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Solution 3.4 Installation and Operation Manual
8.4.2 Why the chimney should penetrate the highest heated space
When it is cold outside, the warm air in the house is buoyant so it tends to rise. This tendency of
warm air to rise creates a slight pressure difference in the house. Called ‘stack effect’, it produces a
slightly negative pressure low in the house (relative to outside) and a slightly positive pressure
zone high in the house. If there is no fire burning in a heater connected to a chimney that is shorter
than the warm space inside the house, the slight negative pressure low in the house will compete
against the desired upward flow in the chimney.
There are two reasons why the
chimney in the house at right will cold
backdraft when it is cold outside and
there is no fire burning in the stove.
First, the chimney runs up the outside
of the house, so the air in it is colder
and denser than the warm air in the
house. And second, the chimney is
shorter than the heated space of the
house,
meaning
the
negative
pressure low in the house will pull
outside air down the chimney,
through the stove and into the room.
Even the finest stove will not work
well when connected to this chimney.
