The flue or chimney must extend how high above the roof?

The requirement for a flue or chimney to extend above the roof is primarily dictated by safety and efficiency concerns. In general, the height of the chimney should be at least 2 feet above the highest point of the roof that is within 10 horizontal feet. This height ensures that the combustion gases are effectively vented away from the roof and do not pose a hazard, such as backdrafts or the risk of ignition of combustible materials on or near the roof.

By extending the flue or chimney 2 feet higher than the roof, it creates a sufficient draft to promote the proper exhaust of flue gases. It also minimizes the risk of downdrafts, which can occur in windy conditions, allowing smoke and other emissions to escape freely without re-entering the living spaces. This regulation is essential for maintaining indoor air quality and ensuring the safe operation of heating systems.

Other choices do not meet the minimum requirement set forth by building codes and standards, which is designed to ensure both safety and effective ventilation.