Matrix Insert Installation and Operation Manual
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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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