Morso 2B Classic - Draft Conditions

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1.8 Draft conditions
If smoke spillage occurs when the fire door is opened, it is probably due to poor chimney draft.
This type of stove requires at least 12 pa of chimney draft to achieve satisfactory combustion
and smoke spillage prevention. However, in cases where the stove door is opened too vigor-
ously you could expect that slight smoke spillage may occur. The smoke gas temperature at
the rated output is 257˚ C relative to 20˚ C.
If you have any doubts, you may want to have your installer measure the draft in the chimney.
Draft conditions
The chimney’s draft is the resulting effect within the flue caused by the difference in
temperature within the flue and the cooler temperature outside. Other factors that
can influence the level of draft include the length of the flue, insulation of the chim-
ney, adverse weather conditions or tall buildings or trees nearby the flue terminal.
Poor draft occurs when:
• Theatmospherictemperaturedifferenceistoolow,e.g.apoorlyinsulatedchim-
ney. If the chimney is excessively cool, it may help to ‘prime’ the flue before the fire
is lit. Just place a screwed-up sheet of newspaper in the flue-ways of the stove and
ignite.
• Theoutsidetemperatureistoohigh,e.g.duringthesummermonths.
• Thereisnoairmovement(wind)outside.
• Thechimneyisnottallenough,withtheresultthattheterminalsitsintheleeof
the roof surface or in the vicinity of tall trees or neighbouring buildings. These con-
ditions are also associated with downdraft where the flue gases are pushed back
down the chimney.
• Fluedraftisdilutedbyresidualairenteringthechimney,e.g.duetoinadequate
flue-pipe joints or leaks at the cleaning door or flue collar.
• Unsealed,unusedreplacesareconnectedtothechimney.
• Theueisblocked,e.g.bysoot,duetoinadequatecleaning,loosedebrisorevena
birds nest.
•Thehouseistootightlysealed(seesectiononFreshairsupply).
A good draft is achieved when:
• Thetemperaturedifferencebetweenthechimneyandoutsideishigh.Thisalsoap-
plies during firing, when the need is greatest.
• Theweatherisclearandthereisagoodwind.
• Thechimneyisoftheproperheight,i.e.minimum4metersoverthestoveandthe
termination adequately clear of the roof line.