Open the fireplace damper all the way when starting a fire.Let the fire burn for a few minutes then adjust the damper so that it is partially closed (about half way) to see how it affects the fire.

How does a damper operate?

A chimney damper is a manual mechanism that controls airflow and smoke through the chimney flue. A closed damper acts as a seal that keeps the exterior air out and the interior air in. In contrast, an open one sends carbon-monoxide-rich exhaust through the flue and also assists in starting and controlling a fire.

How much should the fireplace damper be open?

A fireplace damper should always be open all of the way when starting a fire, and usually always open throughout the length of the fire. A flue damper should be opened all of the way when opening a stove door to add further fuel to the fire, to help prevent any smoke from pouring out of the stove and into the room.