Matrix Installation and Operation Manual
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8.4
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 stove, slow kindling of new fires, and smoke roll-out when the door is opened for loading.
There are two guidelines to follow. First, the chimney should be installed up through the heated
space of the house, not out and up an outside wall. Second, the chimney should penetrate the top
of the building at or near the highest heated space.
8.4.1
WHY INSIDE CHIMNEYS ARE PREFERRED
Venting systems that rise straight up from the stove flue collar provide the best performance.
Chimneys that rise inside the warm space of the house tend to provide a small amount of draft
even when there is no fire burning. This means that when you light a fire, the initial smoke goes up
the chimney and strong draft builds quickly as the chimney flue warms up. Although they are
common in North America, chimneys that exit a house wall and run up outside can cause
problems.
Good System Design
Inside chimneys are preferred because even when
no fire is burning, there is normally upward flow in
the system.
Inferior System Design
Outside chimneys are a problem because
when no fire burns they will go into cold
backdraft if the stove is installed low in the
house.
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.
