I agree with Skidder's thoughts. I am note sure what size intake you are thinking of, but remember on a UDS style smoker/cooker that the fire is controlled by the air intake. Bringing the air in from the sides has worked very well throughout this thread. The bottom of the charcoal basket being 2 1/2 to 3" off the floor takes care of ashing when the air comes in from the sides.
Charbroil Vertical Propane Smoker, Weber Silver Gasser, UDS, Maverick 732. Weber 18.5" Silver, Weber Redhead Stainless Performer, Blue Weber 22.5 Gold, 18.5" WSM