Can anyone provide some insight into the following question :

State typical requirements for;

i) the percentage of excess air in a natural draught flue?
ii) the percentage of dilution air at the draught diverter in a natural draught flue?

Linkback: https://forum.plumbers.nz/plumbing-gas-fitting-and-drainlaying-apprentice-support/3/natural-draught-flue/412/