Minimum Chimney Height; The Relationship Between The Chimney And The House; Why The Chimney Should Penetrate The Highest Heated Space - Osburn 2000 Installation And Operation Manual

2000 Insert Installation and Operation Manual
9.6 MINIMUM CHIMNEY
HEIGHT
The top of the chimney should be tall
enough to be above the air
turbulence caused when wind blows
against the house and its roof. The
chimney must extend at least 1 m (3
ft.) above the highest point of
contact with the roof, and at least 60
cm (2 ft.) higher than any roof line or
obstacle within a horizontal distance
of 3 m (10 ft.).
9.7 THE RELATIONSHIP BETWEEN THE CHIMNEY AND THE HOUSE
Because the venting system is the engine that drives the wood heating system, it must have the
right characteristics. The signs of bad system design are cold backdrafting when there is no fire in
the insert, slow kindling of new fires, and smoke roll‐out when the door is opened for loading.
9.7.1 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 insert. 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 insert and into the room. Even the
finest insert will not work well when
connected to this chimney.
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