velvetfoot said:I have to read more about downdraft, but that's a good point about using smoke to track air leaving the house.
IR would be useless there.
I like the fizzing beer analogy too.
Thanks.
Pay specific attention to the concept of “stack effect” (chapter 10), as that is what causes a backflowing flue.
thechimneysweep said:Pay specific attention to the concept of “stack effect” (chapter 10), as that is what causes a backflowing flue.
The stack effect is only one possible cause of a backflowing flue, and is far from the most common. We generally only see the stack effect in older multi-story houses, where heated air rises and exits out the (leaky) upper story, vacuuming replacement air down the chimney.
In our area, largely populated by newer, one-story homes without leaky attic doors, it is very rare to see smoke backflow caused by the stack effect. The most prevalent causes of chimney backflow are mechanical depressurization, wind-induced downdrafting, flue blockage and atmospheric air inversion. There are many other common causes, some of which can be viewed at (broken link removed to http://www.chimneysweeponline.com/hodraft.htm).
However, I must agree with the other posters that failure to prime a cold flue will result in smoke spillage nearly every time. Until the cold-air "plug" has been displaced, the chimney wants to flow backward, carrying the smoke back into the house.
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