أنشئ حسابًا أو سجّل الدخول للانضمام إلى مجتمعك المهني.
No problem to use concetric reducer or Eccentric reducer
we have to agree that there is acceptable practice and there is a better practice
we may use the concentric reducer this is the acceptable practice.
the better one is using eccentric reducer, if you search ASHRAE standards you will not find any restriction.