There are now fewer open-flue installations in the UK. Graham Elkins highlights why a knowledge of how they operate and what makes them work is essential to ensure the safe removal of products of combustion (POC) to atmosphere.

For an open-flue, the motive force for the flue is produced thermally by the heat of the products of combustion (POC). The motive force relies on the warm POC being replaced by cooler fresh air into the space where the open-flue gas appliance is located. This means that adequate purpose-provided ventilation (where specified) is essential.

Natural draught open-flue systems are typically made up of four parts.
• Primary flue
• Draught diverter (not included on incinerators)
• Secondary flue
• Terminal

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