Like everything, your pellet stove will work better if it is well serviced and the pellet stove venting is clear.
Step 1 - Clean the Venting
Your pellet stove should have been supplied with a flue brush for cleaning out the flues and pellet stove pipe of your stove. Clean the flues and vacuum out all loose particles. You can purchase a vent cleaning brush on a flexible shaft that can be as much as 10-feet long.
Step 2 - Brush and Vacuum
Use the long handled vent cleaning brush to clean the venting from the outside. Locate the outside vent and drive the vent cleaning brush through the vent after removing the cover. Use a vacuum cleaner to extract the loose dirt.
Step 3 - Longer Venting
If your pellet stove venting is longer than 10 feet, you need to identify and get access to the joints in the venting to do a thorough job. Joints that can be separated will show a caulk line or tape line. You will have to cut the tape and break the caulk to open the joint and use your vent cleaning brush and vacuum to clean the venting. Re-caulk the joint using heat resistant silicone and ensure that the seal is perfect to stop fumes escaping into the house.
If your pellet stove is professionally serviced, vent cleaning is part of that service.