We burned approx 4 cords this year (first year buring 24/7) so i figured I would have a sweep out earlier just to be on the safe side. Sweep swept the pipe from the inside in late Feb, said there was some buildup but looked good. Said if i continue to burn dry wood once a year sweep should be adequate. Haven't burned much since he's been out approx 1/2 cord but all of sudden i'm having real issues with drafting and can't get logs to burn. Wood is seasoned but smoke billows into the house when i open the doors. I noticed my chimmney cap is black/brown and seems to have white flakes on it (viewed from the ground). Is it possible that the cap is built up with gunk and restricting airflow? If that is the case what can i clean it with? In the future what should i require of the sweep? Just a cleaning with a brush up the pipe or should they also go up and clean the cap and inspect from the top?