A company by the name of Kathabar carries a product line for total energy recovery with no cross contamination of the supply/exhaust air streams; I believe its called twin-cel...
Start at 1 then 2 (at 180deg from 1) then 3 90 deg from 2 then 4 (180 deg from 3)and so on. Scale up the procedure from the following link till you reach your max torque.
http://www.piping-designer.com/Bolt_Tightening_Procedure