Hearthstone Quality Home Heating Products, Inc
® Green Mountain Insert 70 (Model 8450)
21
C
HIMNEY
L
OCATION
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 back drafting when there is no fire
in the insert, slow kindling of new fires, and smoke
roll-out when the door is opened for loading.
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.
Figure 19
– Chimney Location
