Morso 3440 - Draft Conditions

7
ENG
1.9 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 com-
bustion and smoke spillage prevention. However, in cases where the stove door is opened
too vigorously you could expect that slight smoke spillage may occur. The flue gas tempera-
ture at the rated output is 272˚ C relative to 20˚ C. The flue gas flow is 6.7 gr/sec.
If you have some doubts you can ask you local sweeper to measure the draught of the chim-
ney.
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 sto-
ve 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
conditions 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
applies 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.