalent pressure.

In practical terms, this unit conveys how effectively the boiler can draw in air for combustion, which is crucial for ensuring proper flame stability and optimal efficiency. Measuring draft in this way provides a clear and consistent understanding of how well the system is performing and helps identify any issues such as blockages or insufficient airflow.

Other units like litres per minute relate more to flow rate rather than the pressure differential created by draft. Measurement in degrees Celsius pertains to temperature rather than pressure, and Pascal units, while valid for measuring pressure, are less common in this specific context as millimetres of water head is a more practical and familiar unit for those working in boiler operations.