What is the maximum size of the flue for a gas appliance using a masonry chimney?

The maximum size of the flue for a gas appliance using a masonry chimney is less than 7 times the size of the draft hood outlet. This guideline is important for ensuring proper venting of combustion gases and maintaining the efficiency of the gas appliance.

A flue that is excessively large in relation to the draft hood outlet can lead to insufficient draft, which may result in poor combustion and the potential buildup of harmful gases inside the structure. The size of the flue must be balanced to allow for adequate ventilation while preventing excessive losses of heat and allowing for effective draft performance.

In practical terms, keeping the flue less than 7 times the size of the draft hood outlet ensures that the flue size is appropriate for the appliance's output, allowing for optimal operation and safety. This dimension also aligns with industry standards and building codes designed to promote safe and efficient venting in HVAC applications.