Chimney draft blockage causes
A blockage of the chimney draft is a common chimney problem. This happens because of poor maintenance or maybe even structural issues. Some of the main chimney blockage causes are:
Wrong chimney height
Sometimes, due to the insufficient height of the chimney, the so called, ambient updraft effect take place.
Sometimes, the dimensions of the chimney have nothing to do with the fact that the draft is blocked. In many cases, the problem may be with the flue, which can be blocked by debris that fall into the chimney. Things like nests, tree branches, fallen bricks, etc., all of them can block the flue and thus, block the draft.
Make sure the chimney is clean and it has enough combustion air. Because a chimney pulls air through the fireplace, negative air pressure can occur and eliminate the draft, even causing smoke to be eliminated through the fireplace instead of the chimney top.
If the chimney flue is connected to some other house appliance in the house, the air may leak through that appliance. This is also available for cracks in connector pipes, thimble fitting, etc. Too much updraft can also lead to problems. It is best you find a middle way solution. Make sure the fireplace isn’t burning excessively and air-leak the door and glass gaskets.