We have had white/blue smoke puffs coming out of the oil burner duct, whenever the heat initially clicks on, for several years now. We have had the burner serviced annually and by 3 different techs from 3 different companies. They replace nozzle and filter, clean it out and tell me it's fine, but it still concerns me. The last tech said it may be partly due to the fact that the duct work from furnace to where it leaves the house is about 10 feet long, that some oil may settle in there and when it turns on it is just cleaning it out. Does that make sense to you guys?