Regarding sootblowing on the air inlet side, remember that what you clean from the heater must pass though the hot end element too, and any large buildup may get caught in the tighter openings of the hot end. If the beposits fly though OK< remeber also that the scanners on the burners may not...
For a large air heater, (size 20 or larger, normally about 3/4" root gap clearance. remember that the heater is probably not round and the gap should be taken after you find the high point on the pin rack.
Also remember that the rotor deflects with the heat, don't run the gear too close to the...