©
EUROHEAT
DISTRIBUTORS (H.B.S) LTD. March 2006
Technical Guide IN1087 Edition C
28
Spring and Autumn Syndrome
A additional guide to show the influences of seasonal temperatures upon the
operation of a stove and flue system.
Stoves utilize the effect of air current within the flue to both exhaust
the products of combustion and to induce air into the stove. Normally,
because the air within the house is warmer than the outside air the flue
is exhausting air from the stove even when it is not operating.
1. A hot flue does not “draw” air into a stove, it is the differences of
densities that motivate the lighter gases upwards.
2. The greater the temperature difference between the gases within the
flue and the surrounding air, the greater the difference in densities and
the greater the motivation.
3. The taller the flue, the greater the weight of the equivalent volume
of denser air, the greater the motivation.
During the very changeable whether conditions of Spring and
Autumn the outside temperature can rise suddenly and become
warmer than the temperature within the house. This causes the
air within the flue to reverse its normal flow pattern and air travels
down the flue. The most obvious outcome of this will initially
be a smell from the flue and whilst this is not harmful it may be
unpleasant if the flue has not been swept as often as it should
have been.
Because of the warmer outside temperature the house will feel
colder than it actually is, and the desire to light the stove and at
least match the outside temperature will reveal another problem,
the stove will not light. If sufficient air is coming down the flue the
stove will appear to begin its lighting cycle but smoke will emanate
from what are normally air inlets and into the room. The stove
may continue to operate in this fashion for a considerable time but
because the flue is operating in reverse there is no possibility of
any hot air produced by the stove travelling up the flue, to warm
it, and reverse the flow.
