Distributing the air effectively could also be a challenge. There are easier ways to tame the fireplace. When you place the fire behind the main flow restriction, say a glass door assembly, you can get away with lower flow rates and draft levels without smoke spillage. The barrier between the fire and the room formed by the doors makes the fireplace more spillage-resistant by a huge margin. The doors don't make this fire place an efficient heater, just less of a nuisance.
Some people claim that glass doors spoil a fireplace.
In reality, at least a spark screen is needed to prevent damage to rugs, floors and furniture when the characteristic crackle of the fire spits glowing bits from the hearth. True, glass doors do block out most of the sound of the fire, which is just fine for those of us who find the crackle only makes them apprehensive about those glowing bits. Given the choice of looking through a wire mesh screen or clear glass, I'll take the glass. Beyond the open fireplace at 400 cfm average air demand and the fireplace with doors at 100 cfm, there is a third category in this descending order of air demand. Call it a controlled-combustion fireplace.