Originally Posted By: dwickline
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I inspected an oil furnace and when looking at the duct I noticed that there was stuff that looked like creosote that had run down the sides of the duct. The top of the lower sections (male) were inserted into the bottom of the upper sections (female). At first I thought that they were installed backward but then thought that if they were installed the other way that there was a possibility of exhaust fumes escaping. Now I’m a little confused. Please help!