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downwind causes a decrease in the depression in the chimney, sometimes causing positive
pressure effects, which means that it nullifies the capacity and extraction of the chimneys.
A predominantly lateral wind has an effect that will depend on the way the chimney is
mounted. To understand this effect, we can indicate that a downwind at 45 with a speed
of 8 m/s (which on a beaufort scale of winds from 0 (ploughing) to 12 (hurricane),
corresponds to a wind of 5 (cool breeze)) causes an effect of increasing the pressure by
about 17 Pa, which can nullify the effect of a chimney that has for example a normal
depression of 12 Pa.
In addition to the direction and strength of the wind and the morphology of the surrounding
terrain, the location and way of placing the chimney in front of the dwelling is also a factor
to be considered.
Figure 17
The depression differences caused by the outside wind are also felt inside the house
and the placement of stoves in the area directly exposed to the wind can increase the
depression created in the chimney, a fact that competes with the pressure caused by the
wind outside the house, which works in an inversely proportional way, that is, the zone of
lower depression will be the area directly exposed to the wind.
In most cases this is not a problem and the depression created by the height of the
chimney nullifies this effect, but whenever this case occurs, it can be compensated by
placing the chimney in the least exposed area, thus increasing the depression capacity of
the chimney.
