Lack of draught
: A chimney is like a hot air balloon, the air inside want to rise up as it is
hotter that the air outside. The 2 things that determine the performance of a hot air balloon
are the size of the balloon, which equates to the height and diameter of your flue, and the
temperature of the air inside, which equates to the quality of the chimney. If the pilot wants
to go up, he turns the burner on and heats the air so it has more lift. If you have a large ‘cold’
chimney, as the smoke goes up it will cool and lose its buoyancy. This stops the rise and it is
this rise or draw, that removes the products of combustion. The pellet burner has a fan built
in to on initial lighting for about 2 minutes the cooker can be under positive pressure and a
small amount of smoke can be forced back into the ovens if they are left open at this stage.
This is safe and clears as soon as the chimney warms a few degrees above ambient and then
has a negative pressure or draw.
Signs of lack of draw
: When, at all times, quantities of smoke come out joints and from the
oven vents when the oven door is open.
Solutions:
Check that the flue is not blocked in the first place. Line the chimney, insulate the
chimney/liner. No cowls will increase draw, they all reduce it.
Down Draught
: A roof is like the wing of an aircraft or the sail on a boat and causes pressure
changes as the wind flows over and around it. To make matters worse, the surroundings also
affect the flow and pressures. So if a chimney it not ‘tall’ enough it can end up in a high
pressure zone, the air will then want to come down the chimney and out the back or front
door, which can be at a lower pressure.
Signs of a down draft:
When quantities of smoke come out joints and from the oven vents
when the oven door is open, on certain days only when the wind is blowing from a particular
direction. (Usually from the opposite side of the roof that the chimney is
Solutions:
Raise the chimney, more twin wall or taller pot. Cut down surrounding trees. Fit a
‘Verdette’ or spinning type of cowl.
Summary of Contents for Range cooker
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