There are a number of ways you can improve the performance of your woodburner.
Clean the Chimney - The best way to improve draw is by cleaning the flue system. You should have your chimney cleaned yearly, before the winter season. If you are burning wet wood, the fire will have to dry the wood before it is burnt, which also causes build up of cresote inside the flue. Using a mixture of hard and dry wood will give the most heat from the fire.
Check the flue length and design - A flue which is too short will not allow enough draught for the fire, and a flue with too many bends can also restrict airflow. Without enough clearance, your chimney will not have adequate draught. Check with your Warmington dealer to make sure you purchase the right flue for your fire.