Last time I was in England an associate was telling me about how there are mandatory chimney smoke tests done in the UK in order to commission a wood burning unit. If I understand correctly, basically the top of the chimney is sealed off. Then an ignited smoke pellet is dropped in the firebox. Then the base is immediately closed off with plastic in order to trap in the smoke. The tester then has to view the visible areas of the chimney structure to see if any of the smoke comes out around the mortar joints or any other location. I guess the intent is to create a smoke laden positive pressure inside the flue, so you can see the weak points in the chimney structure. My question is...is this type of testing ever done in the US? I know some sweeps use smoke pellets to test chimney draft. But do they also close the top and bottom of the flue and positive pressure test the flue this way?