Osburn 1600 Installation and Operation Manual
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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.
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.