DEP Boiler Chimney Size Methodology/Calculation

All,



I have a situation where our chimney flue has been sized and installed per ASHRAE standards.



However, we can't get sign-off since the PE signing the drawings says our chimney is too small and there's insufficient draft. He says he's using the DEP methodology for chimney sizing. I can't find this anywhere. Can anyone point me in the right direction?



This is in NYC and the boilers/chimney have been working like a charm...