NESTOR MARTIN H11 Mode D'emploi page 49

If the flue terminal is too low in relation to the roof, or is masked by other buildings, it is possible for winds
coming from certain directions to have become so turbulent that the stove's stabilizer will be unable to respond
quickly enough to the changing conditions. Trees often create turbulence problems that cause difficulties
because they are often overlooked in the search for the culprit. Not only are the aero-dynamics of trees changed
with the seasons and leaf growth, but a large tree may have no effect for many years and its last foot of growth
may never be suspected as the cause of a previously well controlled stove becoming erratic. No « patented »
cowl fitted to the flue terminal will overcome serious wind turbulence, but minor turbulence can often be
reduced to acceptable levels with a suitable «model» . For major turbulence problems, increasing the height of
your existing flue or demolishing the offending obstruction will be the only effective cure.
The term «down draught» is often used erroneously to explain almost any flue unable to sustain sufficient
thermally induced gas speed to overcome high pressure zones caused by winds hitting an obstruction beyond the
flue terminal. In most instances this is caused by a poor flue cooling the flue gasses and a cure would be effected
with an insulated pipe. True « down draught » affects houses situated on or near to hills, when cooling air travels
down the hillside.
This wind, called katabatic wind, can normally be controlled with an efficient flue system and suitable cowl, but if
the wind causes a high pressure zone at the flue terminal, resitting the flue to the opposite side of the house may
be the only effective answer if an otherwise satisfactory flue causes a problem. The opposite condition, when
warming air travels up a hillside giving anabatic wind, can produce very high negative flue pressures which will
sometimes necessitate a barometric damper being fitted to the flue.
Windows and doors opened down wind of prevailing winds and the running of large extraction fans without
adequate ventilation may cause the flue to stall or even become positively pressurised with potentially dangerous
consequences. Any smell of flue gasses within the house should be investigated immediately. Damp weather is
one of a multitude of atmospheric conditions blamed for poor flue « draught » . There is no theoretical or
practical foundation for these, only the existence of an oversized, cold and damp chimney needing lining and
insulating.
VENTILATION
The ventilation to provide the stove with air has to be regarded as an integral part of the flue system, because
unless the air passing through the flue is replaced with equal amounts of air entering the house, the flue will
cease to function. The colder the outside temperature and the harder the stove is working to maintain the
required temperature inside, the colder the incoming air and the greater its flow. No amount of strategically
positioned knitted draught excluders will overcome the laws of physics or your discomfort if ventilation not being
given the planning it deserves.
Any room or space containing an appliance should have a permanent ventilation opening of free area at least 550
2
mm (0.8525 square inches) for every kilowatt (3,412 BTU) of rated output above 5 kilowatts (17,060 BTU)
C07100DC023
48